(http://askwiki.blogspot.com/2006/10/convert-all-videosaudio-files-to.html) But it seems they too have competition now.. hmm competitions is always good. The new kid on the block is ZamZar.com.
ZamZar, offers free online file conversion and allows users to upload and convert the files upto 100 Mbs in one go, and it sends you the link of the file for download on your specified email address. It currently supports 5 image formats, 14 document formats, 11 video and 9 audio formats. The files are kept on the servers of Zamzar for 24 hrs. the service is worth tring. In the past users only option was using the softwares to do the convertion task and most of them used by sharewares and the worst thing was that they were specific to certain formats and were specific to Images, documents, videos etc., that is, a software could only convert either video files from one format to other or could only deal with images and similary only with sound. Now all this online converters are really cool .