draft-ietf-cellar-flac-00.txt   draft-ietf-cellar-flac-01.txt 
cellar J. Coalson cellar M. Sandelman
Internet-Draft Internet-Draft
Intended status: Standards Track Intended status: Informational A. Weaver
Expires: January 30, 2020 Xiph.Org Foundation Expires: 29 October 2021 27 April 2021
A. Weaver
July 29, 2019
Free Lossless Audio Codec Free Lossless Audio Codec
draft-ietf-cellar-flac-00 draft-ietf-cellar-flac-01
Abstract Abstract
This document defines FLAC, which stands for Free Lossless Audio This document defines FLAC, which stands for Free Lossless Audio
Codec, a free, open source codec for lossless audio compression and Codec, a free, open source codec for lossless audio compression and
decompression. decompression.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
skipping to change at page 1, line 34 skipping to change at page 1, line 32
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This Internet-Draft will expire on January 30, 2020. This Internet-Draft will expire on 29 October 2021.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notation and Conventions . . . . . . . . . . . . . . . . . . 3 2. Notation and Conventions . . . . . . . . . . . . . . . . . . 3
3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 3 3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 3
4. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8. Interchannel Decorrelation . . . . . . . . . . . . . . . . . 6 8. Interchannel Decorrelation . . . . . . . . . . . . . . . . . 6
9. Prediction . . . . . . . . . . . . . . . . . . . . . . . . . 6 9. Prediction . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Residual Coding . . . . . . . . . . . . . . . . . . . . . . . 7 10. Residual Coding . . . . . . . . . . . . . . . . . . . . . . . 8
11. Format . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 11. Format . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Conventions . . . . . . . . . . . . . . . . . . . . . . 11 11.1. Conventions . . . . . . . . . . . . . . . . . . . . . . 12
11.2. STREAM . . . . . . . . . . . . . . . . . . . . . . . . . 12 11.2. STREAM . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.3. METADATA_BLOCK . . . . . . . . . . . . . . . . . . . . . 12 11.3. METADATA_BLOCK . . . . . . . . . . . . . . . . . . . . . 13
11.4. METADATA_BLOCK_HEADER . . . . . . . . . . . . . . . . . 12 11.4. METADATA_BLOCK_HEADER . . . . . . . . . . . . . . . . . 13
11.5. BLOCK_TYPE . . . . . . . . . . . . . . . . . . . . . . . 12 11.5. BLOCK_TYPE . . . . . . . . . . . . . . . . . . . . . . . 14
11.6. METADATA_BLOCK_DATA . . . . . . . . . . . . . . . . . . 13 11.6. METADATA_BLOCK_DATA . . . . . . . . . . . . . . . . . . 14
11.7. METADATA_BLOCK_STREAMINFO . . . . . . . . . . . . . . . 13 11.7. METADATA_BLOCK_STREAMINFO . . . . . . . . . . . . . . . 15
11.8. METADATA_BLOCK_PADDING . . . . . . . . . . . . . . . . . 14 11.8. METADATA_BLOCK_PADDING . . . . . . . . . . . . . . . . . 16
11.9. METADATA_BLOCK_APPLICATION . . . . . . . . . . . . . . . 15 11.9. METADATA_BLOCK_APPLICATION . . . . . . . . . . . . . . . 16
11.10. METADATA_BLOCK_SEEKTABLE . . . . . . . . . . . . . . . . 15 11.10. METADATA_BLOCK_SEEKTABLE . . . . . . . . . . . . . . . . 16
11.11. SEEKPOINT . . . . . . . . . . . . . . . . . . . . . . . 15 11.11. SEEKPOINT . . . . . . . . . . . . . . . . . . . . . . . 17
11.12. METADATA_BLOCK_VORBIS_COMMENT . . . . . . . . . . . . . 16 11.12. METADATA_BLOCK_VORBIS_COMMENT . . . . . . . . . . . . . 17
11.13. METADATA_BLOCK_CUESHEET . . . . . . . . . . . . . . . . 16 11.13. METADATA_BLOCK_CUESHEET . . . . . . . . . . . . . . . . 18
11.14. CUESHEET_TRACK . . . . . . . . . . . . . . . . . . . . . 18 11.14. CUESHEET_TRACK . . . . . . . . . . . . . . . . . . . . . 19
11.15. CUESHEET_TRACK_INDEX . . . . . . . . . . . . . . . . . . 19 11.15. CUESHEET_TRACK_INDEX . . . . . . . . . . . . . . . . . . 20
11.16. METADATA_BLOCK_PICTURE . . . . . . . . . . . . . . . . . 19 11.16. METADATA_BLOCK_PICTURE . . . . . . . . . . . . . . . . . 20
11.17. PICTURE_TYPE . . . . . . . . . . . . . . . . . . . . . . 19 11.17. PICTURE_TYPE . . . . . . . . . . . . . . . . . . . . . . 21
11.18. FRAME . . . . . . . . . . . . . . . . . . . . . . . . . 20 11.18. FRAME . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.19. FRAME_HEADER . . . . . . . . . . . . . . . . . . . . . . 20 11.19. FRAME_HEADER . . . . . . . . . . . . . . . . . . . . . . 23
11.19.1. FRAME HEADER RESERVED . . . . . . . . . . . . . . . 21 11.19.1. FRAME HEADER RESERVED . . . . . . . . . . . . . . . 23
11.19.2. BLOCKING STRATEGY . . . . . . . . . . . . . . . . . 21 11.19.2. BLOCKING STRATEGY . . . . . . . . . . . . . . . . . 24
11.19.3. INTERCHANNEL SAMPLE BLOCK SIZE . . . . . . . . . . 22 11.19.3. INTERCHANNEL SAMPLE BLOCK SIZE . . . . . . . . . . 24
11.19.4. SAMPLE RATE . . . . . . . . . . . . . . . . . . . . 22 11.19.4. SAMPLE RATE . . . . . . . . . . . . . . . . . . . . 25
11.19.5. CHANNEL ASSIGNMENT . . . . . . . . . . . . . . . . 23 11.19.5. CHANNEL ASSIGNMENT . . . . . . . . . . . . . . . . 26
11.19.6. SAMPLE SIZE . . . . . . . . . . . . . . . . . . . . 23 11.19.6. SAMPLE SIZE . . . . . . . . . . . . . . . . . . . . 27
11.19.7. FRAME HEADER RESERVED2 . . . . . . . . . . . . . . 24 11.19.7. FRAME HEADER RESERVED2 . . . . . . . . . . . . . . 27
11.19.8. CODED NUMBER . . . . . . . . . . . . . . . . . . . 24 11.19.8. CODED NUMBER . . . . . . . . . . . . . . . . . . . 27
11.19.9. BLOCK SIZE INT . . . . . . . . . . . . . . . . . . 24 11.19.9. BLOCK SIZE INT . . . . . . . . . . . . . . . . . . 28
11.19.10. SAMPLE RATE INT . . . . . . . . . . . . . . . . . . 24 11.19.10. SAMPLE RATE INT . . . . . . . . . . . . . . . . . . 28
11.19.11. FRAME CRC . . . . . . . . . . . . . . . . . . . . . 25 11.19.11. FRAME CRC . . . . . . . . . . . . . . . . . . . . . 28
11.20. FRAME_FOOTER . . . . . . . . . . . . . . . . . . . . . . 25 11.20. FRAME_FOOTER . . . . . . . . . . . . . . . . . . . . . . 28
11.21. SUBFRAME . . . . . . . . . . . . . . . . . . . . . . . . 25 11.21. SUBFRAME . . . . . . . . . . . . . . . . . . . . . . . . 29
11.22. SUBFRAME_HEADER . . . . . . . . . . . . . . . . . . . . 25 11.22. SUBFRAME_HEADER . . . . . . . . . . . . . . . . . . . . 29
11.22.1. SUBFRAME TYPE . . . . . . . . . . . . . . . . . . . 25 11.22.1. SUBFRAME TYPE . . . . . . . . . . . . . . . . . . . 29
11.22.2. WASTED BITS PER SAMPLE FLAG . . . . . . . . . . . . 26 11.22.2. WASTED BITS PER SAMPLE FLAG . . . . . . . . . . . . 30
11.23. SUBFRAME_CONSTANT . . . . . . . . . . . . . . . . . . . 26 11.23. SUBFRAME_CONSTANT . . . . . . . . . . . . . . . . . . . 30
11.24. SUBFRAME_FIXED . . . . . . . . . . . . . . . . . . . . . 26 11.24. SUBFRAME_FIXED . . . . . . . . . . . . . . . . . . . . . 30
11.25. SUBFRAME_LPC . . . . . . . . . . . . . . . . . . . . . . 27 11.25. SUBFRAME_LPC . . . . . . . . . . . . . . . . . . . . . . 31
11.26. SUBFRAME_VERBATIM . . . . . . . . . . . . . . . . . . . 27 11.26. SUBFRAME_VERBATIM . . . . . . . . . . . . . . . . . . . 31
11.27. RESIDUAL . . . . . . . . . . . . . . . . . . . . . . . . 27 11.27. RESIDUAL . . . . . . . . . . . . . . . . . . . . . . . . 31
11.27.1. RESIDUAL_CODING_METHOD . . . . . . . . . . . . . . 27 11.27.1. RESIDUAL_CODING_METHOD . . . . . . . . . . . . . . 32
11.27.2. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB . . . 28 11.27.2. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB . . . 32
11.27.3. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2 . . 29 11.27.3. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2 . . 33
11.27.4. ENCODED RESIDUAL . . . . . . . . . . . . . . . . . 29 11.27.4. ENCODED RESIDUAL . . . . . . . . . . . . . . . . . 34
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 12. Normative References . . . . . . . . . . . . . . . . . . . . 34
12.1. Normative References . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
12.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction 1. Introduction
This is a detailed description of the FLAC format. There is also a This is a detailed description of the FLAC format. There is also a
companion document that describes FLAC-to-Ogg mapping [1]. companion document that describes FLAC-to-Ogg mapping
(https://xiph.org/flac/ogg_mapping.html).
For a user-oriented overview, see About the FLAC Format [2]. For a user-oriented overview, see About the FLAC Format
(https://xiph.org/flac/documentation_format_overview.html).
2. Notation and Conventions 2. Notation and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Acknowledgments 3. Acknowledgments
FLAC owes much to the many people who have advanced the audio FLAC owes much to the many people who have advanced the audio
compression field so freely. For instance: - A. J. Robinson [3] compression field so freely. For instance: - A. J. Robinson
for his work on Shorten [4]; his paper is a good starting point on (http://svr-www.eng.cam.ac.uk/~ajr/) for his work on Shorten
some of the basic methods used by FLAC. FLAC trivially extends and (http://svr-www.eng.cam.ac.uk/reports/abstracts/robinson_tr156.html);
improves the fixed predictors, LPC coefficient quantization, and his paper is a good starting point on some of the basic methods used
Exponential-Golomb coding used in Shorten. - S. W. Golomb [5] and by FLAC. FLAC trivially extends and improves the fixed predictors,
Robert F. Rice; their universal codes are used by FLAC's entropy LPC coefficient quantization, and Exponential-Golomb coding used in
coder. - N. Levinson and J. Durbin; the reference encoder uses an Shorten. - S. W. Golomb
algorithm developed and refined by them for determining the LPC (https://web.archive.org/web/20040215005354/http://csi.usc.edu/
coefficients from the autocorrelation coefficients. - And of course, faculty/golomb.html) and Robert F. Rice; their universal codes are
Claude Shannon [6] used by FLAC's entropy coder. - N. Levinson and J. Durbin; the
reference encoder uses an algorithm developed and refined by them for
determining the LPC coefficients from the autocorrelation
coefficients. - And of course, Claude Shannon
(http://en.wikipedia.org/wiki/Claude_Shannon)
4. Scope 4. Scope
It is a known fact that no algorithm can losslessly compress all It is a known fact that no algorithm can losslessly compress all
possible input, so most compressors restrict themselves to a useful possible input, so most compressors restrict themselves to a useful
domain and try to work as well as possible within that domain. domain and try to work as well as possible within that domain.
FLAC's domain is audio data. Though it can losslessly code any FLAC's domain is audio data. Though it can losslessly code any
input, only certain kinds of input will get smaller. FLAC exploits input, only certain kinds of input will get smaller. FLAC exploits
the fact that audio data typically has a high degree of sample-to- the fact that audio data typically has a high degree of sample-to-
sample correlation. sample correlation.
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default parameters of the reference encoder are tuned to CD-quality default parameters of the reference encoder are tuned to CD-quality
music data (i.e. 44.1 kHz, 2 channel, 16 bits per sample). The music data (i.e. 44.1 kHz, 2 channel, 16 bits per sample). The
effect of the encoding parameters on different kinds of audio data effect of the encoding parameters on different kinds of audio data
will be examined later. will be examined later.
