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<div class="box_body">
This is a detailed description of the FLAC format. There is also a companion document that describes <a href="ogg_mapping.html">FLAC-to-Ogg mapping</a>.<br />
<br />
+ For a user-oriented overview, see <a href="documentation_format_overview.html">About the FLAC Format</a>.<br />
+ <br />
<a name="toc"><font size="+1"><b><u>Table of Contents</u></b></font></a>
<ul>
<li><a href="#acknowledgments">Acknowledgments</a></li>
</li>
</ul>
</li>
+ <li><a href="#metadata_block_picture">METADATA_BLOCK_PICTURE</a></li>
</ul>
</li>
</ul>
<li><a href="#rice_partition">RICE_PARTITION</a></li>
</ul>
</li>
+ <li><a href="#partitioned_rice2">RESIDUAL_CODING_METHOD_PARTITIONED_RICE2</a>
+ <ul>
+ <li><a href="#rice2_partition">RICE2_PARTITION</a></li>
+ </ul>
+ </li>
</ul>
</li>
</ul>
</ul>
</li>
</ul>
- <a name="acknowledgments"><font size="+1"><b><u>Acknowledgments</u></b></font></a>
- <br /><br />
+ <a name="acknowledgments"><font size="+1"><b><u>Acknowledgments</u></b></font></a><br />
+ <br />
FLAC owes much to the many people who have advanced the audio compression field so freely. For instance:
<ul>
<li>
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.
</li>
<li>
- And of course, <a href="http://www.digitalcentury.com/encyclo/update/shannon.html">Claude Shannon</a>
+ And of course, <a href="http://en.wikipedia.org/wiki/Claude_Shannon">Claude Shannon</a>
</li>
</ul>
- <a name="scope"><font size="+1"><b><u>Scope</u></b></font></a>
- <br /><br />
- It is a known fact that no algorithm can losslessly compress all possible input, so most compressors restrict themselves to a useful domain and try to work as well as possible within that domain. FLAC's domain is audio data. Though it can losslessly <b>code</b> any input, only certain kinds of input will get smaller. FLAC exploits the fact that audio data typically has a high degree of sample-to-sample correlation.
- <br /><br />
- Within the audio domain, there are many possible subdomains. For example: low bitrate speech, high-bitrate multi-channel music, etc. FLAC itself does not target a specific subdomain but many of the default parameters of the reference encoder are tuned to CD-quality music data (i.e. 44.1kHz, 2 channel, 16 bits per sample). The effect of the encoding parameters on different kinds of audio data will be examined later.
- <br /><br />
- <a name="architecture"><font size="+1"><b><u>Architecture</u></b></font></a>
- <br /><br />
+ <a name="scope"><font size="+1"><b><u>Scope</u></b></font></a><br />
+ <br />
+ It is a known fact that no algorithm can losslessly compress all possible input, so most compressors restrict themselves to a useful domain and try to work as well as possible within that domain. FLAC's domain is audio data. Though it can losslessly <b>code</b> any input, only certain kinds of input will get smaller. FLAC exploits the fact that audio data typically has a high degree of sample-to-sample correlation.<br />
+ <br />
+ Within the audio domain, there are many possible subdomains. For example: low bitrate speech, high-bitrate multi-channel music, etc. FLAC itself does not target a specific subdomain but many of the default parameters of the reference encoder are tuned to CD-quality music data (i.e. 44.1kHz, 2 channel, 16 bits per sample). The effect of the encoding parameters on different kinds of audio data will be examined later.<br />
+ <br />
+ <a name="architecture"><font size="+1"><b><u>Architecture</u></b></font></a><br />
+ <br />
Similar to many audio coders, a FLAC encoder has the following stages:
<ul>
<li>
<a href="#residualcoding">Residual coding</a>. If the predictor does not describe the signal exactly, the difference between the original signal and the predicted signal (called the error or residual signal) must be coded losslessy. If the predictor is effective, the residual signal will require fewer bits per sample than the original signal. FLAC currently uses only one method for encoding the residual (see the <a href="#residualcoding">Residual coding</a> section), but the format has reserved space for additional methods. FLAC allows the residual coding method to change from block to block, or even within the channels of a block.
</li>
</ul>
- In addition, FLAC specifies a metadata system, which allows arbitrary information about the stream to be included at the beginning of the stream.
- <br /><br />
- <a name="definitions"><font size="+1"><b><u>Definitions</u></b></font></a>
- <br /><br />
- Many terms like "block" and "frame" are used to mean different things in differenct encoding schemes. For example, a frame in MP3 corresponds to many samples across several channels, whereas an S/PDIF frame represents just one sample for each channel. The definitions we use for FLAC follow. Note that when we talk about blocks and subblocks we are refering to the raw unencoded audio data that is the input to the encoder, and when we talk about frames and subframes, we are refering to the FLAC-encoded data.
+ In addition, FLAC specifies a metadata system, which allows arbitrary information about the stream to be included at the beginning of the stream.<br />
+ <br />
+ <a name="definitions"><font size="+1"><b><u>Definitions</u></b></font></a><br />
+ <br />
+ Many terms like "block" and "frame" are used to mean different things in differenct encoding schemes. For example, a frame in MP3 corresponds to many samples across several channels, whereas an S/PDIF frame represents just one sample for each channel. The definitions we use for FLAC follow. Note that when we talk about 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 subframes, we are referring to the FLAC-encoded data.
