function get_youtube_video_id($video_id)
{

    // Did we get a URL?
    if ( FALSE !== filter_var( $video_id, FILTER_VALIDATE_URL ) )
    {

        // http://www.youtube.com/v/abcxyz123
        if ( FALSE !== strpos( $video_id, '/v/' ) )
        {
            list( , $video_id ) = explode( '/v/', $video_id );
        }

        // http://www.youtube.com/watch?v=abcxyz123
        else
        {
            $video_query = parse_url( $video_id, PHP_URL_QUERY );
            parse_str( $video_query, $video_params );
            $video_id = $video_params['v'];
        }

    }

    return $video_id;

}

$link = "http://www.youtube.com/watch?v=oHg5SJYRHA0";
$video_id = explode("?v=", $link);
$video_id = $video_id[1];

$link = "http://www.youtube.com/watch?v=oHg5SJYRHA0&lololo";
$video_id = explode("?v=", $link); // For videos like http://www.youtube.com/watch?v=...
if (empty($video_id[1]))
    $video_id = explode("/v/", $link); // For videos like http://www.youtube.com/watch/v/..

$video_id = explode("&", $video_id[1]); // Deleting any other params
$video_id = $video_id[0];

(?v=|/v/)([-a-zA-Z0-9]+)

function youtubeID($url){
     $res = explode("v",$url);
     if(isset($res[1])) {
        $res1 = explode('&',$res[1]);
        if(isset($res1[1])){
            $res[1] = $res1[0];
        }
        $res1 = explode('#',$res[1]);
        if(isset($res1[1])){
            $res[1] = $res1[0];
        }
     }
     return substr($res[1],1,12);
     return false;
 }
$url = "http://www.youtube.com/watch/v/y40ND8kXDlg";
echo youtubeID($url1);

$parts = explode('=', $link);

// $parts[1] will y40ND8kXDlg

preg_match("#([wd-]){11}#is", 'http://www.youtube.com/watch?v=y40ND8kXDlg', $matches);
echo $matches[1];

$link = 'http://www.youtube.com/watch?v=oHg5SJYRHA0&player=normal';

  strtok($link, '?');

  parse_str(strtok(''));

  echo $v;

Function getYouTubeID($URL){
    $YouTubeCheck = preg_match('![?&]{1}v=([^&]+)!', $URL . '&', $Data);
    If($YouTubeCheck){
        $VideoID = $Data[1];
    }
    Return $VideoID;
}

If(preg_match('![?&]{1}v=([^&]+)!', $URL . '&', $Data)){
        $VideoID = $Data[1];
}

function getID_youtube($url)
{
    parse_str(parse_url($url, PHP_URL_QUERY), $ID_youtube);
    return $ID_youtube['v'];
}