Thanks very much for that very detailed comment. Comments like this are very helpful. Regarding the images changing at speed, it is always difficult to decide if changing quickly in time with the beat is best or keep them on longer and obviously change less often. Some who also do similar types of videos just show one image on the video throughout the whole video.
The figures from the Youtube stats show no difference to views and watch time for any of the different methods. This makes comments like yours so helpful in deciding what the best method is. Thanks very much and hope you enjoy the music in the future.