• Philip Langdale's avatar
    matroskadec, matroskadec, srtenc: Read/Write duration for subtitles. · 9d89c8b3
    Philip Langdale authored
    After much discussion and back-and-forth, we reached the conclusion
    that matroska uses convergence_duration for subtitle duration because
    a 32bit value isn't large enough to store the duration if sub-micro-second
    timebases are used. Matroska may not be the only one that supports these
    timebases, but it's certainly the only one that ffmpeg attempts to support
    in this way.
    
    The long term solution that we seemed to reach was that if we encounter
    a matroska file with a sub-micro-second timebase, we should internally
    scale it up to at least micro-second, and then duration can be used
    normally. This suggests that on the encode side, we should not allow
    generation of files with sub-micro-second timebases, but that's a separate
    issue.
    
    That being a non-trivial change, and the subtitle interoperability breakage
    being very real, I'm re-submitting this small change for consideration.
    
    In this diff, we make sure that duration is populated by the matroska
    demuxer, and that convergence_duration is respected in matroskaenc and
    srtenc, but that duration is used otherwise. This ends up being a strict
    improvement - pipelines that use convergence duration are unchanged, and
    ones that are currently broken due to the duration mismatch will start
    working - except for the ones with the extreme timebases, but those were
    already broken.
    Signed-off-by: 's avatarPhilip Langdale <philipl@overt.org>
    9d89c8b3
matroskadec.c 85.5 KB