https://www.ffmpeg.org/doxygen/trunk/dump_8c_source.html#l00454
- fps =
st->avg_frame_rate
- tbr =
st->r_frame_rate
- tbn =
st->time_base
- tbc =
st->codec->time_base
Average framerate.
- demuxing: May be set by libavformat when creating the stream or in
avformat_find_stream_info()
. - muxing: May be set by the caller before
avformat_write_header()
.