[FFmpeg-devel] [PATCH 3/3] avcodec/mpeg4_unpack_bframes_bsf: Improve DivX userdata check

Michael Niedermayer michael at niedermayer.cc
Mon Feb 4 20:43:25 EET 2019

On Sat, Feb 02, 2019 at 08:34:12PM +0100, Andreas Rheinhardt wrote:
> The earlier version didn't really check that the 'p' of a "p\0" is
> actually part of a DivX user_data section, instead it treated the first
> "p\0" after the start of a user_data section as end of a DivX user_data
> section if it is close enough to the beginning of the user_data section;
> it actually needn't be part of a user_data section at all.
> Furthermore, the code worked under the assumption that there is a 0x00
> after the 'p' although this might not be true for extradata if the DivX
> user_data unit is at the end of the extradata.
> Both of these flaws have been fixed.

The absence of a check for DivX was intentional so other codecs could
also generate packed bitstreams and be supported.

extradata generally has 0 value padding bytes at the end. But yes it
would be better to avoid depending on that.


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Observe your enemies, for they first find out your faults. -- Antisthenes
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