timer: implement AV-sync

This is focused on keeping --on-the-fly-encoding in sync even
over long videos.  The existing code inevitably would fall into a
permanently negative pdata->avd value letting things get
increasingly out of sync and never correcting.

Before removing the vestigial negative avd "don't wait" logic
from get_frame when this permanently negative avd state was
entered, get_frame would just start sampling at an unregulated
fps.

The timer thread which drives get_frame now consults avd on every
tick, Depending on which which half is ahead, the timer will
either cause get_frame to drop frames by advancing the frameno by
more than one, or it will adjust its sleep delay in proportion to
the delta.

See comments in rmd_timer.c for more details.

Note that in testing especially with a loaded system I observed
some surprisingly large deltas where multi-second sleeps occurred
to let the sound catch back up.  I expect to revisit this issue
more in the future, but would just like to get things more
correct for now.

0 files changed, 0 insertions, 0 deletions