Unfortunately, there's a recursive function call in ao_lavc.c (play
function), leading to a deadlock. The locking is getting a bit messy, so
just make the lock recursive.
This fixes#844.
When writing a video to foo.mp3, the user's intention is clearly to drop
the video stream, and similarly, when writing to foo-%d.png, the
intention is clearly to drop the audio stream. Now, explicit
specification of --no-audio or --no-video is no longer necessary in
these cases.
This re-allows the previous behaviour of being able to reencode with
metadata removed, which is useful when encoding "inconsistently" tagged
data for a device/player that shows file names when tags are not
present.
Since the AO will run in a thread, and there's lots of shared state with
encoding, we have to add locking.
One case this doesn't handle correctly are the encode_lavc_available()
calls in ao_lavc.c and vo_lavc.c. They don't do much (and usually only
to protect against doing --ao=lavc with normal playback), and changing
it would be a bit messy. So just leave them.
This field will be moved out of the ao struct. The encoding code was
basically using an invalid way of accessing this field.
Since the AO will be moved into its own thread too and will do its own
buffering, the AO and the playback core might not even agree which
sample a PTS timestamp belongs to. Add some extrapolation code to handle
this case.
