I've used the app to make three videos before, and haven't had any problems up until now.
For my current project, I have a video file, an audio file (.aif) and a midi file.
I've added the video and aif file. The bar along the bottom of the screen says that the video is from 0.00 minutes to 4.27 minutes.
However, when I add the midi file, the video disappears. I still see the image preview of the video, but the bar now says that the video is from 0.00 to 0.00 (ie it's not playing at all)
I hope that makes sense, and I would really appreciate any guidance.