<ul>
<li>
<b>Block</b>: One or more audio samples that span several channels.
<b>Subframe</b>: A subframe header plus one or more encoded samples from a given channel. All subframes within a frame will contain the same number of samples.
</li>
</ul>
- <a name="blocking"><font size="+1"><b><u>Blocking</u></b></font></a>
- <br /><br />
- 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 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 signal may vary so much that the encoder will be unable to find a good predictor. In order to simplify encoder/decoder design, FLAC imposes a minimum block size of 16 samples, and a maximum block size of 65535 samples. This range covers the optimal size for all of the audio data FLAC supports.
- <br /><br />
- Currently the reference encoder uses a fixed block size, optimized on the sample rate of the input. Future versions may vary the block size depending on the characteristics of the signal.
- <br /><br />
- Blocked data is passed to the predictor stage one subblock (channel) at a time. Each subblock is independently coded into a subframe, and the subframes are concatenated into a frame. Because each channel is coded separately, it means that one channel of a stereo frame may be encoded as a constant subframe, and the other an LPC subframe.
- <br /><br />
- <a name="interchannel"><font size="+1"><b><u>Interchannel Decorrelation</u></b></font></a>
- <br /><br />
- In stereo streams, in many cases there is an exploitable amount of correlation between the left and right channels. FLAC allows the frames of stereo streams to have different channel assignments, and an encoder may choose to use the best representation on a frame-by-frame basis.
+ <a name="blocking"><font size="+1"><b><u>Blocking</u></b></font></a><br />
+ <br />
+ 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 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 signal may vary so much that the encoder will be unable to find a good predictor. In order to simplify encoder/decoder design, FLAC imposes a minimum block size of 16 samples, and a maximum block size of 65535 samples. This range covers the optimal size for all of the audio data FLAC supports.<br />
+ <br />
+ Currently the reference encoder uses a fixed block size, optimized on the sample rate of the input. Future versions may vary the block size depending on the characteristics of the signal.<br />
+ <br />
+ Blocked data is passed to the predictor stage one subblock (channel) at a time. Each subblock is independently coded into a subframe, and the subframes are concatenated into a frame. Because each channel is coded separately, it means that one channel of a stereo frame may be encoded as a constant subframe, and the other an LPC subframe.<br />
+ <br />
+ <a name="interchannel"><font size="+1"><b><u>Interchannel Decorrelation</u></b></font></a><br />
+ <br />
+ In stereo streams, many times there is an exploitable amount of correlation between the left and right channels. FLAC allows the frames of stereo streams to have different channel assignments, and an encoder may choose to use the best representation on a frame-by-frame basis.
<ul>
<li>
<b>Independent</b>. The left and right channels are coded independently.
<b>Right-side</b>. The right channel and side channel are coded
</li>
</ul>
- Surprisingly, the left-side and right-side forms can be the most efficient in many frames, even though the raw number of bits per sample needed for the original signal is slightly more than that needed for independent or mid-side coding.
- <br /><br />
- <a name="prediction"><font size="+1"><b><u>Prediction</u></b></font></a>
- <br /><br />
+ Surprisingly, the left-side and right-side forms can be the most efficient in many frames, even though the raw number of bits per sample needed for the original signal is slightly more than that needed for independent or mid-side coding.<br />
+ <br />
+ <a name="prediction"><font size="+1"><b><u>Prediction</u></b></font></a><br />
+ <br />
FLAC uses four methods for modeling the input signal:
<ul>
<li>
<b>Fixed linear predictor</b>. FLAC uses a class of computationally-efficient fixed linear predictors (for a good description, see <a href="http://www.hpl.hp.com/techreports/1999/HPL-1999-144.pdf">audiopak</a> and <a href="http://svr-www.eng.cam.ac.uk/~ajr/GroupPubs/Robinson94-tr156/index.html">shorten</a>). FLAC adds a fourth-order predictor to the zero-to-third-order 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.
</li>
<li>
- <b>FIR Linear prediction</b>. For more accurate modeling (at a cost of slower encoding), FLAC supports up to 32nd order FIR linear prediction (again, for info on linear prediction, see <a href="http://www.hpl.hp.com/techreports/1999/HPL-1999-144.pdf">audiopak</a> and <a href="http://svr-www.eng.cam.ac.uk/~ajr/GroupPubs/Robinson94-tr156/index.html">shorten</a>). The reference encoder uses the Levinson-Durbin method for calculating the LPC coefficients from the autocorrelation coefficients, and the coefficients are quantized before computing the residual. Whereas encoders such as Shorten used a fixed quantization for the entire input, FLAC allows the quantized coefficient precision 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.
+ <b>FIR Linear prediction</b>. For more accurate modeling (at a cost of slower encoding), FLAC supports up to 32nd order FIR linear prediction (again, for info
rmation on linear prediction, see <a href="http://www.hpl.hp.com/techreports/1999/HPL-1999-144.pdf">audiopak</a> and <a href="http://svr-www.eng.cam.ac.uk/~ajr/GroupPubs/Robinson94-tr156/index.html">shorten</a>). The reference encoder uses the Levinson-Durbin method for calculating the LPC coefficients from the autocorrelation coefficients, and the coefficients are quantized before computing the residual. Whereas encoders such as Shorten used a fixed quantization for the entire input, FLAC allows the quantized coefficient precision 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.
