Get a YouTube video ID from any format of YouTube URL.

youtube-id-from-url.php

<?php

function youtube_id_from_url( $url = null ) {

	if ( ! $url || ( stripos( $url, 'youtube.com' ) === false && stripos( $url, 'youtu.be' ) === false ) ) {
		return false;
	}

	$parsed_url = parse_url( $url );

	if ( stripos( $url, '?v=' ) !== false ) {
		parse_str( $parsed_url['query'] );
		$id = $v;
	} else {
		$id = end( explode( '/', $parsed_url['path'] ) );
	}

	return $id;

}