Converting video extensions to flv extension

need to know how to convert video extension after uploading it to server to flv extension using php

and whether my server supports this option, how to know from phpinfo?

There’s no way to convert video formats with built-in PHP functions. You must find a third party software. Try searching and for “plug and play” that you can use with PHP. Do some research on FFMPEG, it’s the best answer but for experienced PHP users who manage servers. Install it on the server and manage it with PHP.

Yes, you need to install the FFMPEG then use exec function from php to convert.