Dear Maintainer, The problem was solved on Bullseye by changing Aegisub's audio player to PulseAudio in View > Options > Advanced > Audio > Audio Player. The default was ALSA. This also worked on Ubuntu 18.04 and 20.04
Hope this helps.
- Bug#968835: aegisub: Audio plays at incomprehensible speed Dave
- Bug#968835: Resolved: Changed Audio Player to PulseAudio Ren
