Bug#863663: libgstreamer1.0-0: plays MJPEG AVI files (and possibly other formats) at degraded quality

[Francesco Poli]

On Tue, 20 Jun 2017 08:55:41 +0300 Sebastian Dröge wrote:

> On Sun, 2017-06-18 at 13:01 +0200, Francesco Poli wrote:
> > [...]
> >   jpegdec     → rank 256
> >   avdec_mjpeg → rank 64
> > 
> > It then sets swapped ranks with set_rank() :
> > 
> >   jpegdec     → rank 64
> >   avdec_mjpeg → rank 256
> > 
> > which are checked again and found to be set as desired.
> > 
> > Nonetheless, the AVI file is still played at degraded quality,
> > as if nothing had changed at all.
> 
> The problem here is that avdec_mjpeg needs jpegparse, jpegdec doesn't.
> And jpegparse has a rank of 0, so will never be automatically used.
> 
> Try setting the jpegparse rank to 256 too, avdec_mjpeg to 256 and
> jpegdec to 0.

I have just tried, but it does not seem to work.   :-(

I have also added the setting of videoconvert rank to 256 (it was 0),
since the manual pipeline that worked with gst-launch-1.0 also included
videoconvert.

The debug output (the format was slightly changed) was:

  accessing the GStreamer registry...
  jpegdec rank changed from 256 to 0
  avdec_mjpeg rank changed from 64 to 256
  jpegparse rank changed from 0 to 256
  videoconvert rank changed from 0 to 256
  
  Gstreamer error Your GStreamer installation is missing a plug-in.
  Gstreamer error Internal data stream error.

As you can see, setting jpegdec rank to 0 causes GStreamer to complain
about a missing plug-in and no movie is played.   :-(

If I instead set jpegdec rank to 64, I get no error, but the movie is
again played at degraded quality (showing that jpegdec is again
magically selected, despite having lower rank than everything else!).

The debug output was:

  accessing the GStreamer registry...
  jpegdec rank changed from 256 to 64
  avdec_mjpeg rank changed from 64 to 256
  jpegparse rank changed from 0 to 256
  videoconvert rank changed from 0 to 256


At this point I really cannot understand what's going on and why all my
attempts are failing...   :-(


-- 
 http://www.inventati.org/frx/
 There's not a second to spare! To the laboratory!
..................................................... Francesco Poli .
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