Thanks Pete, it took me ages how to do a video with a track.

With iMovie on the iPad, you load the recorded Sax music track in first then you load in a recorded video file. Then you detach the video file’s sound track and delete it, so you’re just left with the video and the Sax music track.

Make sure the video file is longer than the Sax music, then just trim off the end of the video file to be the same length as the Sax music.
Save the final stuff to iCloud and upload to vimeo or youtube.

The only problem now, is i’ll have do some separate video recordings.