[libav-bugs] [Bug 488] New: use blackdetect to position keyframes

bugzilla-daemon at aruru.libav.org bugzilla-daemon at aruru.libav.org
Sun Apr 7 08:56:34 CEST 2013


           Summary: use blackdetect to position keyframes
           Product: Libav
           Version: 9
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: Normal
         Component: libavfilter
        AssignedTo: bugzilla at libav.org
        ReportedBy: jon77h at gmail.com

Depends on implementing blackdetect; see bug 442.

blackdetect would be most useful if, during transcoding, it could force a
keyframe at the start and end of each black sequence.

I guess many people (as i do) cut ads from DVB recordings, with apps such as
avidemux and MPEG Streamclip, which can cut only on keyframes.

Some (if not all) channels fade to black briefly at the start and end of each
ad break.

Often I transcode first, so i can delete the big mpeg2 TS file sooner, and do
the cutting later.

x264's scenecut detection tends to put a keyframe near the edge of a
fade-out/in, which is not usually the best place to cut.

If blackdetect could be used to put a keyframe or three within each sequence of
black frames, it would really help.

(hmmm ... what if you could detect silence at the same time, and put the
keyframes where there is both black and silence? ;)

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