remove av_frame_get_best_effort_timestamp

[markreidvfx]

I don't think we can rely on av_frame_get_best_effort_timestamp to get the frame pts, if we have to be compatibility with libav. I seems only ffmpeg has it.

I have this http://dranger.com/ffmpeg/tutorial05.html implemented in one of my branches, I'll try bringing it back.

[mikeboers]

As far as I can tell, the best_effort_timestamp is set to the return value from guess_correct_pts.

See definition and usage of guess_correct_pts.

[markreidvfx]

ah I see. guess_correct_pts was originally in cmdutil.c libav

ffmpeg promoted it into avcodec, avlib has not. commit moving it

[mikeboers]

This discussion transitioned to #35 a while ago.