ffplay: remove refresh thread to achieve more precise frame delay

We use a refresh loop which displays the frames and also does the polling for
pending events in a non-blocking way. If we know the required delay until the
next frame, then exactly that amount of sleeping will be done. After each
handled event we check if we have to display a frame which kind of makes
displaying the frame a high priority event.

This improves greatly the smoothness of the video output especially with 50fps
content.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: remove remains of video_clock

We are now using a pts based approach, libavutil/libavcodec should provide the
correct pts-es anyway. This also fixes an issue when seeking to a frame with a
pts set to zero.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: only display frames if there are no pending events

Otherwise events could just pile up if displaying a frame takes more time than
the duration of the frame.

Signed-off-by: Marton Balint <cus@passwd.hu>
Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffplay: only display frames if there are no pending events
  ffplay: remove remains of video_clock
  ffplay: remove refresh thread to achieve more precise frame delay

Merged-by: Michael Niedermayer <michaelni@gmx.at>