</li>
</ul>
- <a name="residualcoding"><font size="+1"><b><u>Residual Coding</u></b></font></a>
- <br /><br />
- FLAC currently defines two similar methods for the coding of the error signal from the prediction stage. The error signal is coded using Rice codes in one of two ways: 1) the encoder estimates a single rice parameter based on the variance of the residual and Rice codes the entire residual using this parameter; 2) the residual is partitioned into several equal-length regions of contiguous samples, and each region is coded with its own Rice parameter based on the region's mean. (Note that the first method is a special case of the second method with one partition, except the Rice parameter is based on the residual variance instead of the mean.)
- <br /><br />
- The FLAC format has reserved space for other coding methods. Some possiblities for volunteers would be to explore better context-modeling of the Rice parameter, or Huffman coding. See <a href="http://www.hpl.hp.com/techreports/98/HPL-98-193.html">LOCO-I</a> and <a href="http://www.cs.tut.fi/~albert/Dev/pucrunch/packing.html">pucrunch</a> for descriptions of several universal codes.
- <br /><br />
- <a name="format_overview"><font size="+1"><b><u>Format</u></b></font></a>
- <br /><br />
- This section specifies the FLAC bitstream format. FLAC has no format version information, but it does contain reserved space in several places. Future versions of the format may use this reserved space safely without breaking the format of older streams. Older decoders may choose to abort decoding or skip data encoded with newer methods. Apart from reserved patterns, in places the format specifies invalid patterns, meaning that the patterns may never appear in any valid bitstream, in any prior, present, or future versions of the format. These invalid patterns are usually used to make the synchronization mechanism more robust.
- <br /><br />
- All numbers used in a FLAC bitstream are integers; there are no floating-point representations. All numbers are big-endian coded. All numbers are unsigned unless otherwise specified.
- <br /><br />
+ <a name="residualcoding"><font size="+1"><b><u>Residual Coding</u></b></font></a><br />
+ <br />
+ FLAC currently defines two similar methods for the coding of the error signal from the prediction stage. The error signal is coded using Rice codes in one of two ways: 1) the encoder estimates a single Rice parameter based on the variance of the residual and Rice codes the entire residual using this parameter; 2) the residual is partitioned into several equal-length regions of contiguous samples, and each region is coded with its own Rice parameter based on the region's mean. (Note that the first method is a special case of the second method with one partition, except the Rice parameter is based on the residual variance instead of the mean.)<br />
+ <br />
+ The FLAC format has reserved space for other coding methods. Some possiblities for volunteers would be to explore better context-modeling of the Rice parameter, or Huffman coding. See <a href="http://www.hpl.hp.com/techreports/98/HPL-98-193.html">LOCO-I</a> and <a href="http://www.cs.tut.fi/~albert/Dev/pucrunch/packing.html">pucrunch</a> for descriptions of several universal codes.<br />
+ <br />
+ <a name="format_overview"><font size="+1"><b><u>Format</u></b></font></a><br />
+ <br />
+ This section specifies the FLAC bitstream format. FLAC has no format version information, but it does contain reserved space in several places. Future versions of the format may use this reserved space safely without breaking the format of older streams. Older decoders may choose to abort decoding or skip data encoded with newer methods. Apart from reserved patterns, in places the format specifies invalid patterns, meaning that the patterns may never appear in any valid bitstream, in any prior, present, or future versions of the format. These invalid patterns are usually used to make the synchronization mechanism more robust.<br />
+ <br />
+ All numbers used in a FLAC bitstream are integers; there are no floating-point representations. All numbers are big-endian coded. All numbers are unsigned unless otherwise specified.<br />
+ <br />
Before the formal description of the stream, an overview might be helpful.
