I have a windows only Direct2D application and would like to implement a video playback system for cutscenes. These files are mp4 but the format can be changed, if need be.
It seems like DirectShow is the advised way to render video/audio on windows.
Now how do I let DirectShow render the video frames to my Direct2D render target?
The VMR-9 filter looks like the best route, but I can't seem to find an elegant way of integrating it into my application
There is no Direct2D/DirectShow interoperability layer in Windows. To fit these two technologies you would have to copy data between the APIs in a rather inefficient way (and this will still take some time to develop the fitting).
With H.264/HEVC MP4 video files you would be better off using Media Foundation to read and decode frames, then load them into Direct2D bitmaps and display in your application. Performance wise it is possible to transfer video frames to Direct2D bitmaps via GPU at reasonable cost and with reasonable development effort, but even if you make a shortcut and do integration roughly and inefficiently it will be on par with DirectShow.
I recommend to start with looking at reading and decoding video frames with Media Foundation Source Reader API. Once you get familiar with fitting the technologies, you will take next step and optimize the transfer by using GPU capacity and interop between Direct3D and Direct2D.