>>>>>>>>> I'm misleading about FLAC subset constraints... Please help me >>>>>>>>> understand exact FLAC subset limitation. >>>>>>>>> >>>>>>>>> From >>>>>>>>> https://www.xiph.org/flac/documentation_tools_flac.html#flac_options_blocksize: >>>>>>>>> >>>>>>>>> Subset streams must use one of >>>>>>>>> 192/576/1152/2304/4608/256/512/1024/2048/4096 (and 8192/16384 if the >>>>>>>>> sample rate is >48kHz). The reference encoder uses the same block size >>>>>>>>> for the entire stream. >>>>>>>>> >>>>>>>>> From https://www.xiph.org/flac/format.html#subset: >>>>>>>>> >>>>>>>>> The blocksize must be <=16384; if the sample rate is <= 48000Hz, the >>>>>>>>> blocksize must be <=4608. >>>>>>>>> >>>>>>>>> Finally, "one of 192/576/1152/2304/4608/256/512/1024/2048/4096" or >>>>>>>>> just (simply) "<=4608", "one of 8192/16384" or just "<=16384"? >>>>>>>>> >>>>>>>>> Maximum (4608) value and any intermediate values are not one of >>>>>>>>> 192/576/1152/2304/4608/256/512/1024/2048/4096. >>>>>>>>> >>>>>>>>> The first statement is more restricted. >>>>>>>>> >>>>>>>>> Is the word "must" to be interpreted as described in RFC 2119 >>>>>>>>> (http://www.ietf.org/rfc/rfc2119.txt)? >>>>>>>>> >>>>>>>>> The second question: >>>>>>>>> >>>>>>>>> From https://www.xiph.org/flac/documentation_format_overview.html: >>>>>>>>> >>>>>>>>> The reference encoder uses a single block size for the whole stream >>>>>>>>> but the FLAC format does not require it. >>>>>>>>> >>>>>>>>> Should stream MUST have constant (fixed) block size (if blocksize >>>>>>>>> satisfies all restrictions from first question) to be subset? >>>>>>>>> >>>>>>>>> Is variable block size stream (if blocksize satisfies all restrictions >>>>>>>>> from first question) be subset? >>>>>>>>> >>>>>>>>> The third question: >>>>>>>>> >>>>>>>>> Is FLAC files compressed by FFMPEG with "-compression_level 12" switch >>>>>>>>> are subset?
>>>>>>>> I don't understand what it is you don't get about those blocksizes. For >>>>>>>> subset streams, the blocksize has to be one of 576/1152/2304/4608 or >>>>>>>> 256/512/1024/2048/4096 if the samplerate is lower then or equal to >>>>>>>> 48kHz, if higher, 8192 and 16384 are allowed too. If you use any other >>>>>>>> blocksize, the stream is not subset compliant. >>>>>>>> >>>>>>>> Considering the fixed or variable blocksize stuff, the subset does not >>>>>>>> restrict that, so using a variable blocksize is technically subset >>>>>>>> compliant. However, flake does warn when using variable blocksizes that >>>>>>>> the stream is not subset compliant. The thing is, it's not in the >>>>>>>> reference encoder, so probably most (hardware) decoders haven't been >>>>>>>> tested with it. If you want to be safe, you should probably restrict >>>>>>>> yourself to a fixed-blocksize stream. >>>>>>>> >>>>>>>> Finally, ffmpeg level 12 is not subset compliant. >>>>>>> I mean that the first statement [Subset streams must use one of >>>>>>> 192/576/1152/2304/4608/256/512/1024/2048/4096 (and 8192/16384 if the >>>>>>> sample rate is >48kHz).] published on >>>>>>> https://www.xiph.org/flac/documentation_tools_flac.html#flac_options_blocksize >>>>>>> page IS NOT EQUAL to second statement [The blocksize bits in the frame >>>>>>> header must be 0001-1110. The blocksize must be <=16384; if the sample >>>>>>> rate is <= 48000Hz, the blocksize must be <=4608.] published on >>>>>>> https://www.xiph.org/flac/format.html#subset page. >>>>>>> >>>>>>> What statement (first or second) is right? >>>>>>> >>>>>>> 0001-1110 mean 0110 and 0111 too??? (0110 mean "get 8 bit >>>>>>> (blocksize-1) from end of header", 0111 mean "get 16 bit (blocksize-1) >>>>>>> from end of header") >>>>>>> >>>>>>> Why you don't use STRICT block size checking in >>>>>>> FLAC__format_blocksize_is_subset() like this: >>>>>>> >>>>>>> FLAC_API FLAC__bool FLAC__format_blocksize_is_subset(unsigned >>>>>>> blocksize, unsigned sample_rate) >>>>>>> { >>>>>>> if(blocksize == 192 || blocksize == 576 || blocksize == 1152 >>>>>>> || blocksize == 2304 || blocksize == 4608 || blocksize == 256 || >>>>>>> blocksize == 512 || blocksize == 