Oh, I’m afraid there is no good support for playing media with Matinee yet. The problem is that the media API currently relies on the timing of the video decoder for playback, but Matinee will try to render the frames as quickly as possible. What you would need is a way for Matinee (or the UWorld in general) to tell the media which frame it needs to show.
Unfortunately, this is not possible right now. It was an oversight in the initial draft of the Media design, because we needed something up and running quickly for in-game playback. It will be addressed in the future, but Media is currently on hold until we get other higher priority tasks out of the way.
Sorry that I don’t have better news for you.
As a workaround, you could maybe try to play the Matinee as a regular game play session, so that it plays at 1.0x real-time speed, and record that output to a video.