gst-vaapi and opengl again

[Nicolas Dufresne]

Le mardi 12 mars 2013 à 00:13 -0700, Jorge a écrit :

> Hi Nicolas, thanks for answering!
> 
> Could you clarify a little more about the GstVideoContext and GstSurface
> role, I would like to know
> what is going on?


The GstVideoContext is used to would allow multiple thread to access and
exchange buffer on the same display. The context is first created by a
sink (for static pipeline) or a video decoder (for dynamic pipeline like
playbin2) and shared with neighbor elements at run-time. Because of the
nature of GLX, there is machanism to share an X11 display with VA
element.

the GstSurfaceBuffer is a subclass of GstBuffer (that was done before
GstMeta and/or qdata). It provides extra information (like the context)
and allow creating converter.


> About the GstVideoContext, in my little X11 application, where I open the
> display, I do the 'gst_bus_set_sync_handler'
> in order to call 'gst_video_context_set_context_pointer' and set the same
> display, but is it needed in order to create
> an opengl context in the vaapi side?


On the application side, you should watch for "prepare-video-context"
message on the sync bus and set appropriate context, depending on your
app you could set a "x11-display" used in GLX or "va-display" if you
already use VA in your application. It's needed on some OpenGL driver
(notably Intel) that do not allow DRI buffers to be shared between
display instance (even if the display is the same).


> 
> And about the GstSurface... are you talking about GstSurfaceBuffer? How this
> arrive to my application?
> If I use an playbin2 pipeline, is it needed to implement a video sink, like
> the ClutterGstVideoSink in order to receive this
> buffer or the vaapisink is able to export them?


Yes, it's GstSurfaceBuffer. You may want to use an appsink to get the
buffers in your application. You'll have to set appropriate template
caps (video/x-surface) otherwise the VA decoder will be skipped.  If
your intention is not to be 100% HW accelerated, you appsink shall also
support at least 1 raw video format. The buffer with caps
"video/x-surface" can be casted to GstSurfaceBuffer.

> 
> And my last one, Are the clutter libraries needed? I would like to minimize
> the amount of libraries on my custom
> system, and I would like to avoid pango, cogl, clutter etc, and let the
> basic ones.

These interfaces has no dependencie, any GL code is implemented in the
VA elements. Finally, have a look at the documentation:
http://cgit.freedesktop.org/gstreamer/gst-plugins-bad/tree/gst-libs/gst/video/videocontext.c?h=0.10
http://cgit.freedesktop.org/gstreamer/gst-plugins-bad/tree/gst-libs/gst/video/gstsurfacebuffer.c?h=0.10
http://cgit.freedesktop.org/gstreamer/gst-plugins-bad/tree/gst-libs/gst/video/gstsurfaceconverter.c?h=0.10

Nicolas
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