<ul>
<li>
<li>
FLAC supports up to 128 kinds of metadata blocks; currently the following are defined:
<ul>
- <li><a name="def_STREAMINFO" /><b>STREAMINFO</b>: This block has information about the whole stream, like sample rate, number of channels, total number of samples, etc. It must be present as the first metadata block in the stream. Other metadata blocks may follow, and ones that the decoder doesn't understand, it will skip.</li>
- <li><a name="def_APPLICATION" /><b>APPLICATION</b>: This block is for use by third-party applications. The only mandatory field is a 32-bit identifier. This ID is granted upon request to an application by the FLAC maintainers. The remainder is of the block is defined by the registered application. Visit the <a href="id.html">registration page</a> if you would like to register an ID for your application with FLAC.</li>
- <li><a name="def_PADDING" /><b>PADDING</b>: This block allows for an arbitrary amount of padding. The contents of a PADDING block have no meaning. This block is useful when it is known that metadata will be edited after encoding; the user can instruct the encoder to reserve a PADDING block of sufficient size so that when metadata is added, it will simply overwrite the padding (which is relatively quick) instead of having to insert it into the right place in the existing file (which would normally require rewriting the entire file).</li>
- <li><a name="def_SEEKTABLE" /><b>SEEKTABLE</b>: This is an optional block for storing seek points. It is possible to seek to any given sample in a FLAC stream without a seek table, but the delay can be unpredictable since the bitrate may vary widely within a stream. By adding seek points to a stream, this delay can be significantly reduced. 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, but the table can have any number of seek points. There is also a special 'placeholder' seekpoint which will be ignored by decoders but which can be used to reserve space for future seek point insertion.</li>
- <li><a name="def_VORBIS_COMMENT" /><b>VORBIS_COMMENT</b>: This block is for storing a list of human-readable name/value pairs. Values are encoded using UTF-8. It is an implementation of the <a href="http://xiph.org/ogg/vorbis/doc/v-comment.html">Vorbis comment specification</a>. This is the only officially supported tagging mechanism in FLAC. There may be only one VORBIS_COMMENT block in a stream. In some external documentation, Vorbis comments are called FLAC tags to lessen confusion.</li>
- <li><a name="def_CUESHEET" /><b>CUESHEET</b>: This block is for storing various information that can be used in a cue sheet. It supports track and index points, compatible with Red Book CD digital audio discs, as well as other CD-DA metadata such as media catalog number and track ISRCs. The CUESHEET block is especially useful for backing up CD-DA discs, but it can be used as a general purpose cueing mechanism for playback.</li>
+ <li><a name="def_STREAMINFO"><b>STREAMINFO</b></a>: This block has information about the whole stream, like sample rate, number of channels, total number of samples, etc. It must be present as the first metadata block in the stream. Other metadata blocks may follow, and ones that the decoder doesn't understand, it will skip.</li>
+ <li><a name="def_APPLICATION"><b>APPLICATION</b></a>: This block is for use by third-party applications. The only mandatory field is a 32-bit identifier. This ID is granted upon request to an application by the FLAC maintainers. The remainder is of the block is defined by the registered application. Visit the <a href="id.html">registration page</a> if you would like to register an ID for your application with FLAC.</li>
+ <li><a name="def_PADDING"><b>PADDING</b></a>: This block allows for an arbitrary amount of padding. The contents of a PADDING block have no meaning. This block is useful when it is known that metadata will be edited after encoding; the user can instruct the encoder to reserve a PADDING block of sufficient size so that when metadata is added, it will simply overwrite the padding (which is relatively quick) instead of having to insert it into the right place in the existing file (which would normally require rewriting the entire file).</li>
+ <li><a name="def_SEEKTABLE"><b>SEEKTABLE</b></a>: This is an optional block for storing seek points. It is possible to seek to any given sample in a FLAC stream without a seek table, but the delay can be unpredictable since the bitrate may vary widely within a stream. By adding seek points to a stream, this delay can be significantly reduced. 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, but the table can have any number of seek points. There is also a special 'placeholder' seekpoint which will be ignored by decoders but which can be used to reserve space for future seek point insertion.</li>
+ <li><a name="def_VORBIS_COMMENT"><b>VORBIS_COMMENT</b></a>: This block is for storing a list of human-readable name/value pairs. Values are encoded using UTF-8. It is an implementation of the <a href="http://xiph.org/vorbis/doc/v-comment.html">Vorbis comment specification</a> (without the framing bit). This is the only officially supported tagging mechanism in FLAC. There may be only one VORBIS_COMMENT block in a stream. In some external documentation, Vorbis comments are called FLAC tags to lessen confusion.</li>
+ <li><a name="def_CUESHEET"><b>CUESHEET</b></a>: This block is for storing various information that can be used in a cue sheet. It supports track and index points, compatible with Red Book CD digital audio discs, as well as other CD-DA metadata such as media catalog number and track ISRCs. The CUESHEET block is especially useful for backing up CD-DA discs, but it can be used as a general purpose cueing mechanism for playback.</li>
+ <li><a name="def_PICTURE"><b>PICTURE</b></a>: This block is for storing pictures associated with the file, most commonly cover art from CDs. There may be more than one PICTURE block in a file. The picture format is similar to the <a href="http://www.id3.org/id3v2.4.0-frames.txt">APIC frame in ID3v2</a>. The PICTURE block has a type, MIME type, and UTF-8 description like ID3v2, and supports external linking via URL (though this is discouraged). The differences are that there is no uniqueness constraint on the description field, and the MIME type is mandatory. The FLAC PICTURE block also includes the resolution, color depth, and palette size so that the client can search for a suitable picture without having to scan them all.</li>
</ul>
</li>
<li>
- The audio data is composed of one or more audio frames. Each frame consists of a frame header, which contains a sync code, info about the frame like the block size, sample rate, 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 frame (for variable-blocksize streams), or the frame number (for fixed-blocksize streams). This allows for fast, sample-accurate seeking to be performed. Following the frame header are encoded subframes, one for each channel, and finally, the frame is zero-padded to a byte boundary. Each subframe has its own header that specifies how the subframe is encoded.
+ The audio data is composed of one or more audio frames. Each frame consists of a frame header, which contains a sync code, information about the frame like the block size, sample rate, 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 frame (for variable-blocksize streams), or the frame number (for fixed-blocksize streams). This allows for fast, sample-accurate seeking to be performed. Following the frame header are encoded subframes, one for each channel, and finally, the frame is zero-padded to a byte boundary. Each subframe has its own header that specifies how the subframe is encoded.
