I’ve got the reference 
This is a product idea that we’ve been discussing internally since at least 2008, if not earlier.
The more time passes, the less it comes up. It would be a nice feature for phonograph and terrestrial radio users. I’m not sure whether it would work well synced up with a screen, because all of that transmission, conversion, and re-transmission is going to add latency, some of which might be difficult to model.
RAAT is capable of supporting use cases like this. Of course, we would need to build the “input device” piece. This isn’t in the schedule right now because we have a lot of other priorities stacked up right now, but I would love to see it happen someday.