Comment by georgel

It's been around and available as an API to devs since at least 2021 in iOS. The problem was even on the best iPhone at that time, I could never get it past ~0.8x speed and after 15-20 minutes the device would heat up so much the display dimmed.

For context, I was working on a podcast app with on-device transcription, had to park that idea for years before it got to today's performance.