[Bug 739968] New: v4l2src outputs bogus DTS

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=739968
  GStreamer | gst-plugins-good | git

           Summary: v4l2src outputs bogus DTS
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-good
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: thaytan at noraisin.net
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


v4l2src doesn't explicitly set any DTS on outgoing buffers, which means
basesrc sets a default DTS (0, or segment start). There's no way to prevent
basesrc from that behaviour at the moment, which means that all v4l2src streams
start with a buffer where DTS = 0.

For encoded formats, that means that (for example) h264parse starts producing
a stream withmonotonically increasing DTS from 0, and some arbitrarily offset
PTS time range - leading to strange muxing.

For raw video, v4l2src can just set DTS = PTS on the output stream, but that
won't work for encoded formats with frame reordering, and I'm not sure what
v4l2src should do - or if we should change basesrc to not set that first DTS.

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