You are right, so these videos were very good for me, and I know how to do it with the techniques shown.
What I was hoping for, was to be able to edit the playback length with automation envelopes. Instead of me triggering or editing midi/samples.
I wanted to make an nice non-linear (exponential) curve of the playback time or even an S-type easily. From full length to minimum back to full.
Another question is I guess is can you automation write, playback time?
Does that make sense?