FFMpeg hls_time accuracy

Question

I'm using ffmpeg library in an ios application to convert mp4 video to HLS. I want to keep the ts file duration as exactly 10 seconds. So I put the following code.

av_opt_set_int(formatContext->priv_data, "hls_time", 10, AV_OPT_SEARCH_CHILDREN);

But the result is not exactly 10 seconds, the duration falls around 10 second, say 11 seconds, 12 seconds, 9 seconds etc. Is there any method to get the accurate 10 second segments from the ffmpeg?

Answer 1

Every HLS packet must start with a keyframe, and the placement of those keyframes seems to be variable in your source.

FFmpeg will do its best to cut the file into 10s packets, but if at some point there is 12s between 2 keyframes, the segment will be 12s.

Apart from reencoding the source and set a constant keyframe interval, there isn't much you can do.