File types: use metadata information.

@jankeromnes, this should make the sounds rock-solid!

Walk-through of my analysis:

1. Sound files were eventually modified and no longer playable.
2. By looking at the binary, a great deal of `EF BF BD` were added here and there, which is the signature of incorrectly read UTF8 values.
3. It turns out that the file types defaulted to text files at some point.
4. Also, audio files didn't have their own type information anywhere, which means they were sure to hit the default.
5. Finally, types didn't use metadata information, which was a shame.