[Bug 792589] New: msdk: decode: Add VC1 decoder

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=792589

            Bug ID: 792589
           Summary: msdk: decode: Add VC1 decoder
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: Normal
         Component: gst-plugins-bad
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: bsreerenj at gmail.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Enable VC1 decoder in MSDK plugin.

VC1 enablement is not straightforward like other codecs because of the input
stream formats supported by MediaSDK.

* Simple & Main profile (WMV3)

We can enable Simple and Main profile decode with the usage of vc1parse in the
pipeline. MSDK expecting in-stream sequence layer (SMPTE 421M Annex L, Table
265) for simple and main profile.

The decodebin/playbin won't work because: 
1: most of the asf streams output codec-data with 4 bytes sequence header
(Table SMPTE 421M Annex L 263)
2: vc1parse is not yet an autoplugging element in the pipeline.
3: we don't have format conversion support in msdkvc1dec yet.

* Advanced Profile (WVC1)

Adding support for WVC1 requires more changes in msdk base decoder because:
The current implementation of msdk base decoder expecting a full frame at the
input, which mandates a parser before the decoder in many cases(eg: avc decoder
only supports "byte-stream+au"). So there is no global mfxBitstream tacking (no
support for bitstream appending to the same mfxBitstream) is enabled.

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