1024 || blocksize == 2048 || >>>>>>> blocksize == 4096 || (sample_rate > 48000 && (blocksize == 8192 || >>>>>>> blocksize == 16384))) >>>>>>> return true; >>>>>>> else >>>>>>> return false; >>>>>>> } >>>>>>> >>>>>>> instead of >>>>>>> >>>>>>> FLAC_API FLAC__bool FLAC__format_blocksize_is_subset(unsigned >>>>>>> blocksize, unsigned sample_rate) >>>>>>> { >>>>>>> if(blocksize > 16384) >>>>>>> return false; >>>>>>> else if(sample_rate <= 48000 && blocksize > 4608) >>>>>>> return false; >>>>>>> else >>>>>>> return true; >>>>>>> } >>>>>>> >>>>>>> FLAC__format_blocksize_is_subset from format.c IS NOT EQUAL to my >>>>>>> code. E.g. FLAC__format_blocksize_is_subset(1536, 44100) from format.c >>>>>>> returns true, but 1536 is not subset blocksize because 1536 is not one >>>>>>> of 192/576/1152/2304/4608/256/512/1024/2048/4096! >>>>>> I think you've found a bug, Bart. >>>>>> >>>>>> flac 1.2.1 did not have any FLAC__format_blocksize_is_subset() function, >>>>>> so >>>>>> the source you're seeing in format.c must be new. If the format >>>>>> documentation you linked to is correct, then either the specifications >>>>>> are >>>>>> self-contradictory, or the code is not implementing the subset checks as >>>>>> described. My interpretation is that blocksize bits of 0110 and 0111 >>>>>> would >>>>>> not be included in the subset. The whole point of the subset is to have a >>>>>> small and finite list of values so that embedded decoders do not have to >>>>>> deal with every possible block size. >>>>>> >>>>>> This bears further investigation. >>>>> FLAC__format_blocksize_is_subset() was introduced by commit #8ab0138 >>>>> (https://gitorious.org/flac/flac/commit/8ab013837d379d3d1fa84eac5420faec41852fd7) >>>>> over 5 years ago and available in the latest stable release 1.3.0. >>>>> >>>>> It would be nice if the official FLAC documentation used common >>>>> adopted (used) math notation: math intervals (left-open, right-open, >>>>> open, left-closed, right-closed, closed) e.g. "[0010, 0101] ∪ [1000, >>>>> 1110]" or simply math sets e.g. "{0010, 0011, 0100, 0101, 1000, 1001, >>>>> 1010, 1011, 1100, 1101, 1110}" (if number of elements in not too big) >>>>> instead of current nonstrict notation e.g. "0001-1110" to >>>>> disambiguate. >>>>> >>>>> There are other ambiguities in official FLAC documentation. >>>>> >>>>> It would be nice if FLAC project had its own doc wiki. >>>>> >>>>> Should I open a bug ticket? >>>>> >>>>> Please keep me informed on your investigation. >>>> I agree. Please keep up informed. >>> Any progress? >> http://git.xiph.org/?p=flac.git;a=commit;h=09229aa967251ce840e43d300d27a915495e75db >> commit 2007-07-31, author: Josh Coalson, committer: Josh Coalson >> >> "document blocksize strategy bit, RESIDUAL_CODING_METHOD_PARTITIONED_RICE2, >> new >> subset sample rates, subset clarification, variable blocksize clarification" >> >> Before: >> "The blocksize bits in the frame header 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. If the sample rate is <= 48000Hz, the blocksize must be <=4608, >> i.e. blocksize bits 0001-0101 or 1000-1100." >> >> After: >> "The blocksize bits in the frame header must be 0001-1110. The blocksize must >> be <=16384; if the sample rate is <= 48000Hz, the blocksize must be <=4608." > Also found this: > > http://lists.xiph.org/pipermail/flac-dev/2008-May/002550.html > http://lists.xiph.org/pipermail/flac-dev/2008-May/002559.html Well, finally, any block size from following math interval [16, 191] ∪ [193, 255] ∪ [257, 511] ∪ [513, 575] ∪ [577, 1023] ∪ [1025, 1151] ∪ [1153, 2047] ∪ [2049, 2303] ∪ [2305, 4095] ∪ [4097, 4607] is subset, or not? If sample rate > 48 kHz, any block size from following math interval [16, 191] ∪ [193, 255] ∪ [257, 511] ∪ [513, 575] ∪ [577, 1023] ∪ [1025, 1151] ∪ [1153, 2047] ∪ [2049, 2303] ∪ [2305, 4095] ∪ [4097, 4607] ∪ [4609, 8191] ∪ [8193, 16383] is subset, or not? In other words, for example, 1536 is subset block size, or not? _______________________________________________ flac-dev mailing list flac-dev@xiph.org http://lists.xiph.org/mailman/listinfo/flac-dev
