How to use SourceReader (for H.264 to RGB conversion)?

I'm trying to move from DirectShow land to Media Foundation and an trying to build around some existing code. Unfortunately I've run in some issues.

Basically what I want to do is take an MPEG4 video that is encoded in H.264 and be able to convert it to RGB or YUV. I can then take that raw YUV or RGB data so that I can make an OpenGL texture.

I've concluded that I need to use the SourceReader and have the IMFSourceReader::ReadSample method set up and returning samples. The problem is that I can't seem to be able to set the subtype to be MEDIASUBTYPE_UYVY or _RGB24 like I could in DirectShow.
Basically I get an MF_E_INVALIDMEDIATYPE error when I do IMFSourceReader::SetCurrentMediaType with my media type (of which I've only set MF_MT_MAJOR_TYPE and MF_MT_SUBTYPE)

Reading http://msdn.microsoft.com/en-us/library/dd797815%28VS.85%29.aspx gives me the impression that I can't even use those subtypes anyway. If that is the case, then is is possible to convert the H.264 to RGB?

Which leads me to my next question. Basically all I want is raw RGB (24bit) data so that I can create an OpenGL texture. Would I be best to:
- follow the instructions at the end of http://msdn.microsoft.com/en-us/library/dd389281%28VS.85%29.aspx#why_use_source_reader and set up the DirectX components then...
- ultimately receive IDirect3DSurface9 objects of which I can call GetDC on it and retrieve the raw RGB data which I can then pass to my OpenGL texture.

Is this even possible? I'm getting a little lost amongst all the documentation at the moment and just want to try and cut down what to focus on.

Thanks

- Edit
It occurred to me that trying to get OpenGL and DirectX to share the graphics card is not a good idea. Instead I'll just get the H.264 to output to MEDIASUBTYPE_YUY2 and convert it to RGB with an OpenGL shader (or something).

Am I right in thinking that MediaFoundation is still limited in video support i.e. it doesn't support MP4v?