According to the tests in 23b72ad, when we are reading a compressed stream, the type returned by `stream_props_GetMediaType()` should reflect compressed format even if we finnally output uncomressed data. For example, if we use wmvcore reader to read a WMV3 stream and output RGB24, the format information returned by `stream_props_GetMediaType()` should be WMV3, not RGB24.
-- v8: winegstreamer: Use codec format in stream_props_GetMediaType.