This is happening to me too... with 8 platforms... startup.mp4 from the download section of the forums. . black screen.
Okay, so I kind of narrowed it down. When I get the black intro screen, I can closed out Big Box mode and go to videos directory and double-click and play startup.mp4 with VLC. I close that and the next time I run Big Box Mode, the video plays correctly (no black screen), but when I close Big Box and try to open Big Box again, black screen intro. Reopening the video temp fixes it for one startup. Maybe this can help you pinpoint this issue with a patch/fix? Hope this helps.