</li>
<li>
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 14-bit sync code begins each frame. The sync code will not appear anywhere else in the frame header. However, since it may appear 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 header contains no invalid data. Even this is not foolproof since valid header patterns can still occur within the subframes. The 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.
Individual subframes (one for each channel) are coded separately within a frame, and appear serially in the stream. In other words, the encoded audio data is NOT channel-interleaved. This reduces decoder complexity at the cost of requiring larger decode buffers. Each subframe has its own header specifying the attributes of the subframe, like prediction method and order, residual coding parameters, etc. The header is followed by the encoded audio data for that channel.
</li>
<li>
- <a name="subset" />FLAC specifies a subset of itself as the Subset format. The purpose of this is to ensure that any streams encoded according to the Subset are truly "streamable", meaning that a decoder that cannot seek within the stream can still pick up in the middle of the stream and start decoding. It also makes hardware decoder implementations more practical by limiting the encoding parameters such that decoder buffer sizes and other resource requirements can be easily determined. "flac" generates Subset streams by default unless the "--lax" command-line option is used. The Subset makes the following limitations on what may be used in the stream:
+ <a name="subset">FLAC</a> specifies a subset of itself as the Subset format. The purpose of this is to ensure that any streams encoded according to the Subset are truly "streamable", meaning that a decoder that cannot seek within the stream can still pick up in the middle of the stream and start decoding. It also makes hardware decoder implementations more practical by limiting the encoding parameters such that decoder buffer sizes and other resource requirements can be easily determined. <span class="commandname">flac</span> generates Subset streams by default unless the "--lax" command-line option is used. The Subset makes the following limitations on what may be used in the stream:
<ul>
<li>
- The blocksize bits in the <a href="#frame_header">frame header</a> must be 0001-0101 or 1000-1110, specifying a fixed-blocksize stream (the exception being the last block as described in the table) and a few allowable blocksizes. This also means that the STREAMINFO metadata block must specify equal mininum and maximum blocksizes.
+ The blocksize bits in the <a href="#frame_header">frame header</a> must be 0001-1110. The blocksize must be <=16384; if the sample rate is <= 48000Hz, the blocksize must be <=4608.
</li>
<li>
- The sample rate bits in the <a href="#frame_header">frame header</a> must be 0001-1011.
+ The sample rate bits in the <a href="#frame_header">frame header</a> must be 0001-1110.
</li>
<li>
The bits-per-sample bits in the <a href="#frame_header">frame header</a> must be 001-111.
</li>
<li>
+ If the sample rate is <= 48000Hz, the filter order in <a href="#subframe_lpc">LPC subframes</a> must be less than or equal to 12, i.e. the subframe type bits in the <a href="#subframe_header">subframe header</a> may not be 101100-111111.
+ </li>
+ <li>
The Rice partition order in a <a href="#partitioned_rice">Rice-coded residual section</a> must be less than or equal to 8.
</li>
</ul>
<tt>5</tt> : CUESHEET
</li>
<li>
- <tt>6-126</tt> : reserved
+ <tt>6</tt> : PICTURE
+ </li>
+ <li>
+ <tt>7-126</tt> : reserved
</li>
<li>
<tt>127</tt> : invalid, to avoid confusion with a frame sync code
|| <a href="#metadata_block_application"><i>METADATA_BLOCK_APPLICATION</i></a><br />
|| <a href="#metadata_block_seektable"><i>METADATA_BLOCK_SEEKTABLE</i></a><br />
|| <a href="#metadata_block_vorbis_comment"><i>METADATA_BLOCK_VORBIS_COMMENT</i></a><br />
- || <a href="#metadata_block_cuesheet"><i>METADATA_BLOCK_CUESHEET</i></a>
+ || <a href="#metadata_block_cuesheet"><i>METADATA_BLOCK_CUESHEET</i></a><br />
+ || <a href="#metadata_block_picture"><i>METADATA_BLOCK_PICTURE</i></a>
</td>
<td>
The block data must match the block type in the block header.
<20>
</td>
<td>
- Sample rate in Hz. Though 20 bits are available, the maximum sample rate is limited by the structure of frame headers to 1048570Hz. Also, a value of 0 is invalid.
+ Sample rate in Hz. Though 20 bits are available, the maximum sample rate is limited by the structure of frame headers to 655350Hz. Also, a value of 0 is invalid.
</td>
</tr>
<tr>
<n>
</td>
<td>
- Also known as FLAC tags, the contents of a vorbis comment packet as specified <a href="http://www.xiph.org/ogg/vorbis/doc/v-comment.html">here</a>, including the vendor string. Note that the vorbis comment spec allows for on the order of 2 ^ 64 bytes of data where as the FLAC metadata block is limited to 2 ^ 24 bytes. Given the stated purpose of vorbis comments, i.e. human-readable textual information, this limit is unlikely to be restrictive. Also note that the 32-bit field lengths are little-endian coded according to the vorbis spec, as opposed to the usual big-endian coding of fixed-length integers in the rest of FLAC.
+ Also known as FLAC tags, the contents of a vorbis comment packet as specified <a href="http://www.xiph.org/vorbis/doc/v-comment.html">here</a> (without the framing bit). Note that the vorbis comment spec allows for on the order of 2 ^ 64 bytes of data where as the FLAC metadata block is limited to 2 ^ 24 bytes. Given the stated purpose of vorbis comments, i.e. human-readable textual information, this limit is unlikely to be restrictive. Also note that the 32-bit field lengths are little-endian coded according to the vorbis spec, as opposed to the usual big-endian coding of fixed-length integers in the rest of FLAC.
