[Bug 741306] New: qtmux: handle overlapping subtitle buffers properly

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=741306
  GStreamer | gst-plugins-good | git

           Summary: qtmux: handle overlapping subtitle buffers properly
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-good
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: matej.knopp at gmail.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Overlapping subtitle buffers (buffers that start before previous buffer ends)
are legal in many containers (i.e. MKV), but can not be represented in MP4.
Trying to remux such file currently results in invalid file, because timestamp
delta between buffer end time and next buffer start time is negative

In order to handle this well, the muxer should split and combine buffers in a
way so that no information is lost. I.e. Two overlapping input buffers should
be muxed as three separate buffers, with second buffer combining content from
both input buffers.

[=======Buffer In 1========]
               [=======Buffer In 2========]

 [Buffer Out 1][Buffer Out 2][Buffer Out 3]

Sample MKV file with overlapped subtitles
https://s3.amazonaws.com/MatejK/Samples/OverlappedSubtitles.mkv

Remuxed file without the patch
https://s3.amazonaws.com/MatejK/Samples/OverlappedSubtitlesWithoutPatch.mp4

Remuxed file with the patch
https://s3.amazonaws.com/MatejK/Samples/OverlappedSubtitlesWithPatch.mp4

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