[Bug 749930] New: Libav / FFMPEG does not report interlaced content correctly.

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=749930

            Bug ID: 749930
           Summary: Libav / FFMPEG does not report interlaced content
                    correctly.
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: All
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: don't know
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: frederic.turmel at arris.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

FFMPEG decoder such as mpeg2dec and libav decoder avdec_h264 does not report
interlaced content correctly. This problem could exist in other decoder when
producing interlaced output.

Currently the Gstreamer implementation report GST_VIDEO_INTERLACE_MODE_MIXED
To the best of my knowledge, I believe this is wrong as FFMPEG/LIBAV produce
Interlace Interleaved frame. 1 frame contains both top and bottom field.

This came to light while testing the new decklink video sink.

I replaced the GST_VIDEO_INTERLACE_MODE_MIXED flag in gstavviddec.c for
avdec_h264 and gstmpeg2dec.c for mpeg2 decoder.

After the modification i was able to output video at 1080i59.94 without issues.

Before the change, the following line as an example did not work since
decklinksink is expecting interlace-interleaved source:

gst-launch-1.0 -v --gst-debug-level=3 udpsrc uri="udp://239.127.23.2:5724"
buffer-size=5000000 ! queue ! tsdemux ! h264parse ! queue ! avdec_h264 ! queue
! videoconvert ! queue ! videorate ! queue ! decklinkvideosink mode=12

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