5. Architecture 5. Architecture
Similar to many audio coders, a FLAC encoder has the following Similar to many audio coders, a FLAC encoder has the following
stages: stages:
o "Blocking" (see Section 7). The input is broken up into many * "Blocking" (see section on Blocking (#blocking)). The input is
contiguous blocks. With FLAC, the blocks MAY vary in size. The broken up into many contiguous blocks. With FLAC, the blocks MAY
optimal size of the block is usually affected by many factors, vary in size. The optimal size of the block is usually affected
including the sample rate, spectral characteristics over time, by many factors, including the sample rate, spectral
etc. Though FLAC allows the block size to vary within a stream, characteristics over time, etc. Though FLAC allows the block size
the reference encoder uses a fixed block size. to vary within a stream, the reference encoder uses a fixed block
size.
o "Interchannel Decorrelation" (see Section 8). In the case of * "Interchannel Decorrelation" (see section on Interchannel
Decorrelation (#interchannel-decorrelation)). In the case of
stereo streams, the encoder will create mid and side signals based stereo streams, the encoder will create mid and side signals based
on the average and difference (respectively) of the left and right on the average and difference (respectively) of the left and right
channels. The encoder will then pass the best form of the signal channels. The encoder will then pass the best form of the signal
to the next stage. to the next stage.
o "Prediction" (see Section 9). The block is passed through a * "Prediction" (see section on Prediction (#prediction)). The block
prediction stage where the encoder tries to find a mathematical is passed through a prediction stage where the encoder tries to
description (usually an approximate one) of the signal. This find a mathematical description (usually an approximate one) of
description is typically much smaller than the raw signal itself. the signal. This description is typically much smaller than the
Since the methods of prediction are known to both the encoder and raw signal itself. Since the methods of prediction are known to
decoder, only the parameters of the predictor need be included in both the encoder and decoder, only the parameters of the predictor
the compressed stream. FLAC currently uses four different classes need be included in the compressed stream. FLAC currently uses
of predictors, but the format has reserved space for additional four different classes of predictors, but the format has reserved
methods. FLAC allows the class of predictor to change from block space for additional methods. FLAC allows the class of predictor
to block, or even within the channels of a block. to change from block to block, or even within the channels of a
block.
o "Residual Coding" (See Section 10). If the predictor does not * "Residual Coding" (See section on Residual Coding (#residual-
describe the signal exactly, the difference between the original coding)). If the predictor does not describe the signal exactly,
signal and the predicted signal (called the error or residual the difference between the original signal and the predicted
signal) MUST be coded losslessly. If the predictor is effective, signal (called the error or residual signal) MUST be coded
the residual signal will require fewer bits per sample than the losslessly. If the predictor is effective, the residual signal
original signal. FLAC currently uses only one method for encoding will require fewer bits per sample than the original signal. FLAC
the residual, but the format has reserved space for additional currently uses only one method for encoding the residual, but the
methods. FLAC allows the residual coding method to change from format has reserved space for additional methods. FLAC allows the
block to block, or even within the channels of a block. residual coding method to change from block to block, or even
within the channels of a block.
In addition, FLAC specifies a metadata system, which allows arbitrary In addition, FLAC specifies a metadata system, which allows arbitrary
information about the stream to be included at the beginning of the information about the stream to be included at the beginning of the
stream. stream.
6. Definitions 6. Definitions
Many terms like "block" and "frame" are used to mean different things Many terms like "block" and "frame" are used to mean different things
in different encoding schemes. For example, a frame in MP3 in different encoding schemes. For example, a frame in MP3
corresponds to many samples across several channels, whereas an S/ corresponds to many samples across several channels, whereas an S/
PDIF frame represents just one sample for each channel. The PDIF frame represents just one sample for each channel. The
definitions we use for FLAC follow. Note that when we talk about definitions we use for FLAC follow. Note that when we talk about
blocks and subblocks we are referring to the raw unencoded audio data blocks and subblocks we are referring to the raw unencoded audio data
that is the input to the encoder, and when we talk about frames and that is the input to the encoder, and when we talk about frames and
subframes, we are referring to the FLAC-encoded data. subframes, we are referring to the FLAC-encoded data.
o *Block*: One or more audio samples that span several channels. * *Block*: One or more audio samples that span several channels.
o *Subblock*: One or more audio samples within a channel. A block * *Subblock*: One or more audio samples within a channel. A block
contains one subblock for each channel, and all subblocks contain contains one subblock for each channel, and all subblocks contain
the same number of samples. the same number of samples.
o *Blocksize*: The number of samples in any of a block's subblocks. * *Blocksize*: The number of samples in any of a block's subblocks.
For example, a one second block sampled at 44.1 kHz has a For example, a one second block sampled at 44.1 kHz has a
blocksize of 44100, regardless of the number of channels. blocksize of 44100, regardless of the number of channels.
o *Frame*: A frame header plus one or more subframes. * *Frame*: A frame header plus one or more subframes.
o *Subframe*: A subframe header plus one or more encoded samples * *Subframe*: A subframe header plus one or more encoded samples
from a given channel. All subframes within a frame will contain from a given channel. All subframes within a frame will contain
the same number of samples. the same number of samples.
o *Exponential-Golomb coding*: One of Robert Rice's universal coding * *Exponential-Golomb coding*: One of Robert Rice's universal coding
schemes, FLAC's residual coder, compresses data by writing the schemes, FLAC's residual coder, compresses data by writing the
number of bits to be read minus 1, before writing the actual number of bits to be read minus 1, before writing the actual
value. value.
o *LPC*: Linear predictive coding [7]. * *LPC*: Linear predictive coding (https://en.wikipedia.org/wiki/
Linear_predictive_coding).
7. Blocking 7. Blocking
The size used for blocking the audio data has a direct effect on the The size used for blocking the audio data has a direct effect on the
compression ratio. If the block size is too small, the resulting compression ratio. If the block size is too small, the resulting
large number of frames mean that excess bits will be wasted on frame large number of frames mean that excess bits will be wasted on frame
headers. If the block size is too large, the characteristics of the headers. If the block size is too large, the characteristics of the
signal MAY vary so much that the encoder will be unable to find a signal MAY vary so much that the encoder will be unable to find a
good predictor. In order to simplify encoder/decoder design, FLAC good predictor. In order to simplify encoder/decoder design, FLAC
imposes a minimum block size of 16 samples, and a maximum block size imposes a minimum block size of 16 samples, and a maximum block size
skipping to change at page 6, line 27 skipping to change at page 6, line 49
constant subframe, and the other an LPC subframe. constant subframe, and the other an LPC subframe.
8. Interchannel Decorrelation 8. Interchannel Decorrelation
In stereo streams, many times there is an exploitable amount of In stereo streams, many times there is an exploitable amount of
correlation between the left and right channels. FLAC allows the correlation between the left and right channels. FLAC allows the
frames of stereo streams to have different channel assignments, and frames of stereo streams to have different channel assignments, and
an encoder MAY choose to use the best representation on a frame-by- an encoder MAY choose to use the best representation on a frame-by-
frame basis. frame basis.
o *Independent*. The left and right channels are coded * *Independent*. The left and right channels are coded
independently. independently.
o *Mid-side*. The left and right channels are transformed into mid * *Mid-side*. The left and right channels are transformed into mid
and side channels. The mid channel is the midpoint (average) of and side channels. The mid channel is the midpoint (average) of
the left and right signals, and the side is the difference signal the left and right signals, and the side is the difference signal
(left minus right). (left minus right).
o *Left-side*. The left channel and side channel are coded. * *Left-side*. The left channel and side channel are coded.
o *Right-side*. The right channel and side channel are coded. * *Right-side*. The right channel and side channel are coded.
Surprisingly, the left-side and right-side forms can be the most Surprisingly, the left-side and right-side forms can be the most
efficient in many frames, even though the raw number of bits per efficient in many frames, even though the raw number of bits per
sample needed for the original signal is slightly more than that sample needed for the original signal is slightly more than that
needed for independent or mid-side coding. needed for independent or mid-side coding.
9. Prediction 9. Prediction
FLAC uses four methods for modeling the input signal: FLAC uses four methods for modeling the input signal:
skipping to change at page 7, line 16 skipping to change at page 7, line 39
actually passed through the residual coding stage (it is added to actually passed through the residual coding stage (it is added to
the stream 'verbatim'), the encoding results will not be the same the stream 'verbatim'), the encoding results will not be the same
as a zero-order linear predictor. as a zero-order linear predictor.
2. *Constant*. This predictor is used whenever the subblock is pure 2. *Constant*. This predictor is used whenever the subblock is pure
DC ("digital silence"), i.e. a constant value throughout. The DC ("digital silence"), i.e. a constant value throughout. The
signal is run-length encoded and added to the stream. signal is run-length encoded and added to the stream.
3. *Fixed linear predictor*. FLAC uses a class of computationally- 3. *Fixed linear predictor*. FLAC uses a class of computationally-
efficient fixed linear predictors (for a good description, see efficient fixed linear predictors (for a good description, see
audiopak [8] and shorten [9]). FLAC adds a fourth-order audiopak (http://www.hpl.hp.com/techreports/1999/HPL-
predictor to the zero-to-third-order predictors used by Shorten. 1999-144.pdf) and shorten (http://svr-
Since the predictors are fixed, the predictor order is the only www.eng.cam.ac.uk/reports/abstracts/robinson_tr156.html)). FLAC
parameter that needs to be stored in the compressed stream. The adds a fourth-order predictor to the zero-to-third-order
error signal is then passed to the residual coder. predictors used by Shorten. Since the predictors are fixed, the
predictor order is the only parameter that needs to be stored in
the compressed stream. The error signal is then passed to the
residual coder.
4. *FIR Linear prediction*. For more accurate modeling (at a cost of 4. *FIR Linear prediction*. For more accurate modeling (at a cost of
slower encoding), FLAC supports up to 32nd order FIR linear slower encoding), FLAC supports up to 32nd order FIR linear
prediction (again, for information on linear prediction, see prediction (again, for information on linear prediction, see
audiopak [10] and shorten [11]). The reference encoder uses the audiopak (http://www.hpl.hp.com/techreports/1999/HPL-
Levinson-Durbin method for calculating the LPC coefficients from 1999-144.pdf) and shorten (http://svr-
the autocorrelation coefficients, and the coefficients are www.eng.cam.ac.uk/reports/abstracts/robinson_tr156.html)). The
quantized before computing the residual. Whereas encoders such reference encoder uses the Levinson-Durbin method for calculating
as Shorten used a fixed quantization for the entire input, FLAC the LPC coefficients from the autocorrelation coefficients, and
allows the quantized coefficient precision to vary from subframe the coefficients are quantized before computing the residual.
to subframe. The FLAC reference encoder estimates the optimal Whereas encoders such as Shorten used a fixed quantization for
precision to use based on the block size and dynamic range of the the entire input, FLAC allows the quantized coefficient precision
original signal. to vary from subframe to subframe. The FLAC reference encoder
estimates the optimal precision to use based on the block size
and dynamic range of the original signal.
10. Residual Coding 10. Residual Coding
FLAC uses Exponential-Golomb (a variant of Rice) coding as its FLAC uses Exponential-Golomb (a variant of Rice) coding as its
residual encoder. You can learn more about exp-golomb coding [12] on residual encoder. You can learn more about exp-golomb coding
(https://en.wikipedia.org/wiki/Exponential-Golomb_coding) on
Wikipedia. Wikipedia.
FLAC currently defines two similar methods for the coding of the FLAC currently defines two similar methods for the coding of the
error signal from the prediction stage. The error signal is coded error signal from the prediction stage. The error signal is coded
using Exponential-Golomb codes in one of two ways: using Exponential-Golomb codes in one of two ways:
1. the encoder estimates a single exp-golomb parameter based on the 1. the encoder estimates a single exp-golomb parameter based on the
variance of the residual and exp-golomb codes the entire residual variance of the residual and exp-golomb codes the entire residual
using this parameter; using this parameter;
skipping to change at page 8, line 12 skipping to change at page 8, line 40
contiguous samples, and each region is coded with its own exp- contiguous samples, and each region is coded with its own exp-
golomb parameter based on the region's mean. golomb parameter based on the region's mean.
(Note that the first method is a special case of the second method (Note that the first method is a special case of the second method
with one partition, except the exp-golomb parameter is based on the with one partition, except the exp-golomb parameter is based on the
residual variance instead of the mean.) residual variance instead of the mean.)
The FLAC format has reserved space for other coding methods. Some The FLAC format has reserved space for other coding methods. Some
possibilities for volunteers would be to explore better context- possibilities for volunteers would be to explore better context-
modeling of the exp-golomb parameter, or Huffman coding. See LOCO-I modeling of the exp-golomb parameter, or Huffman coding. See LOCO-I
[13] and pucrunch [14] for descriptions of several universal codes. (http://www.hpl.hp.com/techreports/98/HPL-98-193.html) and pucrunch (
http://web.archive.org/web/20140827133312/http://www.cs.tut.fi/~alber
t/Dev/pucrunch/packing.html) for descriptions of several universal
codes.
11. Format 11. Format
This section specifies the FLAC bitstream format. FLAC has no format This section specifies the FLAC bitstream format. FLAC has no format
version information, but it does contain reserved space in several version information, but it does contain reserved space in several
places. Future versions of the format MAY use this reserved space places. Future versions of the format MAY use this reserved space
safely without breaking the format of older streams. Older decoders safely without breaking the format of older streams. Older decoders
MAY choose to abort decoding or skip data encoded with newer methods. MAY choose to abort decoding or skip data encoded with newer methods.
Apart from reserved patterns, in places the format specifies invalid Apart from reserved patterns, in places the format specifies invalid
patterns, meaning that the patterns MAY never appear in any valid patterns, meaning that the patterns MAY never appear in any valid
skipping to change at page 8, line 34 skipping to change at page 9, line 25
These invalid patterns are usually used to make the synchronization These invalid patterns are usually used to make the synchronization
mechanism more robust. mechanism more robust.
