Funny that you mention it, a few months ago when updating stuff I got a new feature on my Android phone... Offline subtitle generation based on audio, just realtime generated from anything outputing sound on my phone.

A Google search suggests this might be an older feature - not sure if my phone didn't support it, or if I maybe just missed it, or if they added a more obvious button.

Google has a separate app for that stuff, called Private Compute Services. Right now it's nothing like an offline Google assistant replacement, but I thought it's really nice to have that stuff available without relying on internet access.