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.
Turns out the pitch was accidentally used as width, leading to an out of bounds read/write.
I kept the pitch in the struct for completeness' sake. It may be needed later, if only for error checks.