According to the official ffmpeg-php website: ffmpeg-php is an extension for PHP that adds an easy to use, object-oriented API for accessing and retrieving information from video and audio files. It has methods for returning frames from movie files as images that can be manipulated using PHP’s image functions
Inodder to use this extension;you [...]

ffmpeg is a popular audio/video encoder and decoder . If you are planning to roll out a website that does video conversion like the popular youtube this document is for you . Now if you allow your users to upload content shot using mobile phones inoder to decode the same you may need AMR codec [...]