Sometimes when I am editing video, I find it necessary to convert some video or audio files from one format to another. I recently came across this free tool that will convert almost any media file from one format to another. It can handle all these different file formats.
MP4/3GP/MPG/AVI/WMV/FLV/SWF
MP3/WMA/AMR/OGG/AAC/WAV
JPG/BMP/PNG/TIF/ICO/GIF/TGA
And it does a pretty good job too. Check it out here
http://www.formatoz.com/