There are two problems with non-briefing videos, which the attached map can help show. These are seen in 2.09 and 2.10 dev.

1) A video will only play once. To see this, start the FM, walk to the brass button and frob it. You will see a 5-second video (with audio skipped).
When it's done, rehighlight & refrob the brass button. This time, there will be only a black screen for 5 seconds.

Even if you do a Quicksave before the first play, and then a Quickload afterwards, the second attempt will not show the video again. This is actually the main use case, where you are trying to do a replay.

2) To do audio, it is possible to extract it from the .mp4 file and play it back as one or more separate audio files, with one or more appropriate sys.waits. (I've done that in the FM away0.) For simplicity, this is not shown in the example map. If it were, you would hear the audio sync'd with video on the first button press, and the audio alone on the second button press.

But it would be great if you didn't have to do that extraction. Regrettably, the technique given in wiki entry "Cutscene video with FFmpeg", to use the audio from an mpeg video, does not seem to work for a non-briefing video. The audio does not play. To attempt this with the attached map, make these changes:

a) In materials/cutscene_video.mtr, add "withAudio" following the "videoMap" keyword

b) Add a sound shader sound/cutscene_video.sndshd with content:

video/cutscene_video
{
   fromVideo video/cutscene_video // .mtr
}