[Qt-interest] HOWTO: Grab Video from QMediaPlayer - Solution in Search of a Problem

[Josiah Bryan]

This is just a 'solution' email - no question, no problem - just an 
email in case someone else is trying to figure this out, hopefully this 
may save someone some time.

I've managed to cobble together a Qt example (don't remember which one) 
and some advice on various bulletin boards in order to create a class 
that can grab video from QMediaPlayer (from the QtMobility Solution) 
without having to render the video on screen first.

Basically, it creates a 'fake' QAbstractVideoSurface - that's easy 
enough to do - one of the Qt examples (maybe in the QtMobility examples) 
shows you basically how to create a video surface. The magic was the 
line someone showed me, basically like this:

QVideoRendererControl* rendererControl = 
m_player->service()->requestControl<QVideoRendererControl*>();

if (rendererControl)
     rendererControl->setSurface(m_surfaceAdapter);

Basically, it attaches the fake video surface (m_surfaceAdapter) to the 
output of the QMediaPlayer object - and voila! We've got video streaming 
into our video surface for us to do whatever we want with it. In my 
case, I convert each from to a QImage and render into an OpenGL texture 
for compositing with various other elements on screen.

(See http://code.google.com/p/dviz/, specifically the latest post on 
that page about SVN r664 for an example of the compositing.)

I don't claim to have invented anything new here - just showing a 
concrete example of how to put the various bits and pieces together 
inorder to achieve the desired result. Note that QMediaPlayer still 
handles all the audio paths - I just take the video frames.

(I'm sure if you go digging through *how* I use the video, the 
GLDrawable setup, and all the rest of the framework behind LiveMix, 
you'll find plenty to criticize or tell me how I can do it better - if 
you see anything you want to tell me about, feel free to. Or not. This 
is more about the video adapter, not really about how unimaginative of a 
coder I am. Thanks for your patience! :-)

Cheers!
-Josiah Bryan

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-=-=-=-=-=-=-=-=-=-=-=-=-
Josiah Bryan
Productive Concepts, Inc.
jbryan at pciint.com
(765) 964-6009, ext. 224