[PATCH 2/3] winegstreamer: Use decodebin to initialize media streams.

[Derek Lesho]

> Well, for that matter, you don't exactly need to use
> gst_app_sink_pull_preroll(); gst_app_sink_pull_sample() also blocks. But
> I'm led to believe that mfplat requires you to know the caps before you
> start queuing samples.
>
Well, as of right now, our pipeline is fully setup in the stream-added 
callback for decodebin, so it's not like once we know our caps, we have 
to modify the pipeline elements.  Also, this is completely transparent 
to media foundation, pulling from the preroll queue will not affect the 
main queue.  Of course, in the case where media source user decides to 
use a different type (which pretty much means using videoconvert or 
audioconvert), we just update the appsink "caps" property and the caps 
are renegotiated.