[FFmpeg-user] Meaning of duration

Ferdi Scholten ferdi at sttc-nlp.nl
Fri Dec 30 18:54:01 EET 2022

> 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.
Try using this together with -copyts


    When used with copyts, shift input timestamps so they start at zero.

    This means that using e.g. |-ss 50| will make output timestamps
    start at 50 seconds, regardless of what timestamp the input file
    started at.

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