mhhh... :-/ maybe i'm too naive regarding these coding subjects. i thought that it might only be an question of implementing standard streams somehow. ;-)
i had some success writing a shell script, which calculates aubio-onset-timestamps and filepath of a selected file and saves these into a JSON file, which can be loaded by pressing a button in my hise instrument interface. then i was able to map the corresponding loop ranges to single midi-notes.
Peek 2019-11-26 11-19.gif
but nevertheless, i now found out, that the loop ranges don't work in polyphonic mode, so you can't play 2 different ranges at once. :-/ this is somehow quite unsatisfying, so it seems, that i have to discard my idea of building a loop slicer in hise for the moment.