[FFmpeg-devel] [PATCH 1/2] libavformat/mxfenc.c: Fix segfault when writing an audio packet when there has not been a video one.

[Alexis Ballier]

On Wed, 21 Oct 2015 22:43:04 +0200
Tomas Härdin <tomas.hardin at codemill.se> wrote:

> On Tue, 2015-10-20 at 16:43 +0200, Marton Balint wrote:
> > On Mon, 19 Oct 2015, Tomas Härdin wrote:
> >   
> > > On Mon, 2015-10-19 at 11:40 +0200, Alexis Ballier wrote:  
> > >> On Mon, 19 Oct 2015 10:30:00 +0200
> > >> Michael Niedermayer <michael at niedermayer.cc> wrote:
> > >>  
> > >>> On Fri, Oct 16, 2015 at 10:42:32AM +0200, Alexis Ballier
> > >>> wrote:  
> > >>>> This happens when writing the trailer of a file containing
> > >>>> audio but that has not muxed any video packet. Fixes ticket
> > >>>> #4817.
> > >>>>
> > >>>> ----  
> > >>>
> > >>> from IRC:
> > >>> <thardin> maybe it should print a warning that there has been no
> > >>> video?  
> > >>
> > >> maybe, but what would be the right condition ? just this case ?
> > >> or when writing any edit unit without video? or... ?
> > >> I haven't been able to find clear references on this (well,
> > >> those smpte specs I googled aren't esp. easy to read either),
> > >> but e.g. the muxer refuses to mux without exactly one video
> > >> stream, so maybe, an empty video stream is also an error; I
> > >> don't know  
> > >
> > > I'm not particularly fond of second-guessing these kinds of
> > > things. D-10 is really anal about what constitutes a legal file,
> > > so it's probably best not to write anything if something seems
> > > amiss. In the end, the real test for correctness is whether the
> > > output works with all gear for your particular use case. But
> > > segfaults are important to fix, so I'm not too concerned here.
> > > Plus my main concern is mxfdec, not mxfenc. 
> > 
> > Why not simply return error and print an error explaining "An audio
> > packet was muxed before a video, this is not supported."
> > 
> > Segfault -> error is much better than segfault -> possibly broken
> > file.  
> 
> Yes, simply bailing out is infinitely better than segfaulting. It's
> also the more conservative approach, which I am for

ok, so assuming the error condition is 'muxing first audio packet
before first video packet (if any)', I'll re-send with that warning
added