the music is more distracting at higher speeds for me and i usually listen at 1.5x when walking or at the gym. you could have the music be a separate audio track where the playback speed doesnt impact it and the toggle plays it simultaneously with the vocal track or not.
The issue is that the voice track will be shorter than the music track if you speed it up. So you'll have the music playing until the end, but the voice track ending before that. It's definitely possible, just a bit more complex to implement.
Maybe when I have the feature to mute the music, I can just mute the music when the speed is changed?