All numbers used in a FLAC bitstream MUST be integers; there are no All numbers used in a FLAC bitstream MUST be integers; there are no
floating-point representations. All numbers MUST be big-endian floating-point representations. All numbers MUST be big-endian
coded. All numbers MUST be unsigned unless otherwise specified. coded. All numbers MUST be unsigned unless otherwise specified.
Before the formal description of the stream, an overview might be Before the formal description of the stream, an overview might be
helpful. helpful.
o A FLAC bitstream consists of the "fLaC" (i.e. 0x664C6143) marker * A FLAC bitstream consists of the "fLaC" (i.e. 0x664C6143) marker
at the beginning of the stream, followed by a mandatory metadata at the beginning of the stream, followed by a mandatory metadata
block (called the STREAMINFO block), any number of other metadata block (called the STREAMINFO block), any number of other metadata
blocks, then the audio frames. blocks, then the audio frames.
o FLAC supports up to 128 kinds of metadata blocks; currently the * FLAC supports up to 128 kinds of metadata blocks; currently the
following are defined: following are defined:
* "STREAMINFO": This block has information about the whole - "STREAMINFO": This block has information about the whole
stream, like sample rate, number of channels, total number of stream, like sample rate, number of channels, total number of
samples, etc. It MUST be present as the first metadata block samples, etc. It MUST be present as the first metadata block
in the stream. Other metadata blocks MAY follow, and ones that in the stream. Other metadata blocks MAY follow, and ones that
the decoder doesn't understand, it will skip. the decoder doesn't understand, it will skip.
* "PADDING": This block allows for an arbitrary amount of - "PADDING": This block allows for an arbitrary amount of
padding. The contents of a PADDING block have no meaning. padding. The contents of a PADDING block have no meaning.
This block is useful when it is known that metadata will be This block is useful when it is known that metadata will be
edited after encoding; the user can instruct the encoder to edited after encoding; the user can instruct the encoder to
reserve a PADDING block of sufficient size so that when reserve a PADDING block of sufficient size so that when
metadata is added, it will simply overwrite the padding (which metadata is added, it will simply overwrite the padding (which
is relatively quick) instead of having to insert it into the is relatively quick) instead of having to insert it into the
right place in the existing file (which would normally require right place in the existing file (which would normally require
rewriting the entire file). rewriting the entire file).
* "APPLICATION": This block is for use by third-party - "APPLICATION": This block is for use by third-party
applications. The only mandatory field is a 32-bit identifier. applications. The only mandatory field is a 32-bit identifier.
This ID is granted upon request to an application by the FLAC This ID is granted upon request to an application by the FLAC
maintainers. The remainder is of the block is defined by the maintainers. The remainder is of the block is defined by the
registered application. Visit the registration page [15] if registered application. Visit the registration page
you would like to register an ID for your application with (https://xiph.org/flac/id.html) if you would like to register
FLAC. an ID for your application with FLAC.
* "SEEKTABLE": This is an OPTIONAL block for storing seek points. - "SEEKTABLE": This is an OPTIONAL block for storing seek points.
It is possible to seek to any given sample in a FLAC stream It is possible to seek to any given sample in a FLAC stream
without a seek table, but the delay can be unpredictable since without a seek table, but the delay can be unpredictable since
the bitrate MAY vary widely within a stream. By adding seek the bitrate MAY vary widely within a stream. By adding seek
points to a stream, this delay can be significantly reduced. points to a stream, this delay can be significantly reduced.
Each seek point takes 18 bytes, so 1% resolution within a Each seek point takes 18 bytes, so 1% resolution within a
stream adds less than 2K. There can be only one SEEKTABLE in a stream adds less than 2K. There can be only one SEEKTABLE in a
stream, but the table can have any number of seek points. stream, but the table can have any number of seek points.
There is also a special 'placeholder' seekpoint which will be There is also a special 'placeholder' seekpoint which will be
ignored by decoders but which can be used to reserve space for ignored by decoders but which can be used to reserve space for
future seek point insertion. future seek point insertion.
* "VORBIS_COMMENT": This block is for storing a list of human- - "VORBIS_COMMENT": This block is for storing a list of human-
readable name/value pairs. Values are encoded using UTF-8. It readable name/value pairs. Values are encoded using UTF-8. It
is an implementation of the Vorbis comment specification [16] is an implementation of the Vorbis comment specification
(without the framing bit). This is the only officially (http://xiph.org/vorbis/doc/v-comment.html) (without the
supported tagging mechanism in FLAC. There MUST be only zero framing bit). This is the only officially supported tagging
or one VORBIS_COMMENT blocks in a stream. In some external mechanism in FLAC. There MUST be only zero or one
VORBIS_COMMENT blocks in a stream. In some external
documentation, Vorbis comments are called FLAC tags to lessen documentation, Vorbis comments are called FLAC tags to lessen
confusion. confusion.
* "CUESHEET": This block is for storing various information that - "CUESHEET": This block is for storing various information that
can be used in a cue sheet. It supports track and index can be used in a cue sheet. It supports track and index
points, compatible with Red Book CD digital audio discs, as points, compatible with Red Book CD digital audio discs, as
well as other CD-DA metadata such as media catalog number and well as other CD-DA metadata such as media catalog number and
track ISRCs. The CUESHEET block is especially useful for track ISRCs. The CUESHEET block is especially useful for
backing up CD-DA discs, but it can be used as a general purpose backing up CD-DA discs, but it can be used as a general purpose
cueing mechanism for playback. cueing mechanism for playback.
* "PICTURE": This block is for storing pictures associated with - "PICTURE": This block is for storing pictures associated with
the file, most commonly cover art from CDs. There MAY be more the file, most commonly cover art from CDs. There MAY be more
than one PICTURE block in a file. The picture format is than one PICTURE block in a file. The picture format is
similar to the APIC frame in ID3v2 [17]. The PICTURE block has similar to the APIC frame in ID3v2 (http://www.id3.org/
a type, MIME type, and UTF-8 description like ID3v2, and id3v2.4.0-frames). The PICTURE block has a type, MIME type,
supports external linking via URL (though this is discouraged). and UTF-8 description like ID3v2, and supports external linking
via URL (though this is discouraged). The differences are that
The differences are that there is no uniqueness constraint on there is no uniqueness constraint on the description field, and
the description field, and the MIME type is mandatory. The the MIME type is mandatory. The FLAC PICTURE block also
FLAC PICTURE block also includes the resolution, color depth, includes the resolution, color depth, and palette size so that
and palette size so that the client can search for a suitable the client can search for a suitable picture without having to
picture without having to scan them all. scan them all.
o The audio data is composed of one or more audio frames. Each * The audio data is composed of one or more audio frames. Each
frame consists of a frame header, which contains a sync code, frame consists of a frame header, which contains a sync code,
information about the frame like the block size, sample rate, information about the frame like the block size, sample rate,
number of channels, et cetera, and an 8-bit CRC. The frame header number of channels, et cetera, and an 8-bit CRC. The frame header
also contains either the sample number of the first sample in the also contains either the sample number of the first sample in the
frame (for variable-blocksize streams), or the frame number (for frame (for variable-blocksize streams), or the frame number (for
fixed-blocksize streams). This allows for fast, sample-accurate fixed-blocksize streams). This allows for fast, sample-accurate
seeking to be performed. Following the frame header are encoded seeking to be performed. Following the frame header are encoded
subframes, one for each channel, and finally, the frame is zero- subframes, one for each channel, and finally, the frame is zero-
padded to a byte boundary. Each subframe has its own header that padded to a byte boundary. Each subframe has its own header that
specifies how the subframe is encoded. specifies how the subframe is encoded.
o Since a decoder MAY start decoding in the middle of a stream, * Since a decoder MAY start decoding in the middle of a stream,
there MUST be a method to determine the start of a frame. A there MUST be a method to determine the start of a frame. A
14-bit sync code begins each frame. The sync code will not appear 14-bit sync code begins each frame. The sync code will not appear
anywhere else in the frame header. However, since it MAY appear anywhere else in the frame header. However, since it MAY appear
in the subframes, the decoder has two other ways of ensuring a in the subframes, the decoder has two other ways of ensuring a
correct sync. The first is to check that the rest of the frame correct sync. The first is to check that the rest of the frame
header contains no invalid data. Even this is not foolproof since header contains no invalid data. Even this is not foolproof since
valid header patterns can still occur within the subframes. The valid header patterns can still occur within the subframes. The
decoder's final check is to generate an 8-bit CRC of the frame decoder's final check is to generate an 8-bit CRC of the frame
header and compare this to the CRC stored at the end of the frame header and compare this to the CRC stored at the end of the frame
header. header.
o Again, since a decoder MAY start decoding at an arbitrary frame in * Again, since a decoder MAY start decoding at an arbitrary frame in
the stream, each frame header MUST contain some basic information the stream, each frame header MUST contain some basic information
about the stream because the decoder MAY not have access to the about the stream because the decoder MAY not have access to the
STREAMINFO metadata block at the start of the stream. This STREAMINFO metadata block at the start of the stream. This
information includes sample rate, bits per sample, number of information includes sample rate, bits per sample, number of
channels, etc. Since the frame header is pure overhead, it has a channels, etc. Since the frame header is pure overhead, it has a
direct effect on the compression ratio. To keep the frame header direct effect on the compression ratio. To keep the frame header
as small as possible, FLAC uses lookup tables for the most as small as possible, FLAC uses lookup tables for the most
commonly used values for frame parameters. For instance, the commonly used values for frame parameters. For instance, the
sample rate part of the frame header is specified using 4 bits. sample rate part of the frame header is specified using 4 bits.
Eight of the bit patterns correspond to the commonly used sample Eight of the bit patterns correspond to the commonly used sample
rates of 8, 16, 22.05, 24, 32, 44.1, 48 or 96 kHz. However, odd rates of 8, 16, 22.05, 24, 32, 44.1, 48 or 96 kHz. However, odd
sample rates can be specified by using one of the 'hint' bit sample rates can be specified by using one of the 'hint' bit
patterns, directing the decoder to find the exact sample rate at patterns, directing the decoder to find the exact sample rate at
the end of the frame header. The same method is used for the end of the frame header. The same method is used for
specifying the block size and bits per sample. In this way, the specifying the block size and bits per sample. In this way, the
frame header size stays small for all of the most common forms of frame header size stays small for all of the most common forms of
audio data. audio data.
o Individual subframes (one for each channel) are coded separately * Individual subframes (one for each channel) are coded separately
within a frame, and appear serially in the stream. In other within a frame, and appear serially in the stream. In other
words, the encoded audio data is NOT channel-interleaved. This words, the encoded audio data is NOT channel-interleaved. This
reduces decoder complexity at the cost of requiring larger decode reduces decoder complexity at the cost of requiring larger decode
buffers. Each subframe has its own header specifying the buffers. Each subframe has its own header specifying the
attributes of the subframe, like prediction method and order, attributes of the subframe, like prediction method and order,
residual coding parameters, etc. The header is followed by the residual coding parameters, etc. The header is followed by the
encoded audio data for that channel. encoded audio data for that channel.
o "FLAC" specifies a subset of itself as the Subset format. The * "FLAC" specifies a subset of itself as the Subset format. The
purpose of this is to ensure that any streams encoded according to purpose of this is to ensure that any streams encoded according to
the Subset are truly "streamable", meaning that a decoder that the Subset are truly "streamable", meaning that a decoder that
cannot seek within the stream can still pick up in the middle of cannot seek within the stream can still pick up in the middle of
the stream and start decoding. It also makes hardware decoder the stream and start decoding. It also makes hardware decoder
implementations more practical by limiting the encoding parameters implementations more practical by limiting the encoding parameters
such that decoder buffer sizes and other resource requirements can such that decoder buffer sizes and other resource requirements can
be easily determined. *flac* generates Subset streams by default be easily determined. *flac* generates Subset streams by default
unless the "--lax" command-line option is used. The Subset makes unless the "--lax" command-line option is used. The Subset makes
the following limitations on what MAY be used in the stream: the following limitations on what MAY be used in the stream:
* The blocksize bits in the "FRAME_HEADER" (see Section 11.19) * The blocksize bits in the "FRAME_HEADER" (see FRAME_HEADER section
MUST be 0b0001-0b1110. The blocksize MUST be <= 16384; if the (#frameheader)) MUST be 0b0001-0b1110. The blocksize MUST be <=
sample rate is <= 48000 Hz, the blocksize MUST be <= 4608 = 2^9 16384; if the sample rate is <= 48000 Hz, the blocksize MUST be <=
* 3^2. 4608 = 2^9 * 3^2.
* The sample rate bits in the "FRAME_HEADER" MUST be * The sample rate bits in the "FRAME_HEADER" MUST be 0b0001-0b1110.
0b0001-0b1110.
* The bits-per-sample bits in the "FRAME_HEADER" MUST be * The bits-per-sample bits in the "FRAME_HEADER" MUST be
0b001-0b111. 0b001-0b111.
