Mirror Booth Setup
In Sparkbooth 6 or higher, there is a mirror booth mode to use with your mirror booth hardware.
How to add your own videos to Sparkbooth's mirror booth mode
If your custom mp4 videos are not playing, it could be due to the mp4 encoding. You can fix this by re-encoding the videos using H.264. The Adobe CC Encoder is a media encoder that can re-encode videos.