I made a program in which you can create a sing-along. Check it out!
That's a clever idea! It's a good use of the microphone.
Its user interface is a little clunky; the user has to time each line manually; that's the sort of chore that computers are good at. I'm envisioning a program in which you just sing the song (or play a song from a file) and you hit some key on the keyboard for each new line. The program would store the value of the timer and reset it. And instead of the user having to tell the program in advance how many llnes are in the song, the program would remember how many times you hit the "next line" key. (A different key would mean "no more lines.")