You may want to attempt the transition using BIAB's Song Form Medley Maker. It's designed to transition songs with different keys, tempo's or styles. Transitions can be any number of bars between 0-16 and BIAB will automatically create the transition and input transition chords. The user can override the chords and change them to whatever is wanted.

I loaded two demo songs, one at 128 and the other at 256 with a two bar transition and BIAB had no difficulty creating a 4 bar drum fill going from 128 BPM to 256 BPM. (Four bars derived from 2 bar transition for song one and 2 bar transition for song two.)

Charlie

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Medley Maker.jpg (111.53 KB, 103 downloads)
Screenshot 2022-06-08 173710.jpg (451.1 KB, 105 downloads)

BIAB 2025:RB 2025, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.