[FFmpeg-devel] [PATCH] lavf/utils: reset event_flags if extradata is not extracted correctly

[Anton Khirnov]

Quoting Linjie Fu (2021-01-30 07:44:09)
> On Mon, Jan 25, 2021 at 9:08 PM Anton Khirnov <anton at khirnov.net> wrote:
> >
> > Quoting Linjie Fu (2021-01-25 04:49:21)
> > > On Mon, Jan 25, 2021 at 12:49 AM Anton Khirnov <anton at khirnov.net> wrote:
> > > >
> > > > Quoting Linjie Fu (2021-01-24 16:05:56)
> > > > > Regression since 87f0c8280.
> > > > >
> > > > > If the extradata of a stream could not be extracted correctly,
> > > > > codec_info_nb_frames would remain zero, while st->event_flag would still
> > > > > be marked as AVSTREAM_EVENT_FLAG_NEW_PACKETS.
> > > > >
> > > > > The two expressions could be different in this case, hence reset
> > > > > event_flags and calculate the correct score.
> > > > >
> > > > > Fix #9029.
> > > >
> > > > The ticket mentions ffplay, but ffplay does not access event_flags.
> > > >
> > >
> > > You are right, this helps ffmpeg cmdline to copy and dump:
> > > $ ffmpeg -i sample_cut.flv -c copy -y dump.mp4
> > >
> > > Before 87f0c8280 and after this patch:
> > >
> > > audio streams could be dumped and playable, while video streams still not.
> > >
> > > 87f0c8280..master:
> > > Error reporting and quits.
> > >
> > > [mp4 @ 0x7fb276809a00] dimensions not set
> > > Could not write header for output file #0 (incorrect codec parameters
> > > ?): Invalid argument
> > > Error initializing output stream 0:1 --
> > >
> > > I'd change the commit message to "#9029 related" for this, since the
> > > ffplay issue remains the same.
> >
> > I am still not convinced this is really a regression. You can still
> > process the file by explicitly mapping only the audio stream.
> Okay, I'm fine with this if it won't trigger failures for to different paths.
> 
> > This file is damaged and the video stream is not readable. IMO it is
> > better to report an error and let the user decide what to do with it
> > than silently skip the video stream while pretending everything is fine.
> VLC is able to decode/play this correctly, hence maybe need to
> investigate more into this.

VLC can also play only the audio stream. ffmpeg handles it as I
described above, which seems appropriate to me.

I suppose ffplay could be changed to be more lenient about decoding
errors, but then I see ffplay mainly as a testing/development tool
rather than a serious player.

-- 
Anton Khirnov