[Bug 794162] New: gst-python: Can't set channel positions with GstAudio.AudioInfo.set_format

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=794162

            Bug ID: 794162
           Summary: gst-python: Can't set channel positions with
                    GstAudio.AudioInfo.set_format
    Classification: Platform
           Product: GStreamer
           Version: 1.12.4
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-python
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: cl0ne at mithril.org.ua
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Hello, I'm trying to rewrite basic tutorial #8
(https://gstreamer.freedesktop.org/documentation/tutorials/basic/short-cutting-the-pipeline.html)
in Python and in original C code we have lines:

GstAudioInfo info;
gst_audio_info_set_format(&info, GST_AUDIO_FORMAT_S16, SAMPLE_RATE, 1, NULL);

I've rewritten them as:

info = GstAudio.AudioInfo()
info.set_format(
    format=GstAudio.AudioFormat.S16,
    rate=SAMPLE_RATE,
    channels=1,
    position=None
)

According to documentation and source code of `gst_audio_info_set_format` last
parameter `position` is nullable (for 1 and 2 channel setup).
Python documents type of `position` argument as `GstAudio.AudioChannelPosition`
and nothing said if it accepts `None`, so with Python code above I will get an
error: "Argument 4 does not allow None as a value".

I can't pass list of `GstAudio.AudioChannelPosition` instead - I will get
"Expected a GstAudio.AudioChannelPosition, but got list". Isn't list of
`GstAudio.AudioChannelPosition` an equivalent of `GstAudioChannelPosition*`?

Also it's weird why `position` in C code is annotated with `fixed size` of 64
when in fact 64 is the maximum size of channel positions array and channel
count argument used to determine actual array size.

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