[mythtv] Android mediacodec woes

[Peter Bennett]

The double framerate that I am getting from mediacodec is proving to be 
a rather complicated problem to solve. With the situation the way it is 
now, the display of elapsed time is wrong and jumps are very wrong. For 
example after watching for 5 minutes, the OSD shows 10 minutes, and 
doing a forward jump of 1 minute jumps to the real 11 minutes, i.e. 
jumps forward 6 minutes instead of jumping forward 1 minute. Jumping 
back a minute  actually jumps forward 4 minutes.

Detecting the condition is easy enough. Fixing it, not so easy.

I first thought that I could simply double the fps value stored in 
AVFormatDecoder and MythPlayer. That does not work. I found that the 
MpegPreProcess is resetting it back to 29.97 on the next frame. Why do 
we parse the Mpeg input? Maybe that should be eliminated. We could get 
framerate from the decoded timestamps.

I then realized that the whole approach of changing the fps is flawed 
because the code uses framecount all over the place for calculating 
positions in the file. If the frame count from the demultiplexer 
(avformat) is half the frame count from the decoder, all sorts of 
calculations go wrong.

There is a feature in MythPlayer for m_double_framerate for double 
framerate deinterlacers. I am now thinking I should extend that to 
support this new situation of double framerate interlacer that is built 
into the decoder. It will need a number of changes, currently 
m_double_framerate is disabled as soon as it sees a non-deinterlaced 
frame. Currently m_double_framerate indicator causes the same frame to 
be passed to the video output twice, now it will need two consecutive 
frames passed to the video output.

Another option is just drop every second frame. This would be easiest 
but that will surely reduce the quality, which is not what we want.

Peter