<?php
	$ffmpeg = exec('which ffmpeg');
	$ffmpegcmd = $ffmpeg." -i test.mp3 -acodec libvorbis test.ogg";
	echo $ffmpegcmd;
	exec($ffmpegcmd);
?>

This snippets converts a file called 'test.mp3' in the same folder, to a file called 'test.ogg' and saves it in the same folder as well

Convert MP3 to OGG

convert

PHP