Record RTSP stream with FFmpeg libavformat

Question

I\'m trying to record RTSP stream from Axis camera with FFmpeg libavformat. I can grab video from files and then save it to another file, this is OK. But camera sends strang

Answer 1

In my experience with a modern H.264 encoder, I'm finding that the duration returned by ffmpeg is only a "suggestion" and that there is some "jitter" in the PTS. The only accurate way to determine frame rate or duration is to measure it yourself using the PTS values.

For an H.264 encoder running at 30fps, duration is always reported as 3000/90000, while measured duration is usually +/- 1 but periodically jumps say 3000+25 one frame and 3000-25 the next. I'm smoothing this out for recording by noticing any adjacent frames with opposite deviation and adjusting the PTS of the 2nd frame while preserving the total duration.

This give me a stream with an occasional (calculated) duration of 30001 or 2999, reflecting clock drift.

When recording a 29.97fps stream, av_read_frame() always returns a duration of 3000, while the nominal calculated duration is 3003 (correct for 29.97) with the same jitter and drift as described above.

In my case, I just built a state machine to clean up the timing. Hoping this helps someone.