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authorAndreas Rheinhardt <andreas.rheinhardt@gmail.com>2019-12-28 10:00:37 +0100
committerAndreas Rheinhardt <andreas.rheinhardt@gmail.com>2020-03-30 04:23:06 +0200
commite6ea75a38de192c3133b9eebe603979bffeed20b (patch)
tree291be7a965aeff3ea2355a8e6eeb88f4265b4ff3 /libavutil/md5.c
parent72be5d4661685ecaca372eae78b50e1583e4dab9 (diff)
downloadffmpeg-e6ea75a38de192c3133b9eebe603979bffeed20b.tar.gz
avformat/matroskaenc: Improve calculating EBML ID size
When the Matroska muxer writes an EBML ID, it calculates the length of said ID before; and it does this as if this were a number that needs to be encoded as EBML number: The formula used is (av_log2(id + 1) - 1) / 7 + 1. But the constants used already contain the VINT_MARKER (the leading bit indicating the length of the EBML number) and therefore the algorithm used makes no sense. Instead the position of the most significant byte set gives the desired length. The algorithm used until now worked because EBML numbers are subject to restrictions: If the EBML number takes up k bytes, then the bit 1 << (7 * k) is set and av_log2(id) is 7 * k. So the current algorithm produces the correct result unless the EBML ID is of the form 7 * k - 1 because of the "id + 1". But contrary to encoding lengths as EBML number (where the + 1 exists to avoid the encodings reserved for unknown length), such EBML numbers are simply forbidden as EBML IDs and as such none of them were ever written. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Diffstat (limited to 'libavutil/md5.c')
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