[FFmpeg-devel] [PATCH] libavformat/avc.c annexbparsing corrupts packets

[Michael Niedermayer]

On Wed, Jul 29, 2009 at 01:15:12PM +0200, matteo elli wrote:
> > code in libavformat/avc.c is seldom executed but it surely does when you
> transmux (vcodec=copy) from h264 in a ts container to h264 in an
> mp4/mov/mkv/avi container.
> >
> > The code there fails to handle annexb 00 00 01 NAL three byets prefixes
> properly and cuts the last byte in the previous NAL corrupting the whole
> frame.
> 
> please provide a reproduceable testcase
> 
> ...
> 
> ok I have arranged a little testcase, see these files:
> 
> http://www.m-elli.com/annexb-test.ts 
> 
> the original ts file
> 
> http://www.m-elli.com/annexb-test-ffmpeg-0.5.mp4 
> 
> the original ts file processed by ffmpeg-0.5 without patch (command "ffmpeg
> -i annexb-test.ts -vcodec copy -an -f mp4 annexb-test-ffmpeg-0.5.mp4")
> 
> http://www.m-elli.com/annexb-test-ffmpeg-0.5-patched.mp4 
> 
> the original ts file processed by ffmpeg-0.5 with patch (command "ffmpeg -i
> annexb-test.ts -vcodec copy -an -f mp4 annexb-test-ffmpeg-0.5-patched.mp4")
> 
> http://www.m-elli.com/annexb-test-nal-tree.txt 
> 
> the NAL tree generated with H264Visa from the original ts file, I have
> commented the first pict comparing lengths to the annexb-test-ffmpeg-0.5.mp4
> file like this:
> 
> + NAL(Pic No. in decoding order)
>     + Before First Picture
>         + NAL Type: AUD, Len: 2, Pos: 10(0xa)
>     + Pic 1(Dec Order)
>         + NAL Type: SPS, Len: 25, Pos: 19(0x13)
>         + NAL Type: PPS, Len: 4, Pos: 48(0x30)
>         + NAL Type: SEI, Len: 11, Pos: 56(0x38)   -> becomes len 12 (0x0c)
>         + NAL Type: IDR, Len: 35837, Pos: 71(0x47)  -> becomes len 35836
> (0x8bfc) -> one byte truncated !!!
>         + NAL Type: IDR, Len: 37451, Pos: 35912(0x8c48)  -> becomes len
> 37452 (0x924C)
>         + NAL Type: IDR, Len: 38904, Pos: 73371(0x11e9b) -> becomes len
> 38908 (0x97fc)
>         + NAL Type: IDR, Len: 39717, Pos: 112279(0x1b697) -> becomes len
> 39716 (0x9b24) -> one byte truncated !!!
>         + NAL Type: IDR, Len: 61112, Pos: 152003(0x251c3) -> becomes len
> 61116 (0xeebc)
>         + NAL Type: IDR, Len: 31483, Pos: 213125(0x34085) -> becomes len
> 31489 (0x7b01)
> 
> as you can see NAL lengths are wrong, this is usually not an issue when len
> is greater but in slices 1 and 4 one byte is missing and the whole pict gets
> corrupted

no corruption is reproduceable
there may be bugs but this is not a useable bugreport

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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