* If the sample rate is <= 48000 Hz, the filter order in "LPC * If the sample rate is <= 48000 Hz, the filter order in "LPC
subframes" (see Section 11.25) MUST be less than or equal to subframes" (see SUBFRAME_LPC section (#subframelpc)) MUST be less
12, i.e. the subframe type bits in the "SUBFRAME_HEADER" (see than or equal to 12, i.e. the subframe type bits in the
Section 11.22) SHOULD NOT be 0b101100-0b111111. "SUBFRAME_HEADER" (see SUBFRAME_HEADER section (#subframeheader))
SHOULD NOT be 0b101100-0b111111.
* The Rice partition order in an "exp-golomb coded residual * The Rice partition order in an "exp-golomb coded residual section"
section" (see Section 11.27.2) MUST be less than or equal to 8. (see RESIDUAL_CODING_METHOD_PARTITIONE_EXP_GOLOMB section
(#residualcodingmethodpartitionedexpgolomb)) MUST be less than or
equal to 8.
11.1. Conventions 11.1. Conventions
The following tables constitute a formal description of the FLAC The following tables constitute a formal description of the FLAC
format. Values expressed as "u(n)" represent unsigned big-endian format. Values expressed as "u(n)" represent unsigned big-endian
integer using "n" bits. "n" may be expressed as an equation using "*" integer using "n" bits. "n" may be expressed as an equation using "*"
(multiplication), "/" (division), "+" (addition), or "-" (multiplication), "/" (division), "+" (addition), or "-"
(subtraction). An inclusive range of the number of bits expressed (subtraction). An inclusive range of the number of bits expressed
may be represented with an ellipsis, such as "u(m...n)". The name of may be represented with an ellipsis, such as "u(m...n)". The name of
a value followed by an asterisk "*" indicates zero or more a value followed by an asterisk "*" indicates zero or more
occurrences of the value. The name of a value followed by a plus occurrences of the value. The name of a value followed by a plus
sign "+" indicates one or more occurrences of the value. sign "+" indicates one or more occurrences of the value.
11.2. STREAM 11.2. STREAM
+-----------------------------+-------------------------------------+ +===========================+=====================================+
| Data | Description | | Data | Description |
+-----------------------------+-------------------------------------+ +===========================+=====================================+
| "u(32)" | "fLaC", the FLAC stream marker in | | u(32) | "fLaC", the FLAC stream marker in |
| | ASCII, meaning byte 0 of the stream | | | ASCII, meaning byte 0 of the stream |
| | is 0x66, followed by 0x4C 0x61 0x43 | | | is 0x66, followed by 0x4C 0x61 0x43 |
| "METADATA_BLOCK_STREAMINFO" | This is the mandatory STREAMINFO | +---------------------------+-------------------------------------+
| | metadata block that has the basic | | METADATA_BLOCK_STREAMINFO | This is the mandatory STREAMINFO |
| | properties of the stream. | | | metadata block that has the basic |
| "METADATA_BLOCK"* | Zero or more metadata blocks | | | properties of the stream. |
| "FRAME"+ | One or more audio frames | +---------------------------+-------------------------------------+
+-----------------------------+-------------------------------------+ | "METADATA_BLOCK"* | Zero or more metadata blocks |
+---------------------------+-------------------------------------+
| "FRAME"+ | One or more audio frames |
+---------------------------+-------------------------------------+
Table 1
11.3. METADATA_BLOCK 11.3. METADATA_BLOCK
+-------------------------+-----------------------------------------+ +=======================+========================================+
| Data | Description | | Data | Description |
+-------------------------+-----------------------------------------+ +=======================+========================================+
| "METADATA_BLOCK_HEADER" | A block header that specifies the type | | METADATA_BLOCK_HEADER | A block header that specifies the type |
| | and size of the metadata block data. | | | and size of the metadata block data. |
| "METADATA_BLOCK_DATA" | | +-----------------------+----------------------------------------+
+-------------------------+-----------------------------------------+ | METADATA_BLOCK_DATA | |
+-----------------------+----------------------------------------+
Table 2
11.4. METADATA_BLOCK_HEADER 11.4. METADATA_BLOCK_HEADER
+---------+---------------------------------------------------------+ +=======+=========================================================+
| Data | Description | | Data | Description |
+---------+---------------------------------------------------------+ +=======+=========================================================+
| "u(1)" | Last-metadata-block flag: '1' if this block is the last | | u(1) | Last-metadata-block flag: '1' if this block is the last |
| | metadata block before the audio blocks, '0' otherwise. | | | metadata block before the audio blocks, '0' otherwise. |
| "u(7)" | "BLOCK_TYPE" | +-------+---------------------------------------------------------+
| "u(24)" | Length (in bytes) of metadata to follow (does not | | u(7) | BLOCK_TYPE |
| | include the size of the "METADATA_BLOCK_HEADER") | +-------+---------------------------------------------------------+
+---------+---------------------------------------------------------+ | u(24) | Length (in bytes) of metadata to follow (does not |
| | include the size of the "METADATA_BLOCK_HEADER") |
+-------+---------------------------------------------------------+
Table 3
11.5. BLOCK_TYPE 11.5. BLOCK_TYPE
+---------+----------------------------------------------------+
+=========+====================================================+
| Value | Description | | Value | Description |
+---------+----------------------------------------------------+ +=========+====================================================+
| 0 | STREAMINFO | | 0 | STREAMINFO |
+---------+----------------------------------------------------+
| 1 | PADDING | | 1 | PADDING |
+---------+----------------------------------------------------+
| 2 | APPLICATION | | 2 | APPLICATION |
+---------+----------------------------------------------------+
| 3 | SEEKTABLE | | 3 | SEEKTABLE |
+---------+----------------------------------------------------+
| 4 | VORBIS_COMMENT | | 4 | VORBIS_COMMENT |
+---------+----------------------------------------------------+
| 5 | CUESHEET | | 5 | CUESHEET |
+---------+----------------------------------------------------+
| 6 | PICTURE | | 6 | PICTURE |
+---------+----------------------------------------------------+
| 7 - 126 | reserved | | 7 - 126 | reserved |
+---------+----------------------------------------------------+
| 127 | invalid, to avoid confusion with a frame sync code | | 127 | invalid, to avoid confusion with a frame sync code |
+---------+----------------------------------------------------+ +---------+----------------------------------------------------+
Table 4
11.6. METADATA_BLOCK_DATA 11.6. METADATA_BLOCK_DATA
+-------------------------------------------------+-----------------+ +====================================+=============+
| Data | Description | | Data | Description |
+-------------------------------------------------+-----------------+ +====================================+=============+
| "METADATA_BLOCK_STREAMINFO" || | The block data | | "METADATA_BLOCK_STREAMINFO" || | The block |
| "METADATA_BLOCK_PADDING" || | MUST match the | | "METADATA_BLOCK_PADDING" || | data MUST |
| "METADATA_BLOCK_APPLICATION" || | block type in | | "METADATA_BLOCK_APPLICATION" || | match the |
| "METADATA_BLOCK_SEEKTABLE" || | the block | | "METADATA_BLOCK_SEEKTABLE" || | block type |
| "METADATA_BLOCK_VORBIS_COMMENT" || | header. | | "METADATA_BLOCK_VORBIS_COMMENT" || | in the |
| "METADATA_BLOCK_CUESHEET" || | | | "METADATA_BLOCK_CUESHEET" || | block |
| "METADATA_BLOCK_PICTURE" | | | "METADATA_BLOCK_PICTURE" | header. |
+-------------------------------------------------+-----------------+ +------------------------------------+-------------+
Table 5
11.7. METADATA_BLOCK_STREAMINFO 11.7. METADATA_BLOCK_STREAMINFO
+----------+--------------------------------------------------------+
| Data | Description |
+----------+--------------------------------------------------------+
| "u(16)" | The minimum block size (in samples) used in the |
| | stream. |
| "u(16)" | The maximum block size (in samples) used in the |
| | stream. (Minimum blocksize == maximum blocksize) |
| | implies a fixed-blocksize stream. |
| "u(24)" | The minimum frame size (in bytes) used in the stream. |
| | A value of "0" signifies that the value is not known. |
| "u(24)" | The maximum frame size (in bytes) used in the stream. |
| | A value of "0" signifies that the value is not known. |
| "u(20)" | Sample rate in Hz. Though 20 bits are available, the |
| | maximum sample rate is limited by the structure of |
| | frame headers to 655350 Hz. Also, a value of 0 is |
| | invalid. |
| "u(3)" | (number of channels)-1. FLAC supports from 1 to 8 |
| | channels |
| "u(5)" | (bits per sample)-1. FLAC supports from 4 to 32 bits |
| | per sample. Currently the reference encoder and |
| | decoders only support up to 24 bits per sample. |
| "u(36)" | Total samples in stream. 'Samples' means inter-channel |
| | sample, i.e. one second of 44.1 kHz audio will have |
| | 44100 samples regardless of the number of channels. A |
| | value of zero here means the number of total samples |
| | is unknown. |
| "u(128)" | MD5 signature of the unencoded audio data. This allows |
| | the decoder to determine if an error exists in the |
| | audio data even when the error does not result in an |
| | invalid bitstream. |
+----------+--------------------------------------------------------+
NOTE +========+=================================================+
| Data | Description |
+========+=================================================+
| u(16) | The minimum block size (in samples) used in the |
| | stream. |
+--------+-------------------------------------------------+
| u(16) | The maximum block size (in samples) used in the |
| | stream. (Minimum blocksize == maximum |
| | blocksize) implies a fixed-blocksize stream. |
+--------+-------------------------------------------------+
| u(24) | The minimum frame size (in bytes) used in the |
| | stream. A value of "0" signifies that the |
| | value is not known. |
+--------+-------------------------------------------------+
| u(24) | The maximum frame size (in bytes) used in the |
| | stream. A value of "0" signifies that the |
| | value is not known. |
+--------+-------------------------------------------------+
| u(20) | Sample rate in Hz. Though 20 bits are |
| | available, the maximum sample rate is limited |
| | by the structure of frame headers to 655350 Hz. |
| | Also, a value of 0 is invalid. |
+--------+-------------------------------------------------+
| u(3) | (number of channels)-1. FLAC supports from 1 |
| | to 8 channels |
+--------+-------------------------------------------------+
| u(5) | (bits per sample)-1. FLAC supports from 4 to |
| | 32 bits per sample. Currently the reference |
| | encoder and decoders only support up to 24 bits |
| | per sample. |
+--------+-------------------------------------------------+
| u(36) | Total samples in stream. 'Samples' means |
| | inter-channel sample, i.e. one second of 44.1 |
| | kHz audio will have 44100 samples regardless of |
| | the number of channels. A value of zero here |
| | means the number of total samples is unknown. |
+--------+-------------------------------------------------+
| u(128) | MD5 signature of the unencoded audio data. |
| | This allows the decoder to determine if an |
| | error exists in the audio data even when the |
| | error does not result in an invalid bitstream. |
+--------+-------------------------------------------------+
o FLAC specifies a minimum block size of 16 and a maximum block size Table 6
NOTE
* FLAC specifies a minimum block size of 16 and a maximum block size
of 65535, meaning the bit patterns corresponding to the numbers of 65535, meaning the bit patterns corresponding to the numbers
0-15 in the minimum blocksize and maximum blocksize fields are 0-15 in the minimum blocksize and maximum blocksize fields are
invalid. invalid.
11.8. METADATA_BLOCK_PADDING 11.8. METADATA_BLOCK_PADDING
+--------+----------------------------------------+ +======+========================================+
| Data | Description | | Data | Description |
+--------+----------------------------------------+ +======+========================================+
| "u(n)" | n '0' bits (n MUST be a multiple of 8) | | u(n) | n '0' bits (n MUST be a multiple of 8) |
+--------+----------------------------------------+ +------+----------------------------------------+
Table 7
11.9. METADATA_BLOCK_APPLICATION 11.9. METADATA_BLOCK_APPLICATION
+---------+---------------------------------------------------------+ +=======+===========================================+
| Data | Description | | Data | Description |
+---------+---------------------------------------------------------+ +=======+===========================================+
| "u(32)" | Registered application ID. (Visit the registration page | | u(32) | Registered application ID. (Visit the |
| | [18] to register an ID with FLAC.) | | | registration page (https://xiph.org/flac/ |
| "u(n)" | Application data (n MUST be a multiple of 8) | | | id.html) to register an ID with FLAC.) |
+---------+---------------------------------------------------------+ +-------+-------------------------------------------+
| u(n) | Application data (n MUST be a multiple of |
| | 8) |
+-------+-------------------------------------------+
Table 8
11.10. METADATA_BLOCK_SEEKTABLE 11.10. METADATA_BLOCK_SEEKTABLE
+--------------+--------------------------+ +==============+==========================+
| Data | Description | | Data | Description |
+--------------+--------------------------+ +==============+==========================+
| "SEEKPOINT"+ | One or more seek points. | | "SEEKPOINT"+ | One or more seek points. |
+--------------+--------------------------+ +--------------+--------------------------+
Table 9
NOTE - The number of seek points is implied by the metadata header NOTE - The number of seek points is implied by the metadata header
'length' field, i.e. equal to length / 18. 'length' field, i.e. equal to length / 18.
