[mythtv] FFmpeg sync

[Anduin Withers]

I don't see how the AC3 decoder can be correct when handling error 
states. FFmpeg [13397] 
(http://svn.mplayerhq.hu/ffmpeg/trunk/libavcodec/ac3dec.c?r1=13385&r2=13397) 
changed from any error for the frame being fatal to only sync errors 
being so.

This same change disables audio block decoding when an error occurred 
and removes frame skipping on block decode failure (data_size set to 
zero, frame size returned).

What this can mean currently (this being the error that made me look at it):

- AC3 CRC is bad.
- Audio blocks are not decoded.
- Data that happens to be there (no decoding has been done, not even a 
failed one) is dutifully copied as if the decoding occurred.
- What may have been an imperceptible interruption in audio is now annoying.

-- 
Anduin Withers