Complex sentence: This is partly due to the work-in-progress nature of experimental filmmaking as films are often reedited (hence the different runtimes), occasionally incorporating reassembled footage of different films, or showed with varying music tracks.
Split into simpler sentences: This is partly due to the work-in-progress nature of experimental filmmaking. Films are often reedited (hence the different runtimes), and occasionally incorporate reassembled footage of different films sometimes to be viewed with varying music tracks.