Any progress?
> I agree. Please keep up informed. >> 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 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. >>>> 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 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'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? _______________________________________________ flac-dev mailing list flac-dev@xiph.org http://lists.xiph.org/mailman/listinfo/flac-dev
