On Windows

1. Right-click on the file and select "Properties." The filename should appear at the top, with a three letter extension at the end of it (eg: "hello.mp2").

2. If you see a period and three letters at the end of the file, but there's anything other than ".mp2", then the file is not an MP2. If you don't see any extension, then that means you must change your settings to be able to view extensions.

3. To change your settings so you can see extensions, click the Start menu in the lower left hand corner and select "Control Panel." Double-click "Folder Options" and select the "View" tab. Scroll down until you see "Hide extensions for known file types." The box next to this line should be unchecked. Click "OK" and then repeat steps one and two.

On a Mac

Hold down the "ctrl" key and click on the file, then select "Get Info." Click the grey arrow next to the Section Labeled "Name and Extension." If the file name does not end with ".mp2," it is not an MP2.