[mythtv] Trying to debug seek problems

[David Abrahams]

It's pretty common, when I hit the 'E' key while watching a recording,
for the indicator to end up at zero.  Likewise it's common for me to
end up back at the beginning of all video when I use the skip
forward/reverse keys.

It seems the culprit is lurking in the PrepareFrame member function of
most of the classes derived from VideoOutput.  For example, here's the
one from VideoOutputQuartz:

  void VideoOutputQuartz::PrepareFrame(VideoFrame *buffer, FrameScanType t)
  {
      (void)t;

      if (!buffer)
          buffer = vbuffers.GetScratchFrame();

      framesPlayed = buffer->frameNumber + 1;
  }


When paused, the buffer argument to PrepareFrame is 0 (NULL) and the
result of calling VideoBuffers::GetScratchFrame is always a buffer
whose frameNumber is zero.  I believe there's some kind of race
condition when pausing, so sometimes this doesn't cause a problem.
However, when I change this to


  void VideoOutputQuartz::PrepareFrame(VideoFrame *buffer, FrameScanType t)
  {
      (void)t;

      if (buffer)
            framesPlayed = buffer->frameNumber + 1;
  }

everything works perfectly.

As I said, this bug is apparently repeated through most of the
subclasses of VideoOutput, the exceptions being VideoOutputIvtv and
VideoOutputXv.  I suppose most people are using Xv and that's why it
hasn't been more widely reported.  Regardless, the repetition of this
code pattern strongly suggests that some refactoring is in order.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com