I'm not sure if offloading sound to a seperate worker would be possible for something like JSMESS -- most emulators I've looked at are single-threaded save for

I'm not sure if offloading sound to a seperate worker would be possible for something like JSMESS -- most emulators I've looked at are single-threaded save for rendering operations in certain safe cases, and sound generation is often inexorably linked with the CPU loop. Maybe running the entire emulator on a worker would help (assuming it's GC-free)? But now you've got potential issues with input and video latency.