This is great, Mark! This is easily the most useable browser-based transcription interface I've come across. One thing that would be useful, I think, is having the more traditional start/stop/auto-backstep buttons, which would be best accomplished with key bindings.
My vague, non-technical impression is that key bindings can sometimes be challenging in-browser. However, if there's any way to do it with the "\" (start) and "]" (stop and step back a specified number of milliseconds) keys, I think that could be relatively easy and ergonomic for the user. (for this user, anyway!) Backstep ms range should probably be 500-2500.
I think the inactivity detection and chunk size functionality is great, too, though, and could hopefully coexist with the hotkeys.
Do you prefer to have this feedback on GGroups or GH?
Best,
Zev