[larrymcg]

sng, mid and rmi files are all forms of midi files which do not contain any audio.
wav, mp3 and mp4 files contain audio.
There really isn't a good way to convert audio to midi unless the audio is very simple -- something like a single instrument playing one note at a time. It's just too complex of a problem to analyze the audio and figure out what kind of instruments are being used and what notes they are playing at any instant in time.