</td>
</tr>
</table>
<8>
</td>
<td>
- The number of tracks. For CD-DA, this number must be no more than 100 (99 regular tracks and one leadout track).
+ The number of tracks. Must be at least 1 (because of the requisite lead-out track). For CD-DA, this number must be no more than 100 (99 regular tracks and one lead-out track).
</td>
</tr>
<tr>
<a href="#cuesheet_track"><i>CUESHEET_TRACK</i></a>+
</td>
<td>
- 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.
+ 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 is must be 255.
</td>
</tr>
</table>
<8>
</td>
<td>
- Track number. A track number of 0 is not allowed to avoid conflicting with the CD-DA spec, which reserves this for the lead-in. For CD-DA the number must be 1-99, or 170 for the lead-out. It is not required but encouraged to start with track 1 and increase sequentially. Track numbers must be unique within a CUESHEET.
+ Track number. A track number of 0 is not allowed to avoid conflicting with the CD-DA spec, which reserves this for the lead-in. For CD-DA the number must be 1-99, or 170 for the lead-out; for non-CD-DA, the track number must for 255 for the lead-out. It is not required but encouraged to start with track 1 and increase sequentially. Track numbers must be unique within a CUESHEET.
</td>
</tr>
<tr>
<div class="box">
<table width="100%" border="0" cellspacing="0" cellpadding="0" bgcolor="#EEEED4"><tr><td>
+ <table width="100%" border="1">
+ <tr>
+ <td colspan="2" bgcolor="#D3D4C5">
+ <a name="metadata_block_picture"><font size="+1"><b>METADATA_BLOCK_PICTURE</b></font></a>
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ The picture type according to the ID3v2 APIC frame:<br />
+ <ul>
+ <li>0 - Other</li>
+ <li>1 - 32x32 pixels 'file icon' (PNG only)</li>
+ <li>2 - Other file icon</li>
+ <li>3 - Cover (front)</li>
+ <li>4 - Cover (back)</li>
+ <li>5 - Leaflet page</li>
+ <li>6 - Media (e.g. label side of CD)</li>
+ <li>7 - Lead artist/lead performer/soloist</li>
+ <li>8 - Artist/performer</li>
+ <li>9 - Conductor</li>
+ <li>10 - Band/Orchestra</li>
+ <li>11 - Composer</li>
+ <li>12 - Lyricist/text writer</li>
+ <li>13 - Recording Location</li>
+ <li>14 - During recording</li>
+ <li>15 - During performance</li>
+ <li>16 - Movie/video screen capture</li>
+ <li>17 - A bright coloured fish</li>
+ <li>18 - Illustration</li>
+ <li>19 - Band/artist logotype</li>
+ <li>20 - Publisher/Studio logotype</li>
+ </ul>
+ Others are reserved and should not be used. There may only be one each of picture type 1 and 2 in a file.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ The length of the MIME type string in bytes.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <n*8>
+ </td>
+ <td>
+ The MIME type string, in printable ASCII characters 0x20-0x7e. The MIME type may also be <tt>--></tt> to signify that the data part is a URL of the picture instead of the picture data itself.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ The length of the description string in bytes.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <n*8>
+ </td>
+ <td>
+ The description of the picture, in UTF-8.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ The width of the picture in pixels.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ The height of the picture in pixels.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ The color depth of the picture in bits-per-pixel.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ For indexed-color pictures (e.g. GIF), the number of colors used, or <tt>0</tt> for non-indexed pictures.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <32>
+ </td>
+ <td>
+ The length of the picture data in bytes.
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <n*8>
+ </td>
+ <td>
+ The binary picture data.
