Add 'MKV' and 'MP4' to supported WPMovieLibrary media types

functions.php

<?php

/**
 * Add new movie medias
 * 
 * @param    array    Exisiting media
 * 
 * @return   array    Updated media
 */
function wpmoly_add_new_media_type( $media ) {

	$new_media = array(
		'mkv' => 'MKV',
		'mp4' => 'MP4'
	);

	$media = array_merge( $media, $new_media );

	return $media;
}
add_filter( 'wpmoly_filter_detail_media', 'wpmoly_add_new_media_type', 10, 1 );