Yeah it does seem technically within reach and potentially solvable. I was thinking of including song identification when I mentioned an NN as a potential solution. I’m also assuming that there a bunch of other serious complications like resampling and clock skew between the two streams, a changing frequency response over time, etc. You can imagine that if there are audio dropouts or song pauses in the video you’re trying to fix, then naively subtracting the source song will result in accidentally playing the copyrighted song instead of removing it. And it might be trickier if people sing along to the song, etc. I think this situation is quite a bit tougher than the standard trick people use to remove ambient audio by recording with a 2nd mic further away and subtracting it.