fftools/ffmpeg: stop using OutputStream.frame_number for streamcopy

This field is currently used by checks
- skipping packets before the first keyframe
- skipping packets before start time
to test whether any packets have been output already. But since
frame_number is incremented after the bitstream filters are applied
(which may involve delay), this use is incorrect. The keyframe check
works around this by adding an extra flag, the start-time check does
not.

Simplify both checks by replacing the seen_kf flag with a flag tracking
whether any packets have been output by do_streamcopy().

0 files changed, 0 insertions, 0 deletions