[FFmpeg-devel] [PATCH] avformat/mxfenc: Never set codec_ul UID to NULL

[Baptiste Coudurier]

Hi Andreas,

> On Mar 2, 2020, at 10:14 AM, Tomas Härdin <tjoppen at acc.umu.se> wrote:
> 
> fre 2020-02-28 klockan 05:14 +0100 skrev Andreas Rheinhardt:
>> mxf distinguishes codec profiles by different UIDs and therefore needs
>> to check that the input is actually compatible with mxf (i.e. if there
>> is a defined UID for it). If not, then sometimes the UID would be set to
>> NULL and writing the (video) packet would fail. Yet the following audio
>> packet would trigger writing the header (which has been postponed because
>> the UID is not known at the start) and if the UID is NULL, this can lead
>> to segfaults. This commit therefore stops setting the UID to NULL if the
>> input is incompatible with mxf (it has initially been set to a generic
>> value in mxf_write_header()).
>> 
>> Fixes #7993.
>> 
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>> ---
>> a) #7993 is actually a segfault even if its description suggests
>> otherwise.
>> b) My actually preferred way to fix this was to error out if an audio
>> packet is encountered and the header has not been written yet, thereby
>> ensuring that only a video packet can trigger writing the header and
>> said code is only reached when the video is actually compatible with mxf
>> (or with this muxer?). Yet I was surprised to find out that the
>> FATE-test mxf-d10-user-comments would fail with this, because right now
>> writing the header in this test is triggered by an audio packet (the
>> video packets aren't written because they are not of the right size) and
>> if these aren't written either, there will be zero bytes of output.

Yes, we need the video track before writing the header. It’s an issue and that’s
 what should be implemented IMHO.

— 
Baptiste