11.11. SEEKPOINT 11.11. SEEKPOINT
+---------+---------------------------------------------------------+ +=======+==========================================================+
| Data | Description | | Data | Description |
+---------+---------------------------------------------------------+ +=======+==========================================================+
| "u(64)" | Sample number of first sample in the target frame, or | | u(64) | Sample number of first sample in the target frame, or |
| | "0xFFFFFFFFFFFFFFFF" for a placeholder point. | | | "0xFFFFFFFFFFFFFFFF" for a placeholder point. |
| "u(64)" | Offset (in bytes) from the first byte of the first | +-------+----------------------------------------------------------+
| | frame header to the first byte of the target frame's | | u(64) | Offset (in bytes) from the first byte of the first frame |
| | header. | | | header to the first byte of the target frame's header. |
| "u(16)" | Number of samples in the target frame. | +-------+----------------------------------------------------------+
+---------+---------------------------------------------------------+ | u(16) | Number of samples in the target frame. |
+-------+----------------------------------------------------------+
Table 10
NOTES NOTES
o For placeholder points, the second and third field values are * For placeholder points, the second and third field values are
undefined. undefined.
o Seek points within a table MUST be sorted in ascending order by * Seek points within a table MUST be sorted in ascending order by
sample number. sample number.
o Seek points within a table MUST be unique by sample number, with * Seek points within a table MUST be unique by sample number, with
the exception of placeholder points. the exception of placeholder points.
o The previous two notes imply that there MAY be any number of * The previous two notes imply that there MAY be any number of
placeholder points, but they MUST all occur at the end of the placeholder points, but they MUST all occur at the end of the
table. table.
11.12. METADATA_BLOCK_VORBIS_COMMENT 11.12. METADATA_BLOCK_VORBIS_COMMENT
+--------+----------------------------------------------------------+ +======+===========================================================+
| Data | Description | | Data | Description |
+--------+----------------------------------------------------------+ +======+===========================================================+
| "u(n)" | Also known as FLAC tags, the contents of a vorbis | | u(n) | Also known as FLAC tags, the contents of a vorbis comment |
| | comment packet as specified here [19] (without the | | | packet as specified here (http://www.xiph.org/vorbis/doc/ |
| | framing bit). Note that the vorbis comment spec allows | | | v-comment.html) (without the framing bit). Note that the |
| | for on the order of 2^64 bytes of data where as the FLAC | | | vorbis comment spec allows for on the order of 2^64 bytes |
| | metadata block is limited to 2^24 bytes. Given the | | | of data where as the FLAC metadata block is limited to |
| | stated purpose of vorbis comments, i.e. human-readable | | | 2^24 bytes. Given the stated purpose of vorbis comments, |
| | textual information, this limit is unlikely to be | | | i.e. human-readable textual information, this limit is |
| | restrictive. Also note that the 32-bit field lengths are | | | unlikely to be restrictive. Also note that the 32-bit |
| | little-endian coded according to the vorbis spec, as | | | field lengths are little-endian coded according to the |
| | opposed to the usual big-endian coding of fixed-length | | | vorbis spec, as opposed to the usual big-endian coding of |
| | integers in the rest of FLAC. | | | fixed-length integers in the rest of FLAC. |
+--------+----------------------------------------------------------+ +------+-----------------------------------------------------------+
Table 11
11.13. METADATA_BLOCK_CUESHEET 11.13. METADATA_BLOCK_CUESHEET
+-------------------+-----------------------------------------------+
| Data | Description | +===================+==============================================+
+-------------------+-----------------------------------------------+ | Data | Description |
| "u(128*8)" | Media catalog number, in ASCII printable | +===================+==============================================+
| | characters 0x20-0x7E. In general, the media | | u(128*8) | Media catalog number, in ASCII printable |
| | catalog number SHOULD be 0 to 128 bytes long; | | | characters 0x20-0x7E. In general, the media |
| | any unused characters SHOULD be right-padded | | | catalog number SHOULD be 0 to 128 bytes |
| | with NUL characters. For CD-DA, this is a | | | long; any unused characters SHOULD be right- |
| | thirteen digit number, followed by 115 NUL | | | padded with NUL characters. For CD-DA, this |
| | bytes. | | | is a thirteen digit number, followed by 115 |
| "u(64)" | The number of lead-in samples. This field has | | | NUL bytes. |
| | meaning only for CD-DA cuesheets; for other | +-------------------+----------------------------------------------+
| | uses it SHOULD be 0. For CD-DA, the lead-in | | u(64) | The number of lead-in samples. This field |
| | is the TRACK 00 area where the table of | | | has meaning only for CD-DA cuesheets; for |
| | contents is stored; more precisely, it is the | | | other uses it SHOULD be 0. For CD-DA, the |
| | number of samples from the first sample of | | | lead-in is the TRACK 00 area where the table |
| | the media to the first sample of the first | | | of contents is stored; more precisely, it is |
| | index point of the first track. According to | | | the number of samples from the first sample |
| | the Red Book, the lead-in MUST be silence and | | | of the media to the first sample of the |
| | CD grabbing software does not usually store | | | first index point of the first track. |
| | it; additionally, the lead-in MUST be at | | | According to the Red Book, the lead-in MUST |
| | least two seconds but MAY be longer. For | | | be silence and CD grabbing software does not |
| | these reasons the lead-in length is stored | | | usually store it; additionally, the lead-in |
| | here so that the absolute position of the | | | MUST be at least two seconds but MAY be |
| | first track can be computed. Note that the | | | longer. For these reasons the lead-in |
| | lead-in stored here is the number of samples | | | length is stored here so that the absolute |
| | up to the first index point of the first | | | position of the first track can be computed. |
| | track, not necessarily to INDEX 01 of the | | | Note that the lead-in stored here is the |
| | first track; even the first track MAY have | | | number of samples up to the first index |
| | INDEX 00 data. | | | point of the first track, not necessarily to |
| "u(1)" | "1" if the CUESHEET corresponds to a Compact | | | INDEX 01 of the first track; even the first |
| | Disc, else "0". | | | track MAY have INDEX 00 data. |
| "u(7+258*8)" | Reserved. All bits MUST be set to zero. | +-------------------+----------------------------------------------+
| "u(8)" | The number of tracks. Must be at least 1 | | u(1) | "1" if the CUESHEET corresponds to a Compact |
| | (because of the requisite lead-out track). | | | Disc, else "0". |
| | For CD-DA, this number MUST be no more than | +-------------------+----------------------------------------------+
| | 100 (99 regular tracks and one lead-out | | u(7+258*8) | Reserved. All bits MUST be set to zero. |
| | track). | +-------------------+----------------------------------------------+
| "CUESHEET_TRACK"+ | One or more tracks. A CUESHEET block is | | u(8) | The number of tracks. Must be at least 1 |
| | REQUIRED to have a lead-out track; it is | | | (because of the requisite lead-out track). |
| | always the last track in the CUESHEET. For | | | For CD-DA, this number MUST be no more than |
| | CD-DA, the lead-out track number MUST be 170 | | | 100 (99 regular tracks and one lead-out |
| | as specified by the Red Book, otherwise it | | | track). |
| | MUST be 255. | +-------------------+----------------------------------------------+
+-------------------+-----------------------------------------------+ | "CUESHEET_TRACK"+ | One or more tracks. A CUESHEET block is |
| | REQUIRED to have a lead-out track; it is |
| | always the last track in the CUESHEET. For |
| | CD-DA, the lead-out track number MUST be 170 |
| | as specified by the Red Book, otherwise it |
| | MUST be 255. |
+-------------------+----------------------------------------------+
Table 12
11.14. CUESHEET_TRACK 11.14. CUESHEET_TRACK
+-------------------------+-----------------------------------------+ +=======================+=================================================+
| Data | Description | |Data |Description |
+-------------------------+-----------------------------------------+ +=======================+=================================================+
| "u(64)" | Track offset in samples, relative to | |u(64) |Track offset in samples, relative to the |
| | the beginning of the FLAC audio stream. | | |beginning of the FLAC audio stream. It is the |
| | It is the offset to the first index | | |offset to the first index point of the track. |
| | point of the track. (Note how this | | |(Note how this differs from CD-DA, where the |
| | differs from CD-DA, where the track's | | |track's offset in the TOC is that of the track's |
| | offset in the TOC is that of the | | |INDEX 01 even if there is an INDEX 00.) For CD- |
| | track's INDEX 01 even if there is an | | |DA, the offset MUST be evenly divisible by 588 |
| | INDEX 00.) For CD-DA, the offset MUST | | |samples (588 samples = 44100 samples/s * 1/75 s).|
| | be evenly divisible by 588 samples (588 | +-----------------------+-------------------------------------------------+
| | samples = 44100 samples/s * 1/75 s). | |u(8) |Track number. A track number of 0 is not allowed|
| "u(8)" | Track number. A track number of 0 is | | |to avoid conflicting with the CD-DA spec, which |
| | not allowed to avoid conflicting with | | |reserves this for the lead-in. For CD-DA the |
| | the CD-DA spec, which reserves this for | | |number MUST be 1-99, or 170 for the lead-out; for|
| | the lead-in. For CD-DA the number MUST | | |non-CD-DA, the track number MUST for 255 for the |
| | be 1-99, or 170 for the lead-out; for | | |lead-out. It is not REQUIRED but encouraged to |
| | non-CD-DA, the track number MUST for | | |start with track 1 and increase sequentially. |
| | 255 for the lead-out. It is not | | |Track numbers MUST be unique within a CUESHEET. |
| | REQUIRED but encouraged to start with | +-----------------------+-------------------------------------------------+
| | track 1 and increase sequentially. | |u(12*8) |Track ISRC. This is a 12-digit alphanumeric |
| | Track numbers MUST be unique within a | | |code; see here (http://isrc.ifpi.org/) and here |
| | CUESHEET. | | |(http://www.disctronics.co.uk/technology/cdaudio/|
| "u(12*8)" | Track ISRC. This is a 12-digit | | |cdaud_isrc.htm). A value of 12 ASCII NUL |
| | alphanumeric code; see here [20] and | | |characters MAY be used to denote absence of an |
| | here [21]. A value of 12 ASCII NUL | | |ISRC. |
| | characters MAY be used to denote | +-----------------------+-------------------------------------------------+
| | absence of an ISRC. | |u(1) |The track type: 0 for audio, 1 for non-audio. |
| "u(1)" | The track type: 0 for audio, 1 for non- | | |This corresponds to the CD-DA Q-channel control |
| | audio. This corresponds to the CD-DA | | |bit 3. |
| | Q-channel control bit 3. | +-----------------------+-------------------------------------------------+
| "u(1)" | The pre-emphasis flag: 0 for no pre- | |u(1) |The pre-emphasis flag: 0 for no pre-emphasis, 1 |
| | emphasis, 1 for pre-emphasis. This | | |for pre-emphasis. This corresponds to the CD-DA |
| | corresponds to the CD-DA Q-channel | | |Q-channel control bit 5; see here |
| | control bit 5; see here [22]. | | |(http://www.chipchapin.com/CDMedia/cdda9.php3). |
| "u(6+13*8)" | Reserved. All bits MUST be set to zero. | +-----------------------+-------------------------------------------------+
| "u(8)" | The number of track index points. There | |u(6+13*8) |Reserved. All bits MUST be set to zero. |
| | MUST be at least one index in every | +-----------------------+-------------------------------------------------+
| | track in a CUESHEET except for the | |u(8) |The number of track index points. There MUST be |
| | lead-out track, which MUST have zero. | | |at least one index in every track in a CUESHEET |
| | For CD-DA, this number SHOULD NOT be | | |except for the lead-out track, which MUST have |
| | more than 100. | | |zero. For CD-DA, this number SHOULD NOT be more |
| "CUESHEET_TRACK_INDEX"+ | For all tracks except the lead-out | | |than 100. |
| | track, one or more track index points. | +-----------------------+-------------------------------------------------+
+-------------------------+-----------------------------------------+ |"CUESHEET_TRACK_INDEX"+|For all tracks except the lead-out track, one or |
| |more track index points. |
+-----------------------+-------------------------------------------------+
Table 13
11.15. CUESHEET_TRACK_INDEX 11.15. CUESHEET_TRACK_INDEX
+----------+--------------------------------------------------------+ +========+=========================================================+
| Data | Description | | Data | Description |
+----------+--------------------------------------------------------+ +========+=========================================================+
| "u(64)" | Offset in samples, relative to the track offset, of | | u(64) | Offset in samples, relative to the track offset, of the |
| | the index point. For CD-DA, the offset MUST be evenly | | | index point. For CD-DA, the offset MUST be evenly |
| | divisible by 588 samples (588 samples = 44100 | | | divisible by 588 samples (588 samples = 44100 samples/s |
| | samples/s * 1/75 s). Note that the offset is from the | | | * 1/75 s). Note that the offset is from the beginning |
| | beginning of the track, not the beginning of the audio | | | of the track, not the beginning of the audio data. |
| | data. | +--------+---------------------------------------------------------+
| "u(8)" | The index point number. For CD-DA, an index number of | | u(8) | The index point number. For CD-DA, an index number of |
| | 0 corresponds to the track pre-gap. The first index in | | | 0 corresponds to the track pre-gap. The first index in |
| | a track MUST have a number of 0 or 1, and | | | a track MUST have a number of 0 or 1, and subsequently, |
| | subsequently, index numbers MUST increase by 1. Index | | | index numbers MUST increase by 1. Index numbers MUST |
| | numbers MUST be unique within a track. | | | be unique within a track. |
| "u(3*8)" | Reserved. All bits MUST be set to zero. | +--------+---------------------------------------------------------+
+----------+--------------------------------------------------------+ | u(3*8) | Reserved. All bits MUST be set to zero. |
+--------+---------------------------------------------------------+
Table 14
11.16. METADATA_BLOCK_PICTURE 11.16. METADATA_BLOCK_PICTURE
