I am writing an application where 3650 users upload 3gp video files via e-mail to a web site where they can be watched.

How do I have to proceed to convert the .3gp files into another file format like AVI that is supported by the common media players ?

From "Video in Nokia Phones" I found that 3gp files contain H.263 video and AMR audio. Is it possible to convert the file format without transcoding the video/audio streams?

Are there any tools or API available to do this? Any info or help will be greatly appreciated.