128 lines
5.0 KiB
Markdown
128 lines
5.0 KiB
Markdown
# Group subset
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The FLAC format specifies a subset of itself to ensure
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streamability and limits the decoding requirements for hardware
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implementations. The reference FLAC encoder will enforce this
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subset unless specifically disabled.
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The files in this group are considered a baseline for general
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decoders: these files should be properly decoded or properly
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rejected before playback is attempted by any decoder. A
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decoder can choose to reject certain files, for example
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multichannel files, files with high or unusual samplerates,
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files with a high bit depth. Crashing or mangled playback of
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these files is probably going to be noticed by unsuspecting
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users of a decoder. Read the README.txt in the directory
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subset for details on each file.
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## Files \#1 - \#27
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The first 10 files tests 44.1kHz, 16-bit audio with various
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blocksizes that are within subset.
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Files 11 through 23 tests the ability to decode FLAC files
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with various features that are within subset but aren't used
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often.
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- File 11 uses the maximal allowed rice partition order (8)
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- File 12 uses the maximal allowed qlp precision (15)
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- File 13 uses the smallest sane qlp precision (2)
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- File 14 uses wasted bits
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- File 15 uses only 'verbatim' frames
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- File 16 uses rice escape codes and partition order 8
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- File 17 uses all possible fixed orders (especially order 0 which isn't used often)
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- File 18 is encoded with precision search, using qlp precisions between 3 and 15
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- File 19 uses a samplerate of 35467Hz
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- File 20 uses a samplerate of 39kHz
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- File 21 uses a samplerate of 22050Hz
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- File 22 has 12 bits per sample
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- File 23 has 8 bits per sample
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Files 24 through 27 test the ability to decode a FLAC file with
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a variable blocksize. This is a subset feature which is
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currently (August 2021) only implemented in the Flake decoder
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and its forks/decendants and is not enabled by default.
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With the release of FLAC 1.2.0 in July 2007, the FLAC
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specification was augmented to more clearly signal variable
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blocksize streams by the use of a special bit in the header.
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File 24, 25 and 26 use this format. File 27 follows the old
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specification, which is much harder to detect
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- File 24 uses the current format and is created by flake r264
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- File 25 uses the current format and is created by a modified flake r264 creating smaller blocks
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- File 26 uses the current format and is created by CUETools.Flake 2.1.6
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- File 27 uses the old format and is created by flake 0.11
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## Files \#28 - \#37
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Files 28 through 37 test the ability to decode various
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high-resolution FLAC file (96kHz, 24-bit)
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- File 28 uses default settings
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- File 29 uses the largest allowed blocksize (16384)
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- File 30 uses non-standard blocksize 13456
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- File 31 uses only 32th order predictors
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- File 32 uses escape codes and partition order 8
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- File 33 is upsampled to 192kHz
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- File 34 is upsampled to 192kHz, uses blocksize 16384, 32th
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order predictors only, maximum LPC precision and maximum
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partition order
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- File 35 uses non-standard samplerate 134560Hz
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- File 36 is upsampled to 384kHz
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- File 37 has 20 bits per sample
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## Files \#38 - \#44
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Files 38 through 43 test the ability to decode various
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multichannel FLAC files. Each file contains a voice description
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of the channels present, so as to see whether the channels are
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decoded in the correct lay-out.
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- File 38 is 3.0-channel (left, right, center)
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- File 39 is 4.0-channel or quadraphonic
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- File 40 is 5.0-channel
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- File 41 is 5.1-channel
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- File 42 is 6.1-channel
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- File 43 is 7.1-channel
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File 44 tests the ability to decode a file with the highest
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possible data input per second, staying within subset and using
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a standard samplerate. It also only uses 32th order predictors
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at the highest possible predictor precision and the largest
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blocksize allowed within the FLAC subset making it especially
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challenging to decode.
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## Files \#45 - \#59
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Files 45 through 59 test the ability to handle various streams
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with valid but rather unusual or extreme metadata.
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- File 45 has 'unknown number of samples' in STREAMINFO
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- File 46 has maximum and minimum framesize set to 'unknown'
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- File 47 has only a STREAMINFO block
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- File 48 has an extremely large SEEKTABLE
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- File 49 has an extremely large PADDING block
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- File 50 has an extremely large PICTURE block (JPG of 15.8MB)
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- File 51 has an extremely large VORBISCOMMENT block
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- File 52 has an extremely large APPLICATION block
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- File 53 has a CUESHEET block with absurdly many indexes
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- File 54 with the same 20 VORBISCOMMENTs repeated 1000 times
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- File 55 has the metadata of track 47-52 combined
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- File 56 has a PICTURE with mimetype image/jpeg
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- File 57 has a PICTURE with mimetype image/png
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- File 58 has a PICTURE with mimetype image/gif
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- File 59 has a PICTURE with mimetype image/avif
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## Files \#60 - \#64
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Miscellaneous, later additions
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- File 60 is mono audio
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- File 61, 62 and 63 are signals with rather extreme
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characteristics that might trigger overflow if a decoder
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uses 32-bit integers to calculate the predictor where 64-bit
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integers are appropriate
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- File 64 contains rice codes with escape code zero
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