[Bug 745871] New: wavparse: support for partially unpositioned channels

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=745871

            Bug ID: 745871
           Summary: wavparse: support for partially unpositioned channels
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Mac OS
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-good
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: ilya.konstantinov at gmail.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Here's a sample:

http://www-mmsp.ece.mcgill.ca/documents/AudioFormats/WAVE/Samples/Microsoft/8_Channel_ID.wav

This is a file with 8 channels and the following speaker locations:
FL FR FC LF BL BR - -

(Only 6 allocated, the mask is 0x3f.)

As per spec:
  "Should nChannels exceed the number of bits set in dwChannelMask, then the
remaining channels are not assigned to any particular speaker location. An
audio device would render the remaining channel data to output ports not in
use." [1]

Since GstAudioChannelPositions requires channels to be either all positioned or
all unpositioned, I think we should opt to offer caps of: channels:6,
channel-mask:0x3f. (The remaining 2 channels can be only thrown away.)

Current GStreamer this warning out a few times, since wavparse produces
'channels:8, channel-mask:0x3f':
** (gst-launch-1.0:14286): WARNING **: Invalid channel positions

[1]
https://msdn.microsoft.com/en-us/library/windows/hardware/dn653308(v=vs.85).aspx

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