Use separate locks for audio and video
Fix audio mutex usage in cellRec.
Removes can_consume_sample, since we don't do any processing
between can_consume_sample and present_samples.
Use get_system_time for consistency.
Move pts reset to set_video_sink.
Make start time atomic.
Remove frame and sample counts.
Use m_active to early out to reduce mutex locks.
Do not try to present samples if the recording mode is stopped anyway.