[Ffmpeg-devel] [Ffmpeg-devel-old] Huffman Limits

Michael Niedermayer michaelni
Sun Mar 12 04:34:16 CET 2006


On Sat, Mar 11, 2006 at 06:38:41PM -0800, Mike Melanson wrote:
> Hi,
> 	Are there any limits on Huffman tables in FFmpeg? I guess I am 
> 	asking about codeword sizes. There are some tables in AAC where the 
> codewords reach up to 19 bits it size. But then, SVQ1 has some 22-bit 
> codewords and FFmpeg seems to have no trouble handling those. Are there any 
> special concerns with larger codeword sizes?

init_vlc() should work fine with upto 32bit long codewords, for larger ones
it should be a matter of int->uint64_t but so far no codec needed >32

get_vlc2() is currently limited to a max of table depth of 3, so that puts
a bits_per_table*3 limit on the codeword size, bits_per_table is 9 commonly
this also hasnt been an issue, increasing this limit is a matter of adding 5
lines or so to GET_VLC


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