[Bug 783470] New: qtmux with x264 causes offset in video timestamps

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=783470

            Bug ID: 783470
           Summary: qtmux with x264 causes offset in video timestamps
    Classification: Platform
           Product: GStreamer
           Version: 1.12.0
                OS: Linux
            Status: NEW
          Severity: minor
          Priority: Normal
         Component: gst-plugins-good
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: jpa at gnobug.mail.kapsi.fi
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

I'm generating a file like this:

gst-launch-1.0 -v videotestsrc num-buffers=10 ! identity silent=false ! x264enc
! qtmux ! filesink location="tmp.mp4" | grep -o "pts: *[^ ]*"
pts: 0:00:00.000000000,
pts: 0:00:00.033333333,
...

and decoding it by:

gst-launch-1.0 -v filesrc location="tmp.mp4" ! qtdemux ! avdec_h264 ! fakesink
silent=false | grep -o "pts: *[^ ]*"
pts: 0:00:00.066666666,
pts: 0:00:00.100000000,
...

The PTS of the first frame appears to change for some reason, always by two
frame durations. This causes offset in lipsync if the file has audio in it.

I haven't git bisected yet, but the bug is present in 1.12.0 and 1.8.3. In
1.3.3 the output begins at 0 as expected. Files generated in 1.3.3 however show
the offset when decoded in newer versions, and files generated in newer
versions show the offset also in 1.3.3. Muxing raw video (without x264enc)
gives correct timestamps in all versions.

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