With Biab it generates up the track into RAM then plays from there,
BBW4 (Biab) will do the same for the Plugin then writes it to a wav file.
If I drop a wav/wma from my RealTracks folder into Reaper, slice it up, change the pitch, stretch and rearrange it, (Non Destructive Editing)
when I play it back it will still be playing the same original untouched source wav file.
Couldn't you get the Plugin to do the same ?
Rather than all the time waiting for it to be generated to wav files,
it should be way quicker to generate up just the reference data and play direct from the wav/wma source files.
Then the time would be just in the render to wav when you finally get what you need, rather than all the render time for something that may not be right, not to mention all the SavedTracks hard drive space.
That's why with the Vol/Pan and more audio sends it can be all done in the Plugin without using any hard drive space or long render times.
I know if I generate a track in Reaper with a script pulling the needed sections out of a wav file to fit the chord track it's instant,
it's only simple random matching where as Biab will do more musical calculations but it should be near as quick, it would have to be as quick as generating midi.
So moving just the necessary generate code from BBW4 into the BiabVST code would give you instant play.
It's like if I freeze all the tracks in Biab and save to SGU it will store all the reference data for the tracks: file, bar/s, time start/time end, transpose and stretch amount.
So if I open this SGU in the BiabVST it should be able to read and play those section direct from file without generating into RAM then rendering to wav.
See pic below Reaper is just pulling out sections of wav that match the chord track, it will just play direct from the source until I render it.
Then this is the render time in the next pic, it will render all those sections to a new wav on your hard drive.