[FFmpeg-user] Meaning of duration

[Jarno Suni]

Suppose you have recorded an Opus stream with -copyts. Then

ffprobe -v error -show_entries format=start_time,duration -- recording.opus

shows non-zero start_time and possibly huge duration that does not
reflect to the file size. I think you get the actual duration of the
recording by subtracting start_time from the given duration. Is that
intentional and by definition?

I tried recording some MP3 streams with and without -copyts, and
start_time is then always small non-zero number (0.011995). Why is
that? I have not tried all formats, but apparently they vary in this
respect.