Hi
You can convert multiple video files (or a single file) between formats with "AnyVideo Converter"
http://www.any-video-converter.com/products/for_video_free/
It's free and easy to use. Just drag and drop the videos to convert into the left hand pane and set up the type of file you want to convert them to from the list on the right. There are multiple defaults available but you can choose the output type/frame rate/size/and codec etc if you click the specific box listed on the right and then the down arrow to select your option.
Files are converted one after the other with a visible progress bar for each and the output is placed in a program created folder on the desktop. The original files are not altered.
Hope this helps
Nat