Upmix all stems in a stem group into a spatial .wav file
Call order
- Initiate Spatial Upmix: start processing the stem group into a spatial upmix.
- Get Spatial Upmix Status: fetch the status of the upmix, and find out when the results are ready.
- Get Spatial Upmix Results: fetch the results of the upmix (when the upmix status is done).