+ </td>
+ </tr>
+ </table>
+ </td></tr></table>
+</div>
+
+<br />
+
+<div class="box">
+ <table width="100%" border="0" cellspacing="0" cellpadding="0" bgcolor="#EEEED4"><tr><td>
<table width="100%" border="1" bgcolor="#EEEED4">
<tr>
<td colspan="2" bgcolor="#D3D4C5">
</tr>
<tr>
<td align="right" valign="top" bgcolor="#F4F4CC">
- <2>
+ <1>
</td>
<td>
- Reserved:<br />
+ Reserved: <a href="#frame_header_notes">[1]</a><br />
+ <ul>
+ <li>
+ <tt>0</tt> : mandatory value
+ </li>
+ <li>
+ <tt>1</tt> : reserved for future use
+ </li>
+ </ul>
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <1>
+ </td>
+ <td>
+ Blocking strategy: <a href="#frame_header_notes">[2]</a> <a href="#frame_header_notes">[3]</a><br />
<ul>
<li>
- <tt>00</tt> : mandatory value
+ <tt>0</tt> : fixed-blocksize stream; frame header encodes the frame number
</li>
<li>
- <tt>01-11</tt> : reserved for future use
+ <tt>1</tt> : variable-blocksize stream; frame header encodes the sample number
</li>
</ul>
</td>
Block size in inter-channel samples:<br />
<ul>
<li>
- <tt>0000</tt> : get from STREAMINFO metadata block
+ <tt>0000</tt> : reserved
</li>
<li>
<tt>0001</tt> : 192 samples
<tt>0000</tt> : get from STREAMINFO metadata block
</li>
<li>
- <tt>0001-0011</tt> : reserved
+ <tt>0001</tt> : 88.2kHz
+ </li>
+ <li>
+ <tt>0010</tt> : 176.4kHz
+ </li>
+ <li>
+ <tt>0011</tt> : 192kHz
</li>
<li>
<tt>0100</tt> : 8kHz
Channel assignment
<ul>
<li>
- <tt>0000-0111</tt> : (number of independent channels)-1. when == 0001, channel 0 is the left channel and channel 1 is the right
+ <tt>0000-0111</tt> : (number of independent channels)-1. Where defined, the channel order follows SMPTE/ITU-R recommendations. The assignments are as follows:
+ <ul>
+ <li>1 channel: mono</li>
+ <li>2 channels: left, right</li>
+ <li>3 channels: left, right, center</li>
+ <li>4 channels: left, right, back left, back right</li>
+ <li>5 channels: left, right, center, back/surround left, back/surround right</li>
+ <li>6 channels: left, right, center, LFE, back/surround left, back/surround right</li>
+ <li>7 channels: not defined</li>
+ <li>8 channels: not defined</li>
+ </ul>
</li>
<li>
<tt>1000</tt> : left/side stereo: channel 0 is the left channel, channel 1 is the side(difference) channel
<1>
</td>
<td>
- Zero bit padding, to prevent sync-fooling string of 1s
+ Reserved:<br />
+ <ul>
+ <li>
+ <tt>0</tt> : mandatory value
+ </li>
+ <li>
+ <tt>1</tt> : reserved for future use
+ </li>
+ </ul>
</td>
</tr>
<tr>
</td>
<td>
if(variable blocksize)<br />
- <8-56>:"UTF-8" coded sample number (decoded number is 36 bits)<br />
+ <8-56>:"UTF-8" coded sample number (decoded number is 36 bits) <a href="#frame_header_notes">[4]</a><br />
else<br />
- <8-48>:"UTF-8" coded frame number (decoded number is 31 bits)
+ <8-48>:"UTF-8" coded frame number (decoded number is 31 bits) <a href="#frame_header_notes">[4]</a>
</td>
</tr>
<tr>
<td>
</td>
<td bgcolor="#F4F4CC">
- <font size="+1">NOTES</font><br />
- <ul>
+ <a name="frame_header_notes"><font size="+1">NOTES</font></a><br />
+ <ol>
+ <li>
+ This bit must remain reserved for <tt>0</tt> in order for a FLAC frame's initial 15 bits to be distinguishable from the start of an MPEG audio frame (<a href="http://lists.xiph.org/pipermail/flac-dev/2008-December/002607.html">see also</a>).
+ </li>
<li>
- The blocksize bits 0000-0101 and 1000-1111 may only be used if the blocksize is fixed throughout the entire stream. Blocksize bits 0110-0111 may be used in any case but the decoder will have to pessimistically guess that it is a variable-blocksize stream unless it has STREAMINFO metadata and the min_blocksize and max_blocksize values in it match. There is only one special case: the encoder may use blocksize bits 0110-0111 on the last frame of a fixed-blocksize stream, as long as the blocksize is not greater than the stream blocksize.
+ The "blocking strategy" bit must be the same throughout the entire stream.
+ </li>
+ <li>
+ The "blocking strategy" bit determines how to calculate the sample number of the first sample in the frame. If the bit is <tt>0</tt> (fixed-blocksize), the frame header encodes the frame number as above, and the frame's starting sample number will be the frame number times the blocksize. If it is <tt>1</tt> (variable-blocksize), the frame header 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 stream blocksize; its starting sample number will be calculated as the frame number times the previous frame's blocksize, or zero if it is the first frame).
</li>
<li>
The "UTF-8" coding used for the sample/frame number is the same variable length code used to store compressed UCS-2, extended to handle larger input.
</li>
- </ul>
+ </ol>
</td>
</tr>
</table>
Residual coding method:<br />
<ul>
<li>
- <tt>00</tt> : partitioned rice coding
+ <tt>00</tt> : partitioned Rice coding with 4-bit Rice parameter; RESIDUAL_CODING_METHOD_PARTITIONED_RICE follows
+ </li>
+ <li>
+ <tt>01</tt> : partitioned Rice coding with 5-bit Rice parameter; RESIDUAL_CODING_METHOD_PARTITIONED_RICE2 follows
</li>
<li>
- <tt>01-11</tt> : reserved
+ <tt>10-11</tt> : reserved
</li>
</ul>
</td>
</tr>
<tr>
<td align="right" valign="top" bgcolor="#F4F4CC">
- <a href="#partitioned_rice"><i>RESIDUAL_CODING_METHOD_PARTITIONED_RICE</i></a>
+ <a href="#partitioned_rice"><i>RESIDUAL_CODING_METHOD_PARTITIONED_RICE</i></a> ||<br />
+ <a href="#partitioned_rice2"><i>RESIDUAL_CODING_METHOD_PARTITIONED_RICE2</i></a>
</td>
<td>
</td>
</tr>
+ </table>
+ </td></tr></table>
+</div>
+
+<br />
+
+<div class="box">
+ <table width="100%" border="0" cellspacing="0" cellpadding="0" bgcolor="#EEEED4"><tr><td>
+ <table width="100%" border="1" bgcolor="#EEEED4">
+ <tr>
+ <td colspan="2" bgcolor="#D3D4C5">
+ <a name="partitioned_rice"><font size="+1"><b>RESIDUAL_CODING_METHOD_PARTITIONED_RICE</b></font></a>
+ </td>
+ </tr>
<tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <4>
+ </td>
<td>
+ Partition order.
