[FFmpeg-devel] [PATCH] libavformat: libavformat: output cues for each subtitle block in MKV muxer

John Peebles johnpeeb at gmail.com
Sun May 25 17:00:21 CEST 2014


> Are you sure this is how it's supposed to work?
The proposal for adding the CueDuration and CueRelativePosition
elements indicates that this is the correct behavior. It says:

> With the proposed
> change a muxer could include all subtitle blocks and their duration in
> the cues and a splitter would have all the information required to
> display the subtitles directly after seeking.

See http://lists.matroska.org/pipermail/matro
ska-devel/2012-September/004249.html
for the full email thread.


On Sun, May 25, 2014 at 10:28 AM, wm4 <nfxjfg at googlemail.com> wrote:

> On Sun, 25 May 2014 10:05:24 -0400
> John Peebles <johnpeeb at gmail.com> wrote:
>
> > > This patch doesn't apply on FFmpeg git master.
> > The new version attached should apply.
> >
> > > please do not include re-indent change into the patch
> > done
> >
> > > Can you also provide a sample and command line to reproduce?
> > Sure.
> > (1) Download the attached same-time-script.mkv file. Note that while
> > this file only contains a subtitle track in order to keep the file size
> > down,
> > the bug still happens even if there are other tracks.
> > (2) Run ffmpeg -i same-time-script.ass -c copy -map 0 bad.mkv
> > (3) Inspect the ebml data in bad.mkv. Notice that while there are two
> > subtitle blocks (one for each of two different subtitles), there is only
> a
> > CueTrackPositions element for the first block. There should be one for
> > each block.
> >
> > > Is the issue you are fixing the same as ticket #3149?
> > No, this patch only deals with cues for subtitle tracks, not audio
> tracks.
> >
>
> Are you sure this is how it's supposed to work? The sample file you
> posted has two cue entries for the same time. I think it should have
> only 1 entry, pointing to the first packet. Is it documented somewhere
> how this should work? (I know it's not in the "specification".) The
> fact that your sample was apparently produced by mkvmerge doesn't say
> much; redundant cues are probably ok, but the question is whether
> they're "needed".
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