+----------+--------------------------------------------------------+ +========+==================================================+
| Data | Description | | Data | Description |
+----------+--------------------------------------------------------+ +========+==================================================+
| "u(32)" | The PICTURE_TYPE according to the ID3v2 APIC frame. | | u(32) | The PICTURE_TYPE according to the ID3v2 APIC |
| "u(32)" | The length of the MIME type string in bytes. | | | frame. |
| "u(n*8)" | The MIME type string, in printable ASCII characters | +--------+--------------------------------------------------+
| | 0x20-0x7E. The MIME type MAY also be "-->" to signify | | u(32) | The length of the MIME type string in bytes. |
| | that the data part is a URL of the picture instead of | +--------+--------------------------------------------------+
| | the picture data itself. | | u(n*8) | The MIME type string, in printable ASCII |
| "u(32)" | The length of the description string in bytes. | | | characters 0x20-0x7E. The MIME type MAY also be |
| "u(n*8)" | The description of the picture, in UTF-8. | | | "-->" to signify that the data part is a URL of |
| "u(32)" | The width of the picture in pixels. | | | the picture instead of the picture data itself. |
| "u(32)" | The height of the picture in pixels. | +--------+--------------------------------------------------+
| "u(32)" | The color depth of the picture in bits-per-pixel. | | u(32) | The length of the description string in bytes. |
| "u(32)" | For indexed-color pictures (e.g. GIF), the number of | +--------+--------------------------------------------------+
| | colors used, or "0" for non-indexed pictures. | | u(n*8) | The description of the picture, in UTF-8. |
| "u(32)" | The length of the picture data in bytes. | +--------+--------------------------------------------------+
| "u(n*8)" | The binary picture data. | | u(32) | The width of the picture in pixels. |
+----------+--------------------------------------------------------+ +--------+--------------------------------------------------+
| u(32) | The height of the picture in pixels. |
+--------+--------------------------------------------------+
| u(32) | The color depth of the picture in bits-per- |
| | pixel. |
+--------+--------------------------------------------------+
| u(32) | For indexed-color pictures (e.g. GIF), the |
| | number of colors used, or "0" for non-indexed |
| | pictures. |
+--------+--------------------------------------------------+
| u(32) | The length of the picture data in bytes. |
+--------+--------------------------------------------------+
| u(n*8) | The binary picture data. |
+--------+--------------------------------------------------+
Table 15
11.17. PICTURE_TYPE 11.17. PICTURE_TYPE
+-------+-------------------------------------+
+=======+=====================================+
| Value | Description | | Value | Description |
+-------+-------------------------------------+ +=======+=====================================+
| 0 | Other | | 0 | Other |
+-------+-------------------------------------+
| 1 | 32x32 pixels 'file icon' (PNG only) | | 1 | 32x32 pixels 'file icon' (PNG only) |
+-------+-------------------------------------+
| 2 | Other file icon | | 2 | Other file icon |
+-------+-------------------------------------+
| 3 | Cover (front) | | 3 | Cover (front) |
+-------+-------------------------------------+
| 4 | Cover (back) | | 4 | Cover (back) |
+-------+-------------------------------------+
| 5 | Leaflet page | | 5 | Leaflet page |
+-------+-------------------------------------+
| 6 | Media (e.g. label side of CD) | | 6 | Media (e.g. label side of CD) |
+-------+-------------------------------------+
| 7 | Lead artist/lead performer/soloist | | 7 | Lead artist/lead performer/soloist |
+-------+-------------------------------------+
| 8 | Artist/performer | | 8 | Artist/performer |
+-------+-------------------------------------+
| 9 | Conductor | | 9 | Conductor |
+-------+-------------------------------------+
| 10 | Band/Orchestra | | 10 | Band/Orchestra |
+-------+-------------------------------------+
| 11 | Composer | | 11 | Composer |
+-------+-------------------------------------+
| 12 | Lyricist/text writer | | 12 | Lyricist/text writer |
+-------+-------------------------------------+
| 13 | Recording Location | | 13 | Recording Location |
+-------+-------------------------------------+
| 14 | During recording | | 14 | During recording |
+-------+-------------------------------------+
| 15 | During performance | | 15 | During performance |
+-------+-------------------------------------+
| 16 | Movie/video screen capture | | 16 | Movie/video screen capture |
+-------+-------------------------------------+
| 17 | A bright colored fish | | 17 | A bright colored fish |
+-------+-------------------------------------+
| 18 | Illustration | | 18 | Illustration |
+-------+-------------------------------------+
| 19 | Band/artist logotype | | 19 | Band/artist logotype |
+-------+-------------------------------------+
| 20 | Publisher/Studio logotype | | 20 | Publisher/Studio logotype |
+-------+-------------------------------------+ +-------+-------------------------------------+
Table 16
Other values are reserved and SHOULD NOT be used. There MAY only be Other values are reserved and SHOULD NOT be used. There MAY only be
one each of picture type 1 and 2 in a file. one each of picture type 1 and 2 in a file.
11.18. FRAME 11.18. FRAME
+----------------+---------------------------------+ +==============+=================================+
| Data | Description | | Data | Description |
+----------------+---------------------------------+ +==============+=================================+
| "FRAME_HEADER" | | | FRAME_HEADER | |
| "SUBFRAME"+ | One SUBFRAME per channel. | +--------------+---------------------------------+
| "u(?)" | Zero-padding to byte alignment. | | "SUBFRAME"+ | One SUBFRAME per channel. |
| "FRAME_FOOTER" | | +--------------+---------------------------------+
+----------------+---------------------------------+ | u(?) | Zero-padding to byte alignment. |
+--------------+---------------------------------+
| FRAME_FOOTER | |
+--------------+---------------------------------+
Table 17
11.19. FRAME_HEADER 11.19. FRAME_HEADER
+---------+----------------------------------+
| Data | Description | +=======+================================+
+---------+----------------------------------+ | Data | Description |
| "u(14)" | Sync code '0b11111111111110' | +=======+================================+
| "u(1)" | "FRAME HEADER RESERVED" | | u(14) | Sync code '0b11111111111110' |
| "u(1)" | "BLOCKING STRATEGY" | +-------+--------------------------------+
| "u(4)" | "INTERCHANNEL SAMPLE BLOCK SIZE" | | u(1) | FRAME HEADER RESERVED |
| "u(4)" | "SAMPLE RATE" | +-------+--------------------------------+
| "u(4)" | "CHANNEL ASSIGNMENT" | | u(1) | BLOCKING STRATEGY |
| "u(3)" | "SAMPLE SIZE" | +-------+--------------------------------+
| "u(1)" | "FRAME HEADER RESERVED2" | | u(4) | INTERCHANNEL SAMPLE BLOCK SIZE |
| "u(?)" | "CODED NUMBER" | +-------+--------------------------------+
| "u(?)" | "BLOCK SIZE INT" | | u(4) | SAMPLE RATE |
| "u(?)" | "SAMPLE RATE INT" | +-------+--------------------------------+
| "u(8)" | "FRAME CRC" | | u(4) | CHANNEL ASSIGNMENT |
+---------+----------------------------------+ +-------+--------------------------------+
| u(3) | SAMPLE SIZE |
+-------+--------------------------------+
| u(1) | FRAME HEADER RESERVED2 |
+-------+--------------------------------+
| u(?) | CODED NUMBER |
+-------+--------------------------------+
| u(?) | BLOCK SIZE INT |
+-------+--------------------------------+
| u(?) | SAMPLE RATE INT |
+-------+--------------------------------+
| u(8) | FRAME CRC |
+-------+--------------------------------+
Table 18
11.19.1. FRAME HEADER RESERVED 11.19.1. FRAME HEADER RESERVED
+-------+-------------------------+ +=======+=========================+
| Value | Description | | Value | Description |
+-------+-------------------------+ +=======+=========================+
| 0 | mandatory value | | 0 | mandatory value |
+-------+-------------------------+
| 1 | reserved for future use | | 1 | reserved for future use |
+-------+-------------------------+ +-------+-------------------------+
Table 19
FRAME HEADER RESERVED MUST remain reserved for "0" in order for a FRAME HEADER RESERVED MUST remain reserved for "0" in order for a
FLAC frame's initial 15 bits to be distinguishable from the start of FLAC frame's initial 15 bits to be distinguishable from the start of
an MPEG audio frame (see also [23]). an MPEG audio frame (see also (http://lists.xiph.org/pipermail/flac-
dev/2008-December/002607.html)).
11.19.2. BLOCKING STRATEGY 11.19.2. BLOCKING STRATEGY
+-------+-----------------------------------------------------------+ +=======+==================================+
| Value | Description | | Value | Description |
+-------+-----------------------------------------------------------+ +=======+==================================+
| 0 | fixed-blocksize stream; frame header encodes the frame | | 0 | fixed-blocksize stream; frame |
| | number | | | header encodes the frame number |
| 1 | variable-blocksize stream; frame header encodes the | +-------+----------------------------------+
| | sample number | | 1 | variable-blocksize stream; frame |
+-------+-----------------------------------------------------------+ | | header encodes the sample number |
+-------+----------------------------------+
Table 20
The "BLOCKING STRATEGY" bit MUST be the same throughout the entire The "BLOCKING STRATEGY" bit MUST be the same throughout the entire
stream. stream.
The "BLOCKING STRATEGY" bit determines how to calculate the sample The "BLOCKING STRATEGY" bit determines how to calculate the sample
number of the first sample in the frame. If the bit is "0" (fixed- number of the first sample in the frame. If the bit is "0" (fixed-
blocksize), the frame header encodes the frame number as above, and blocksize), the frame header encodes the frame number as above, and
the frame's starting sample number will be the frame number times the the frame's starting sample number will be the frame number times the
blocksize. If it is "1" (variable-blocksize), the frame header blocksize. If it is "1" (variable-blocksize), the frame header
encodes the frame's starting sample number itself. (In the case of a encodes the frame's starting sample number itself. (In the case of a
fixed-blocksize stream, only the last block MAY be shorter than the fixed-blocksize stream, only the last block MAY be shorter than the
stream blocksize; its starting sample number will be calculated as stream blocksize; its starting sample number will be calculated as
the frame number times the previous frame's blocksize, or zero if it the frame number times the previous frame's blocksize, or zero if it
is the first frame). is the first frame).
11.19.3. INTERCHANNEL SAMPLE BLOCK SIZE 11.19.3. INTERCHANNEL SAMPLE BLOCK SIZE
+-------------+-----------------------------------------------------+ +=================+=========================================+
| Value | Description | | Value | Description |
+-------------+-----------------------------------------------------+ +=================+=========================================+
| 0b0000 | reserved | | 0b0000 | reserved |
| 0b0001 | 192 samples | +-----------------+-----------------------------------------+
| 0b0010 - | 576 * (2^(n-2)) samples, i.e. 576, 1152, 2304 or | | 0b0001 | 192 samples |
| 0b0101 | 4608 | +-----------------+-----------------------------------------+
| 0b0110 | get 8 bit (blocksize-1) from end of header | | 0b0010 - 0b0101 | 576 * (2^(n-2)) samples, i.e. 576, |
| 0b0111 | get 16 bit (blocksize-1) from end of header | | | 1152, 2304 or 4608 |
| 0b1000 - | 256 * (2^(n-8)) samples, i.e. 256, 512, 1024, 2048, | +-----------------+-----------------------------------------+
| 0b1111 | 4096, 8192, 16384 or 32768 | | 0b0110 | get 8 bit (blocksize-1) from end of |
+-------------+-----------------------------------------------------+ | | header |
+-----------------+-----------------------------------------+
| 0b0111 | get 16 bit (blocksize-1) from end of |
| | header |
+-----------------+-----------------------------------------+
| 0b1000 - 0b1111 | 256 * (2^(n-8)) samples, i.e. 256, 512, |
| | 1024, 2048, 4096, 8192, 16384 or 32768 |
+-----------------+-----------------------------------------+
Table 21
11.19.4. SAMPLE RATE 11.19.4. SAMPLE RATE
+--------+-----------------------------------------------------+ +========+=====================================================+
| Value | Description | | Value | Description |
+--------+-----------------------------------------------------+ +========+=====================================================+
| 0b0000 | get from STREAMINFO metadata block | | 0b0000 | get from STREAMINFO metadata block |
+--------+-----------------------------------------------------+
| 0b0001 | 88.2 kHz | | 0b0001 | 88.2 kHz |
+--------+-----------------------------------------------------+
| 0b0010 | 176.4 kHz | | 0b0010 | 176.4 kHz |
+--------+-----------------------------------------------------+
| 0b0011 | 192 kHz | | 0b0011 | 192 kHz |
+--------+-----------------------------------------------------+
| 0b0100 | 8 kHz | | 0b0100 | 8 kHz |
+--------+-----------------------------------------------------+
| 0b0101 | 16 kHz | | 0b0101 | 16 kHz |
+--------+-----------------------------------------------------+
| 0b0110 | 22.05 kHz | | 0b0110 | 22.05 kHz |
+--------+-----------------------------------------------------+
| 0b0111 | 24 kHz | | 0b0111 | 24 kHz |
+--------+-----------------------------------------------------+
| 0b1000 | 32 kHz | | 0b1000 | 32 kHz |
+--------+-----------------------------------------------------+
| 0b1001 | 44.1 kHz | | 0b1001 | 44.1 kHz |
+--------+-----------------------------------------------------+
| 0b1010 | 48 kHz | | 0b1010 | 48 kHz |
+--------+-----------------------------------------------------+
| 0b1011 | 96 kHz | | 0b1011 | 96 kHz |
+--------+-----------------------------------------------------+
| 0b1100 | get 8 bit sample rate (in kHz) from end of header | | 0b1100 | get 8 bit sample rate (in kHz) from end of header |
+--------+-----------------------------------------------------+
| 0b1101 | get 16 bit sample rate (in Hz) from end of header | | 0b1101 | get 16 bit sample rate (in Hz) from end of header |
+--------+-----------------------------------------------------+
| 0b1110 | get 16 bit sample rate (in daHz) from end of header | | 0b1110 | get 16 bit sample rate (in daHz) from end of header |
+--------+-----------------------------------------------------+
| 0b1111 | invalid, to prevent sync-fooling string of 1s | | 0b1111 | invalid, to prevent sync-fooling string of 1s |
+--------+-----------------------------------------------------+ +--------+-----------------------------------------------------+
Table 22
11.19.5. CHANNEL ASSIGNMENT 11.19.5. CHANNEL ASSIGNMENT
For values 0b0000-0b0111, the value represents the (number of For values 0b0000-0b0111, the value represents the (number of
independent channels)-1. Where defined, the channel order follows independent channels)-1. Where defined, the channel order follows
SMPTE/ITU-R recommendations. SMPTE/ITU-R recommendations.