</td>
- <td bgcolor="#F4F4CC">
- <font size="+1">NOTES</font><br />
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <a href="#rice_partition"><i>RICE_PARTITION</i></a>+
+ </td>
+ <td>
+ There will be 2^order partitions.
+ </td>
+ </tr>
+ </table>
+ </td></tr></table>
+</div>
+
+<br />
+
+<div class="box">
+ <table width="100%" border="0" cellspacing="0" cellpadding="0" bgcolor="#EEEED4"><tr><td>
+ <table width="100%" border="1" bgcolor="#EEEED4">
+ <tr>
+ <td colspan="2" bgcolor="#D3D4C5">
+ <a name="rice_partition"><font size="+1"><b>RICE_PARTITION</b></font></a>
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <4(+5)>
+ </td>
+ <td>
+ Encoding parameter:<br />
+ <ul>
+ <li>
+ <tt>0000-1110</tt> : Rice parameter.
+ </li>
+ <li>
+ <tt>1111</tt> : Escape code, meaning the partition is in unencoded binary form using n bits per sample; n follows as a 5-bit number.
+ </li>
+ </ul>
+ </td>
+ </tr>
+ <tr>
+ <td align="right" valign="top" bgcolor="#F4F4CC">
+ <?>
+ </td>
+ <td>
+ Encoded residual. The number of samples (n) in the partition is determined as follows:<br />
<ul>
<li>
- Currently, FLAC specifies only one entropy coding method.
+ if the partition order is zero, n = frame's blocksize - predictor order
+ </li>
+ <li>
+ else if this is not the first partition of the subframe, n = (frame's blocksize / (2^partition order))
+ </li>
+ <li>
+ else n = (frame's blocksize / (2^partition order)) - predictor order
</li>
</ul>
</td>
<table width="100%" border="1" bgcolor="#EEEED4">
<tr>
<td colspan="2" bgcolor="#D3D4C5">
- <a name="partitioned_rice"><font size="+1"><b>RESIDUAL_CODING_METHOD_PARTITIONED_RICE</b></font></a>
+ <a name="partitioned_rice2"><font size="+1"><b>RESIDUAL_CODING_METHOD_PARTITIONED_RICE2</b></font></a>
</td>
</tr>
<tr>
</tr>
<tr>
<td align="right" valign="top" bgcolor="#F4F4CC">
- <a href="#rice_partition"><i>RICE_PARTITION</i></a>+
+ <a href="#rice2_partition"><i>RICE2_PARTITION</i></a>+
</td>
<td>
There will be 2^order partitions.
<table width="100%" border="1" bgcolor="#EEEED4">
<tr>
<td colspan="2" bgcolor="#D3D4C5">
- <a name="rice_partition"><font size="+1"><b>RICE_PARTITION</b></font></a>
+ <a name="rice2_partition"><font size="+1"><b>RICE2_PARTITION</b></font></a>
</td>
</tr>
<tr>
<td align="right" valign="top" bgcolor="#F4F4CC">
- <4(+5)>
+ <5(+5)>
</td>
<td>
Encoding parameter:<br />
<ul>
<li>
- <tt>0000-1110</tt> : Rice parameter.
+ <tt>0000-11110</tt> : Rice parameter.
</li>
<li>
- <tt>1111</tt> : Escape code, meaning the partition is in unencoded binary form using n bits per sample; n follows as a 5-bit number.
+ <tt>11111</tt> : Escape code, meaning the partition is in unencoded binary form using n bits per sample; n follows as a 5-bit number.
</li>
</ul>
</td>
<div class="copyright">
- Copyright (c) 2000,2001,2002,2003,2004,2005,2006 Josh Coalson
+ <!-- @@@ oh so hacky -->
+ <table>
+ <tr>
+ <td align="left">
+ Copyright (c) 2000,2001,2002,2003,2004,2005,2006,2007,2008,2009 Josh Coalson
+ </td>
+ <td width="1%" align="right">
+ <a href="http://sourceforge.net"><img src="http://sflogo.sourceforge.net/sflogo.php?group_id=13478&type=1" width="88" height="31" border="0" alt="SourceForge.net Logo" /></a>
+ </td>
+ <td width="1%" align="right">
+ <a href="http://www.eff.org/cafe/"><img src="images/cafebug.gif" alt="CAFE Logo" border="0" /></a><br />
+ </td>
+ <td width="1%" align="right">
+ <a href="http://validator.w3.org/check?uri=referer"><img src="http://www.w3.org/Icons/valid-xhtml10" alt="Valid XHTML 1.0!" height="31" width="88" border="0" hspace="0" /></a>
+ </td>
+ </tr>
+ </table>
</div>
</body>
projects / platform / upstream / flac.git / blobdiff