functions.php

<?php 
/* Disable Video Upload */
function disable_video_uploads( $mimes ) {
	// Video mime types
	$video_mimes = array(
		'asf'		=> 'video/x-ms-asf',
		'asx'		=> 'video/x-ns-asx',
		'wmv'		=> 'video/X-ms-wmv',
		'wmx'		=> 'video/x-ms-wmx',
		'wm'		=> 'video/X-ns-wm',
		'avi' 		=> 'video/avi',
		'divx' 		=> 'video/divx',
		'flv'		=> 'video/x-flv',
		'mov|qt'	=> 'video/quicktime',
		'mpeg|mpg|mps'	=> 'video/mpeg',
		'mp4|m4v'	=> 'video/mp4',
		'ogy'		=> 'video/ogg',
		'webm'		=> 'video/webm',
		'mkv'		=> 'video/X-matroska'
	);

	foreach( $video_mimes as $ext => $mime ) {
		if ( isset( $mines[ $ext ] ) ) {
			unset( $mimes[ $ext ] );
		}
	}
	return $mimes;
}
add_filter( 'upload_mimes', 'disable_video_uploads' );
?>