[Bug 723327] New: matroskademux: Set buffer offsets for output

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=723327
  GStreamer | gst-plugins-good | git

           Summary: matroskademux: Set buffer offsets for output
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-good
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: self at brendanlong.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


I'm looking at using the buffer offset as a unique identifier for
caption/subtitle cues. This HTML mailing list thread is relevant:

http://lists.w3.org/Archives/Public/public-html/2014Jan/0083.html

Specifically:

> Is the UA expected to keep a unique internal id for each in-band
> TextTrackCue it creates so that it doesn't reinsert a cue that
> was inserted previously, but was modified?

To which the answer appears to be, "yes".

The worst-case scenario for this seems to be WebVTT, where the *only* way to
uniquely identify cues is by where they appear in a file:

    00:00:00 --> 00:00:05
    Lorem ipsum

    00:00:00 --> 00:00:05
    Lorem ipsum

So, I'd like to use GST_BUFFER_OFFSET, but it looks like it never sets set for
any caption or subtitle formats. As a proof-of-concept, I'd like to implement
this for Matroska/SSA, since it seems to be the best-supported cue format right
now. Does that make sense?

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