[FFmpeg-devel] [PATCH] fix possible crash if vpre before vcodec

[Robert Swain]

2009/2/27 Michael Niedermayer <michaelni at gmx.at>:
> On Fri, Feb 27, 2009 at 02:54:58PM +0100, Reimar D?ffinger wrote:
>> On Fri, Feb 27, 2009 at 01:33:02PM +0000, Robert Swain wrote:
>> > 2009/2/27 Reimar D?ffinger <Reimar.Doeffinger at stud.uni-karlsruhe.de>:
>> > > On Fri, Feb 27, 2009 at 12:36:27PM +0000, Robert Swain wrote:
>> > >> 2009/2/27 Michael Niedermayer <michaelni at gmx.at>:
>> > >> > On Fri, Feb 27, 2009 at 11:25:26AM +0100, Reimar D?ffinger wrote:
>> > >> >> I recently tried the following command
>> > >> >> ffmpeg -i baldursgate-logo.mve -vpre hq -vcodec libx264 -b 500k -an out.mp4
>> > >> >> and wondered why it would not work.
>> > >> >> strace showed the following:
>> > >> >> open("/home/reimar/.ffmpeg/hq.ffpreset", O_RDONLY) = -1 ENOENT (No such file or directory)
>> > >> >> open("/home/reimar/.ffmpeg/(null)-hq.ffpreset", O_RDONLY) = -1 ENOENT (No such file or directory)
>> > >> >> open("/usr/local/share/ffmpeg/hq.ffpreset", O_RDONLY) = -1 ENOENT (No such file or directory)
>> > >> >> open("/usr/local/share/ffmpeg/(null)-hq.ffpreset", O_RDONLY) = -1 ENOENT (No such file or directory)
>> > >> >> obviously ffmpeg tries to open the file already during option parsing (this could probably be considered
>> > >> >> the real bug). When -vcodec is set only afterwards it passes NULL to
>> > >> >> snprintf %s argument which may (and will) crash with some
>> > >> >> implementations.
>> > >> >> I propose a patch that at least avoids the crash, but e.g. this:
>> > >> >> -vcodec blub -vpre hq -vcodec libx264
>> > >> >> will still have the counter-intuitive behaviour of reading
>> > >> >> blub-hq.ffpreset but encoding with libx264.
>> > >> >
>> > >> > would it not make more sense to warn the user that the codec is not set
>> > >> > before -*pre instead of silently skiping searching for the file?
>> > >>
>> > >> I agree. I prefer command lines to error out on options that don't
>> > >> work as intended than to continue on. But a warning at least is
>> > >> absolutely necessary.
>> > >>
>> > >> Also, it should be documented that the preset options should come
>> > >> after the codec name.
>> > >
>> > > Well, the warning still would not work right, as the example
>> > > -vcodec blub -vpre hq -vcodec libx264
>> > > above shows, that's why I didn't consider it particularly useful.
>> >
>> > Maybe the non-explicit codec idea wasn't so good after all. Maybe we
>> > should suggest people use -vpre libx264-hq?
>>
>> I think it was a good idea, just the implementation is not optimal.
>> I don't know FFmpeg command line parsing well, but in MPlayer I'd just
>> store the -?pre string somewhere and open the file after parsing all the
>> other options...
>
> can be done, add a static char, store it there
> then call the parsing function from new_video_stream() and others
> but beware of chains of bitstream filters ...
>
> [i hope ive not missed some detail ...]

Would that work for multiple output files?

ffmpeg -i blah ... -vpre hq -vcodec libx264 ... oufile1.mp4 -vpre blah
-vcodec foo ... outfile2.avi

What would be the behaviour if -vpre isn't specified for the second
output file? For the matter, what is the behaviour for other options
in this case? I never knew.

Regards,
Rob