or you can add effects in real time.
Kanto Karaoke plays .midi, .kar and .mp3 files as it records your voice using the microphone. It's very easy to use the app. You just have to click on 'Open file' and select the track that you want to sing. It will immediately appear on the screen and the music will play as it shows the song's lyrics.
In addition, this karaoke app includes a feature that converts MIDI files to MP3s, though the free version of Kanto Karaoke will stop after the first minute.