+-----------+-------------------------------------------------------+ +==========+======================================================+
| Value | Description | | Value | Description |
+-----------+-------------------------------------------------------+ +==========+======================================================+
| 0b0000 | 1 channel: mono | | 0b0000 | 1 channel: mono |
| 0b0001 | 2 channels: left, right | +----------+------------------------------------------------------+
| 0b0010 | 3 channels: left, right, center | | 0b0001 | 2 channels: left, right |
| 0b0011 | 4 channels: front left, front right, back left, back | +----------+------------------------------------------------------+
| | right | | 0b0010 | 3 channels: left, right, center |
| 0b0100 | 5 channels: front left, front right, front center, | +----------+------------------------------------------------------+
| | back/surround left, back/surround right | | 0b0011 | 4 channels: front left, front right, back left, back |
| 0b0101 | 6 channels: front left, front right, front center, | | | right |
| | LFE, back/surround left, back/surround right | +----------+------------------------------------------------------+
| 0b0110 | 7 channels: front left, front right, front center, | | 0b0100 | 5 channels: front left, front right, front center, |
| | LFE, back center, side left, side right | | | back/surround left, back/surround right |
| 0b0111 | 8 channels: front left, front right, front center, | +----------+------------------------------------------------------+
| | LFE, back left, back right, side left, side right | | 0b0101 | 6 channels: front left, front right, front center, |
| 0b1000 | left/side stereo: channel 0 is the left channel, | | | LFE, back/surround left, back/surround right |
| | channel 1 is the side(difference) channel | +----------+------------------------------------------------------+
| 0b1001 | right/side stereo: channel 0 is the side(difference) | | 0b0110 | 7 channels: front left, front right, front center, |
| | channel, channel 1 is the right channel | | | LFE, back center, side left, side right |
| 0b1010 | mid/side stereo: channel 0 is the mid(average) | +----------+------------------------------------------------------+
| | channel, channel 1 is the side(difference) channel | | 0b0111 | 8 channels: front left, front right, front center, |
| 0b1011 - | reserved | | | LFE, back left, back right, side left, side right |
| 0b1111 | | +----------+------------------------------------------------------+
+-----------+-------------------------------------------------------+ | 0b1000 | left/side stereo: channel 0 is the left channel, |
| | channel 1 is the side(difference) channel |
+----------+------------------------------------------------------+
| 0b1001 | right/side stereo: channel 0 is the side(difference) |
| | channel, channel 1 is the right channel |
+----------+------------------------------------------------------+
| 0b1010 | mid/side stereo: channel 0 is the mid(average) |
| | channel, channel 1 is the side(difference) channel |
+----------+------------------------------------------------------+
| 0b1011 - | reserved |
| 0b1111 | |
+----------+------------------------------------------------------+
Table 23
11.19.6. SAMPLE SIZE 11.19.6. SAMPLE SIZE
+-------+------------------------------------+ +=======+====================================+
| Value | Description | | Value | Description |
+-------+------------------------------------+ +=======+====================================+
| 0b000 | get from STREAMINFO metadata block | | 0b000 | get from STREAMINFO metadata block |
+-------+------------------------------------+
| 0b001 | 8 bits per sample | | 0b001 | 8 bits per sample |
+-------+------------------------------------+
| 0b010 | 12 bits per sample | | 0b010 | 12 bits per sample |
+-------+------------------------------------+
| 0b011 | reserved | | 0b011 | reserved |
+-------+------------------------------------+
| 0b100 | 16 bits per sample | | 0b100 | 16 bits per sample |
+-------+------------------------------------+
| 0b101 | 20 bits per sample | | 0b101 | 20 bits per sample |
+-------+------------------------------------+
| 0b110 | 24 bits per sample | | 0b110 | 24 bits per sample |
+-------+------------------------------------+
| 0b111 | reserved | | 0b111 | reserved |
+-------+------------------------------------+ +-------+------------------------------------+
Table 24
For subframes that encode a difference channel, the sample size is For subframes that encode a difference channel, the sample size is
one bit larger than the sample size of the frame, in order to be able one bit larger than the sample size of the frame, in order to be able
to encode the difference between extreme values. to encode the difference between extreme values.
11.19.7. FRAME HEADER RESERVED2 11.19.7. FRAME HEADER RESERVED2
+-------+-------------------------+ +=======+=========================+
| Value | Description | | Value | Description |
+-------+-------------------------+ +=======+=========================+
| 0 | mandatory value | | 0 | mandatory value |
+-------+-------------------------+
| 1 | reserved for future use | | 1 | reserved for future use |
+-------+-------------------------+ +-------+-------------------------+
Table 25
11.19.8. CODED NUMBER 11.19.8. CODED NUMBER
Frame/Sample numbers are encoded using the UTF-8 format, from BEFORE Frame/Sample numbers are encoded using the UTF-8 format, from BEFORE
it was limited to 4 bytes by RFC3629, this variant supports the it was limited to 4 bytes by RFC3629, this variant supports the
original 7 byte maximum. original 7 byte maximum.
Note to implementors: All Unicode compliant UTF-8 decoders and Note to implementors: All Unicode compliant UTF-8 decoders and
encoders are limited to 4 bytes, it's best to just write your own one encoders are limited to 4 bytes, it's best to just write your own one
off solution. off solution.
if(variable blocksize) if(variable blocksize)
`u(8...56)`: "UTF-8" coded sample number (decoded number is 36 bits) `u(8...56)`: "UTF-8" coded sample number (decoded number is 36 bits)
else else
`u(8...48)`: "UTF-8" coded frame number (decoded number is 31 bits) `u(8...48)`: "UTF-8" coded frame number (decoded number is 31 bits)
11.19.9. BLOCK SIZE INT 11.19.9. BLOCK SIZE INT
if(`INTERCHANNEL SAMPLE BLOCK SIZE` == 0b0110) if(`INTERCHANNEL SAMPLE BLOCK SIZE` == 0b0110)
8 bit (blocksize-1) 8 bit (blocksize-1)
else if(`INTERCHANNEL SAMPLE BLOCK SIZE` == 0b0111) else if(`INTERCHANNEL SAMPLE BLOCK SIZE` == 0b0111)
16 bit (blocksize-1) 16 bit (blocksize-1)
11.19.10. SAMPLE RATE INT 11.19.10. SAMPLE RATE INT
if(`SAMPLE RATE` == 0b1100) if(`SAMPLE RATE` == 0b1100)
8 bit sample rate (in kHz) 8 bit sample rate (in kHz)
else if(`SAMPLE RATE` == 0b1101) else if(`SAMPLE RATE` == 0b1101)
16 bit sample rate (in Hz) 16 bit sample rate (in Hz)
else if(`SAMPLE RATE` == 0b1110) else if(`SAMPLE RATE` == 0b1110)
16 bit sample rate (in daHz) 16 bit sample rate (in daHz)
11.19.11. FRAME CRC 11.19.11. FRAME CRC
CRC-8 (polynomial = x^8 + x^2 + x^1 + x^0, initialized with 0) of CRC-8 (polynomial = x^8 + x^2 + x^1 + x^0, initialized with 0) of
everything before the CRC, including the sync code everything before the CRC, including the sync code
11.20. FRAME_FOOTER 11.20. FRAME_FOOTER
+---------+---------------------------------------------------------+ +=======+===================================================+
| Data | Description | | Data | Description |
+---------+---------------------------------------------------------+ +=======+===================================================+
| "u(16)" | CRC-16 (polynomial = x^16 + x^15 + x^2 + x^0, | | u(16) | CRC-16 (polynomial = x^16 + x^15 + x^2 + x^0, |
| | initialized with 0) of everything before the CRC, back | | | initialized with 0) of everything before the CRC, |
| | to and including the frame header sync code | | | back to and including the frame header sync code |
+---------+---------------------------------------------------------+ +-------+---------------------------------------------------+
Table 26
11.21. SUBFRAME 11.21. SUBFRAME
+-------------------------------------------+-----------------------+ +============================================+======================+
| Data | Description | | Data | Description |
+-------------------------------------------+-----------------------+ +============================================+======================+
| "SUBFRAME_HEADER" | | | SUBFRAME_HEADER | |
| "SUBFRAME_CONSTANT" || "SUBFRAME_FIXED" | The SUBFRAME_HEADER | +--------------------------------------------+----------------------+
| || "SUBFRAME_LPC" || "SUBFRAME_VERBATIM" | specifies which one. | | "SUBFRAME_CONSTANT" || "SUBFRAME_FIXED" || | The SUBFRAME_HEADER |
+-------------------------------------------+-----------------------+ | "SUBFRAME_LPC" || "SUBFRAME_VERBATIM" | specifies which |
| | one. |
+--------------------------------------------+----------------------+
Table 27
11.22. SUBFRAME_HEADER 11.22. SUBFRAME_HEADER
+----------+--------------------------------------------------------+ +========+========================================================+
| Data | Description | | Data | Description |
+----------+--------------------------------------------------------+ +========+========================================================+
| "u(1)" | Zero bit padding, to prevent sync-fooling string of 1s | | u(1) | Zero bit padding, to prevent sync-fooling string of 1s |
| "u(6)" | "SUBFRAME TYPE" (see Section 11.22.1) | +--------+--------------------------------------------------------+
| "u(1+k)" | "WASTED BITS PER SAMPLE FLAG" (see Section 11.22.2) | | u(6) | "SUBFRAME TYPE" (see section on SUBFRAME TYPE |
+----------+--------------------------------------------------------+ | | (#subframe-type)) |
+--------+--------------------------------------------------------+
| u(1+k) | "WASTED BITS PER SAMPLE FLAG" (see section on WASTED |
| | BITS PER SAMPLE FLAG (#wasted-bits-per-sample-flag)) |
+--------+--------------------------------------------------------+
Table 28
11.22.1. SUBFRAME TYPE 11.22.1. SUBFRAME TYPE
+----------+--------------------------------------------------------+
| Value | Description | +==========+================================+
+----------+--------------------------------------------------------+ | Value | Description |
| 0b000000 | "SUBFRAME_CONSTANT" | +==========+================================+
| 0b000001 | "SUBFRAME_VERBATIM" | | 0b000000 | SUBFRAME_CONSTANT |
| 0b00001x | reserved | +----------+--------------------------------+
| 0b0001xx | reserved | | 0b000001 | SUBFRAME_VERBATIM |
| 0b001xxx | if(xxx <= 4) "SUBFRAME_FIXED", xxx=order; else | +----------+--------------------------------+
| | reserved | | 0b00001x | reserved |
| 0b01xxxx | reserved | +----------+--------------------------------+
| 0b1xxxxx | "SUBFRAME_LPC", xxxxx=order-1 | | 0b0001xx | reserved |
+----------+--------------------------------------------------------+ +----------+--------------------------------+
| 0b001xxx | if(xxx <= 4) "SUBFRAME_FIXED", |
| | xxx=order; else reserved |
+----------+--------------------------------+
| 0b01xxxx | reserved |
+----------+--------------------------------+
| 0b1xxxxx | "SUBFRAME_LPC", xxxxx=order-1 |
+----------+--------------------------------+
Table 29
11.22.2. WASTED BITS PER SAMPLE FLAG 11.22.2. WASTED BITS PER SAMPLE FLAG
+-------+-----------------------------------------------------------+ +=======+==============================================+
| Value | Description | | Value | Description |
+-------+-----------------------------------------------------------+ +=======+==============================================+
| 0 | no wasted bits-per-sample in source subblock, k=0 | | 0 | no wasted bits-per-sample in source |
| 1 | k wasted bits-per-sample in source subblock, k-1 follows, | | | subblock, k=0 |
| | unary coded; e.g. k=3 => 0b001 follows, k=7 => 0b0000001 | +-------+----------------------------------------------+
| | follows. | | 1 | k wasted bits-per-sample in source subblock, |
+-------+-----------------------------------------------------------+ | | k-1 follows, unary coded; e.g. k=3 => 0b001 |
| | follows, k=7 => 0b0000001 follows. |
+-------+----------------------------------------------+
Table 30
The size of the samples stored in the subframe is the subframe sample The size of the samples stored in the subframe is the subframe sample
size reduced by k bits. Decoded samples must be shifted left by k size reduced by k bits. Decoded samples must be shifted left by k
bits. bits.
