If you're experiencing issues with the preview video/live visualizer giving you a black screen, you may need to go into your config.json file with a text editor (directory is listed at the top of the player's window) and make sure none of the indices you're using for your midi tracks are null. If they are, assign them a value. save your changes, then try opening ALMAMPlayer again.
For example, I had 5 midi channels, but despite that all the values under parallax were listed as null. Assigning everything I was using a value fixed the visualizer and preview video.