[Live-devel] Behavior of DeviceSource::doGetNextFrame() when no data available

[David Arnold]

What should a DeviceSource, such as a frame grabber, do in doGetNextFrame()
when it determines there is no frame available?  I find no answer in the
FAQ.  The comment in DeviceSource.cpp reads:

// This must be done in a non-blocking fashion - i.e., so that we
// return immediately from this function even if no data is
// currently available.
//

The problem is if I just return, as in:

doGetNextFrame()
{
	if (grabNextFrame() == NO_FRAME_AVAILABLE)
		return;
}

The task scheduler seems to stop.  It appears as though I must invoke
afterGetting(this).  If I must invoke afterGetting() what to I set all the
expected output parameters to (such as fFrameSize, etc) to.

This also raises questions about timing.  doGetNextFrame() runs because the
interval fired.  How do I keep presentation times for the next interval
correct?

In the past, my call to grabNextFrame() blocked in the case where no frame
was available.  When I added an audio stream to the video the blocking call
seems to cause all kinds of timing problems and eventually, VLC and
QuickTime fail to play the stream.

Thank you,

Dave Arnold
Future Concepts

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