I started over today. I wanted to see if I could beat my time.
Well, I'm up to 19-3 again, and so far the movie is 123 frames ahead of the submitted one!
In game, I measure improvement by "steps". A step is 8 frames. It takes 8 frames to perform just about any action- step from one square to another, collect a diamond one square away from you, push a bug, etc...
19-1: Gained 1 step on this level. Apparently, pushing the rock onto the bug and waiting for the rock below to fall in order to collect the diamond is faster than dropping the rock on the bug and running over to collect the diamond. This is the fastest this level can be completed. Further improvement is impossible.
19-2: No improvement. I performed this level identcally to the previous level- further improvement is impossible.
19-3: I ganed a freaking 12 steps on this level!! That's 96 frames! I did this by rethinking my strategy. Collecting the 2 diamonds on top at the beginning is faster than waiting for later to run all the way over there and pick them up. Also, getting to the bottom left diamond by running under everything is faster than entering from the top, waiting for all the rocks to topple to let you through. Further improvement may still be possible.
So 13 steps, combined with faster menus and password entry, imrpoved this video by 123 frames so far.
http://www.samus.co.uk/cad/boulder_dash/bd_q4_2.fcm
http://www.samus.co.uk/cad/boulder_dash/run_progress.txt
I'll update those files as I complete this run.