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

[Francesco Poli]

On Wed, 07 Jun 2017 09:44:02 +0300 Sebastian Dröge wrote:

> On Thu, 2017-06-01 at 23:47 +0200, Francesco Poli wrote:
[...]
> > I tried with
> > 
> >   $ gst-launch-1.0 filesrc location=wave_anim.avi \! avidemux \!
> > avdec_mjpeg \! autovideosink
> >   $ gst-launch-1.0 filesrc location=wave_anim.avi \! avdec_mjpeg \!
> > autovideosink
> > 
> > to no avail.
> > Both pipelines abort with errors (although they spit different error
> > messages).
> 
> The first, but with adding jpegparse between avidemux and avdec_mjpeg
> should work. And potentially adding a videoconvert before
> autovideosink.

Thanks, I can confirm that

  $ gst-launch-1.0 filesrc location=wave_anim.avi \! avidemux \! jpegparse \! avdec_mjpeg \! videoconvert \! autovideosink

works as expected (quality nearly identical to mpv and to ffplay).

[...]
> > Which is the feature that corresponds to avdec_mjpeg?
> > Which is the one corresponding to jpegdec?
> 
> You could get them from the registry by exactly those names with
> gst_registry_find_feature(). The type is GST_TYPE_ELEMENT_FACTORY.

Mmmh, I suppose that this is translatable into Vala, if the application
is written in Vala...

At least, by looking at "gstreamer-1.0.vapi", I see that there is a
method named find_feature() in the class Registry of namespace Gst and
a method set_rank() in the class PluginFeature of namespace Gst.
I have to figure out how to use them, since I am not familiar at all
with Vala (are you able to help me, by chance?), but that's another
story!


As an alternative, is there some configuration file that the user can
tweak in order to adjust the ranks of jpegparse and avdec_mjpeg,
without modifying the application that uses the GStreamer library?


I really hope we can find a workaround soon (and, in the meanwhile, I
also hope that the actual bug gets a proper fix).

-- 
 http://www.inventati.org/frx/
 There's not a second to spare! To the laboratory!
..................................................... Francesco Poli .
 GnuPG key fpr == CA01 1147 9CD2 EFDF FB82  3925 3E1C 27E1 1F69 BFFE
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