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

[Atlant Schmidt]

Josiah:

  Thanks! Tips and tricks are always appreciated!

                   Atlant

-----Original Message-----
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Josiah Bryan
Sent: Monday, September 20, 2010 16:12
To: 'Qt Interest'
Subject: [Qt-interest] HOWTO: Grab Video from QMediaPlayer - Solution in Search of a Problem

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

--

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

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