this solves the oft-recurring problem where we assign
a beat-count of '3' or '7' because minipm mis-detected the tempo,
and that situation is vanishingly rare. it's better to assume 4 or 8
the user always has the option to change the number of beats (and
therefore the detected tempo) manually, for those clips that are
in a different time signature. but minibpm cannot be expected
to help us there.
NOTE: this is a fallback to make things 'just work' lacking any other context.
* if the tempo is detected in the filename, we use that instead
* clips that were recorded to the timeline use that bpm+timesig
* in the future we can use file-metadata (acidized wave?) instead
* this is audio-only: midi files can have an embedded timesignature
but... given no other information, experience says the vast majority
of downloaded/purchased clips will be 1,2 or 4 bars at 4/4.
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