Playback jerky and audio interrupted if adjusting audio sync negative

[Peter Bennett]

When playing some HD recordings, adjusting the audio sync lower than -100 causes a jerky playback with audio interruptions and video pauses.

It is exacerbated when playing Live TV.

This is caused by insufficient audio being in the buffer at the time the corresponding video frame is played.

This may be related to #12318

[Peter Bennett]

Attached is a proposed patch. With this patch there is also a setting which can be applied to adjust the amount of audio buffering. "AudioReadAhead" can be set to the number of milliseconds to buffer, so setting for example -O AudioReadAhead=1000 will allow setting a negative audio offset of -1000 milliseconds during playback.

[Peter Bennett]

Proposed fix

[Peter Bennett]

See also #12302 which may be the same problem.

[Peter Bennett <pbennett@…>]

In 7cb7ed9b5e13c1e5d86e22652635f6f7b8f3bc94/mythtv:

Frontend Playback: Add a new setting to address audio stuttering

Replace the "Extra Audio Buffering" checkbox with a millisecond
value. The previous checkbox was a hardcoded 100ms value. If you
are using a negative audio sync adjustment on certain files
you can get audio cutting out unless you increase this value.

Also remove code associated with the "lowbuffers" value that was set
by that checkbox and always use the new setting value.

Fixes #13172