I want to change Video's type in website.

For example: avi to 3gpp
rm to 3gpp
3gpp to avi
3gpp to rm...............

My site language used: PHP+MYSQL

What can I do it????????????????????????????

Help.

You have to either find a converter, or you have to learn the structure of all vide file formats you want to convert and write your own. Note that it is going to be processor intensive, so it might not be a good idea to have a web server do such conversions on the fly.