I thought apps were for phones.

I transcribe interesting traditional music as sheet music, usually from a performance on YouTube. It would be nice to be told right away what the key and time signature are.

Come to think of it, the video is quite uninformative. How does it listen? i.e, what do I plug it into? What do I need to own to operate it?

Can it listen to a YouTube video and tell me what key and time the music is in? Must it be an mp3? or what?