[Bug 793224] gl: context persistence issue

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=793224

--- Comment #2 from Philippe Normand <philn at igalia.com> ---
(In reply to Matthew Waters (ystreet00) from comment #1)
> (In reply to Philippe Normand from comment #0)
> > I have an issue where my custom playbin video sink (glupload !
> > glcolorconvert ! appsink) loses its context when the video chain is removed
> > from playsink while the whole pipeline goes to READY.
> > 
> > So rendering works fine on first run, the app handles the need-context
> > message fine. On second run the gl elements try a context query, that fails.
> > Then they try to post a need-context message but they have no bus associated
> > yet, so that fails. Then a new display is created from
> > gst_gl_ensure_element_data() and it's for the wrong platform (egl vs
> > wayland).
> 
> wayland only works with egl. Do you mean glx vs egl or x11 vs wayland ?
> 

The latter

> There's also an issue of terminology. When you say GL context, do you mean
> the GStreamer GL context created internally or an application provided GL
> context (they are not the same thing).
> 

The application provided GL context

> I think the key thing here is that 'there is not bus associated yet' which
> sounds problematic.  Is the lack of a bus a playsink/playbin or an
> application issue.
> 

I don't think it's an application issue ;) Upon EOS I sent the playbin state to
READY and to PLAYING again.

> > But even with all those failures, somehow rendering works if the pipeline
> > goes to PLAYING again.
> 
> 'somehow'?
> 

It's strange because the GL app context remains valid for two runs and not
more, I don't have an explanation for this yet.

> > On third run rendering fails.
> 
> How exactly?
> 

I can see a scrambled frame for half a second and then the rendering area goes
black although the pipeline runs until EOS.

> > As a workaround I can manually set the context on the video sink before
> > going to PAUSED on second and following runs but shouldn't the gl context be
> > automatically reused from the persistent element context?
> 
> The GL context is not a persistent resource so will be destroyed and
> recreated on pipeline shutdown/restart which is also true if playsink sets
> the video sink to NULL. 

Ok so the GL app context should be requested again at restart then?

> GstContext's are also removed from elements when
> set they are set to NULL (or READY). I can't remember which.
> 

Non-persitent GstContexts are removed when the element goes to NULL.

> I think in order to debug this in any sort of capacity, some logs are
> needed. e.g. GST_DEBUG=3,gl*:7,*CONTEXT*:7

Ok I'm attaching a log file, the video played is 6 seconds long and 3 playback
attempts are made.

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