11.23. SUBFRAME_CONSTANT 11.23. SUBFRAME_CONSTANT
+--------+----------------------------------------------------------+ +======+========================================+
| Data | Description | | Data | Description |
+--------+----------------------------------------------------------+ +======+========================================+
| "u(n)" | Unencoded constant value of the subblock, n = frame's | | u(n) | Unencoded constant value of the |
| | bits-per-sample. | | | subblock, n = frame's bits-per-sample. |
+--------+----------------------------------------------------------+ +------+----------------------------------------+
Table 31
11.24. SUBFRAME_FIXED 11.24. SUBFRAME_FIXED
+------------+------------------------------------------------------+ +==========+========================================+
| Data | Description | | Data | Description |
+------------+------------------------------------------------------+ +==========+========================================+
| "u(n)" | Unencoded warm-up samples (n = frame's bits-per- | | u(n) | Unencoded warm-up samples (n = frame's |
| | sample * predictor order). | | | bits-per-sample * predictor order). |
| "RESIDUAL" | Encoded residual | +----------+----------------------------------------+
+------------+------------------------------------------------------+ | RESIDUAL | Encoded residual |
+----------+----------------------------------------+
Table 32
11.25. SUBFRAME_LPC 11.25. SUBFRAME_LPC
+------------+------------------------------------------------------+ +==========+========================================================+
| Data | Description | | Data | Description |
+------------+------------------------------------------------------+ +==========+========================================================+
| "u(n)" | Unencoded warm-up samples (n = frame's bits-per- | | u(n) | Unencoded warm-up samples (n = frame's bits- |
| | sample * lpc order). | | | per-sample * lpc order). |
| "u(4)" | (quantized linear predictor coefficients' precision | +----------+--------------------------------------------------------+
| | in bits)-1 (NOTE: 0b1111 is invalid). | | u(4) | (quantized linear predictor coefficients' |
| "u(5)" | Quantized linear predictor coefficient shift needed | | | precision in bits)-1 (NOTE: 0b1111 is invalid). |
| | in bits (NOTE: this number is signed | +----------+--------------------------------------------------------+
| | two's-complement). | | u(5) | Quantized linear predictor coefficient shift |
| "u(n)" | Unencoded predictor coefficients (n = qlp coeff | | | needed in bits (NOTE: this number is signed |
| | precision * lpc order) (NOTE: the coefficients are | | | two's-complement). |
| | signed two's-complement). | +----------+--------------------------------------------------------+
| "RESIDUAL" | Encoded residual | | u(n) | Unencoded predictor coefficients (n = qlp coeff |
+------------+------------------------------------------------------+ | | precision * lpc order) (NOTE: the coefficients |
| | are signed two's-complement). |
+----------+--------------------------------------------------------+
| RESIDUAL | Encoded residual |
+----------+--------------------------------------------------------+
Table 33
11.26. SUBFRAME_VERBATIM 11.26. SUBFRAME_VERBATIM
+-----------+-------------------------------------------------------+ +=========+===============================================+
| Data | Description | | Data | Description |
+-----------+-------------------------------------------------------+ +=========+===============================================+
| "u(n\*i)" | Unencoded subblock, where "n" is frame's bits-per- | | u(n\*i) | Unencoded subblock, where "n" is frame's |
| | sample and "i" is frame's blocksize. | | | bits-per-sample and "i" is frame's blocksize. |
+-----------+-------------------------------------------------------+ +---------+-----------------------------------------------+
Table 34
11.27. RESIDUAL 11.27. RESIDUAL
+-------------------------------------------+-----------------------+ +==================================================+======================+
| Data | Description | |Data |Description |
+-------------------------------------------+-----------------------+ +==================================================+======================+
| "u(2)" | "RESIDUAL_CODING_METH | |u(2) |RESIDUAL_CODING_METHOD|
| | OD" | +--------------------------------------------------+----------------------+
| "RESIDUAL_CODING_METHOD_PARTITIONED_EXP_G | | |"RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB" ||| |
| OLOMB" || "RESIDUAL_CODING_METHOD_PARTITI | | |"RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2" | |
| ONED_EXP_GOLOMB2" | | +--------------------------------------------------+----------------------+
+-------------------------------------------+-----------------------+
Table 35
11.27.1. RESIDUAL_CODING_METHOD 11.27.1. RESIDUAL_CODING_METHOD
+--------+----------------------------------------------------------+
| Value | Description | +=======+========================================================+
+--------+----------------------------------------------------------+ | Value | Description |
| 0b00 | partitioned Exp-Golomb coding with 4-bit Exp-Golomb | +=======+========================================================+
| | parameter; RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB | | 0b00 | partitioned Exp-Golomb coding with 4-bit Exp-Golomb |
| | follows | | | parameter; |
| 0b01 | partitioned Exp-Golomb coding with 5-bit Exp-Golomb | | | RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB follows |
| | parameter; | +-------+--------------------------------------------------------+
| | RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2 follows | | 0b01 | partitioned Exp-Golomb coding with 5-bit Exp-Golomb |
| 0b10 - | reserved | | | parameter; |
| 0b11 | | | | RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2 follows |
+--------+----------------------------------------------------------+ +-------+--------------------------------------------------------+
| 0b10 | reserved |
| - | |
| 0b11 | |
+-------+--------------------------------------------------------+
Table 36
11.27.2. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB 11.27.2. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB
+-------------------------+-----------------------------------+ +=========================+===================================+
| Data | Description | | Data | Description |
+=========================+===================================+
| u(4) | Partition order. |
+-------------------------+-----------------------------------+ +-------------------------+-----------------------------------+
| "u(4)" | Partition order. |
| "EXP_GOLOMB_PARTITION"+ | There will be 2^order partitions. | | "EXP_GOLOMB_PARTITION"+ | There will be 2^order partitions. |
+-------------------------+-----------------------------------+ +-------------------------+-----------------------------------+
Table 37
11.27.2.1. EXP_GOLOMB_PARTITION 11.27.2.1. EXP_GOLOMB_PARTITION
+------------+------------------------------------------------------+ +==========+====================================================+
| Data | Description | | Data | Description |
+------------+------------------------------------------------------+ +==========+====================================================+
| "u(4(+5))" | "EXP-GOLOMB PARTITION ENCODING PARAMETER" (see | | u(4(+5)) | "EXP-GOLOMB PARTITION ENCODING PARAMETER" (see |
| | Section 11.27.2.2) | | | section on EXP-GOLOMB PARTITION ENCODING PARAMETER |
| "u(?)" | "ENCODED RESIDUAL" (see Section 11.27.4) | | | (#exp-golomb-partition-encoding-parameter)) |
+------------+------------------------------------------------------+ +----------+----------------------------------------------------+
| u(?) | "ENCODED RESIDUAL" (see section on ENCODED |
| | RESIDUAL (#encoded-residual)) |
+----------+----------------------------------------------------+
Table 38
11.27.2.2. EXP GOLOMB PARTITION ENCODING PARAMETER 11.27.2.2. EXP GOLOMB PARTITION ENCODING PARAMETER
+----------+--------------------------------------------------------+ +==========+==========================================+
| Value | Description | | Value | Description |
+----------+--------------------------------------------------------+ +==========+==========================================+
| 0b0000 - | Exp-golomb parameter. | | 0b0000 - | Exp-golomb parameter. |
| 0b1110 | | | 0b1110 | |
| 0b1111 | Escape code, meaning the partition is in unencoded | +----------+------------------------------------------+
| | binary form using n bits per sample; n follows as a | | 0b1111 | Escape code, meaning the partition is in |
| | 5-bit number. | | | unencoded binary form using n bits per |
+----------+--------------------------------------------------------+ | | sample; n follows as a 5-bit number. |
+----------+------------------------------------------+
Table 39
11.27.3. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2 11.27.3. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2
+--------------------------+-----------------------------------+ +==========================+===================================+
| Data | Description | | Data | Description |
+==========================+===================================+
| u(4) | Partition order. |
+--------------------------+-----------------------------------+ +--------------------------+-----------------------------------+
| "u(4)" | Partition order. |
| "EXP-GOLOMB2_PARTITION"+ | There will be 2^order partitions. | | "EXP-GOLOMB2_PARTITION"+ | There will be 2^order partitions. |
+--------------------------+-----------------------------------+ +--------------------------+-----------------------------------+
Table 40
11.27.3.1. EXP_GOLOMB2_PARTITION 11.27.3.1. EXP_GOLOMB2_PARTITION
+------------+------------------------------------------------------+ +==========+=====================================================+
| Data | Description | | Data | Description |
+------------+------------------------------------------------------+ +==========+=====================================================+
| "u(5(+5))" | "EXP-GOLOMB2 PARTITION ENCODING PARAMETER" (see | | u(5(+5)) | "EXP-GOLOMB2 PARTITION ENCODING PARAMETER" (see |
| | Section 11.27.3.2) | | | section on EXP-GOLOMB2 PARTITION ENCODING PARAMETER |
| "u(?)" | "ENCODED RESIDUAL" (see Section 11.27.4) | | | (#expgolomb2-partition-encoding-parameter)) |
+------------+------------------------------------------------------+ +----------+-----------------------------------------------------+
| u(?) | "ENCODED RESIDUAL" (see section on ENCODED RESIDUAL |
| | (#encoded-residual)) |
+----------+-----------------------------------------------------+
Table 41
11.27.3.2. EXP-GOLOMB2 PARTITION ENCODING PARAMETER 11.27.3.2. EXP-GOLOMB2 PARTITION ENCODING PARAMETER
+----------+--------------------------------------------------------+ +===========+==========================================+
| Value | Description | | Value | Description |
+----------+--------------------------------------------------------+ +===========+==========================================+
| 0b00000 | Exp-golomb parameter. | | 0b00000 - | Exp-golomb parameter. |
| - | | | 0b11110 | |
| 0b11110 | | +-----------+------------------------------------------+
| 0b11111 | Escape code, meaning the partition is in unencoded | | 0b11111 | Escape code, meaning the partition is in |
| | binary form using n bits per sample; n follows as a | | | unencoded binary form using n bits per |
| | 5-bit number. | | | sample; n follows as a 5-bit number. |
+----------+--------------------------------------------------------+ +-----------+------------------------------------------+
Table 42
11.27.4. ENCODED RESIDUAL 11.27.4. ENCODED RESIDUAL
The number of samples (n) in the partition is determined as follows: The number of samples (n) in the partition is determined as follows:
o if the partition order is zero, n = frame's blocksize - predictor * if the partition order is zero, n = frame's blocksize - predictor
order order
o else if this is not the first partition of the subframe, n = * else if this is not the first partition of the subframe, n =
(frame's blocksize / (2^partition order)) (frame's blocksize / (2^partition order))
o else n = (frame's blocksize / (2^partition order)) - predictor * else n = (frame's blocksize / (2^partition order)) - predictor
order order
12. References 12. Normative References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
12.2. URIs [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
[1] https://xiph.org/flac/ogg_mapping.html May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[2] https://xiph.org/flac/documentation_format_overview.html
[3] http://svr-www.eng.cam.ac.uk/~ajr/
[4] http://svr-www.eng.cam.ac.uk/reports/abstracts/
robinson_tr156.html
[5] https://web.archive.org/web/20040215005354/http://csi.usc.edu/
faculty/golomb.html
[6] http://en.wikipedia.org/wiki/Claude_Shannon
[7] https://en.wikipedia.org/wiki/Linear_predictive_coding
[8] http://www.hpl.hp.com/techreports/1999/HPL-1999-144.pdf
[9] http://svr-www.eng.cam.ac.uk/reports/abstracts/
robinson_tr156.html
[10] http://www.hpl.hp.com/techreports/1999/HPL-1999-144.pdf
[11] http://svr-www.eng.cam.ac.uk/reports/abstracts/
robinson_tr156.html
[12] https://en.wikipedia.org/wiki/Exponential-Golomb_coding
[13] http://www.hpl.hp.com/techreports/98/HPL-98-193.html
[14] http://web.archive.org/web/20140827133312/http://www.cs.tut.fi/~
albert/Dev/pucrunch/packing.html
[15] https://xiph.org/flac/id.html
[16] http://xiph.org/vorbis/doc/v-comment.html
[17] http://www.id3.org/id3v2.4.0-frames
[18] https://xiph.org/flac/id.html
[19] http://www.xiph.org/vorbis/doc/v-comment.html
[20] http://isrc.ifpi.org/
[21] http://www.disctronics.co.uk/technology/cdaudio/cdaud_isrc.htm
[22] http://www.chipchapin.com/CDMedia/cdda9.php3
[23] http://lists.xiph.org/pipermail/flac-
dev/2008-December/002607.html
Authors' Addresses Authors' Addresses
Josh Coalson Michael Sandelman
Xiph.Org Foundation Email: mcr@sandelman.ca
Andrew Weaver Andrew Weaver
Email: theandrewjw@gmail.com Email: theandrewjw@gmail.com
 End of changes. 186 change blocks. 
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