Pitch-shift or time-stretch the instrumental

Queues a transposed or tempo-adjusted copy of the instrumental, which is what makes it usable as a backing track in a different key. Renders are free, they cost only storage. Applies to the instrumental, never the original.

If that exact render already exists the response is ready with an empty job_id and nothing is queued. Otherwise it is queued: poll GET /songs/{id}/renders with the same parameters until it returns a URL. Requires status: "ready", and at least one of semitones/speed must differ from the default.