This patch doesn't work now. Zebediah, I think I need your help.
My goal is to get the original stream format in `stream_props_GetMediaType()`. For example, if I use wmreader to open a WMV3 stream, then this function should return WMV3 format as its result.
I expect preferred_format to hold the format I need. But test shows that preferred_format is always RGB24 even if I open a WMV stream. I found that preferred_format is written in `wg_parser.c: sink_event_cb(): case GST_EVENT_CAPS`. So it means that the caps here is "video/x-raw", not "video/x-wmv" as I expected.
So how could I get the stream format I want when I open a compressed stream using wmreader?