Here's one I came up with from combining info from other answers here and elsewhere:
function validId($id) {
return preg_match('/^[a-zA-Z0-9_-]{11}$/', $id) > 0;
}
function isvalYtube($url) {
$purl = str_ireplace('www.', '', parse_url($url, PHP_URL_HOST));
if (!strpos($url, 'youtu.be/') && ($purl != 'youtu.be')) {
if (strpos($url, 'watch') && ($purl = 'youtube.com')) {
parse_str(parse_url($url, PHP_URL_QUERY), $id);
if (!empty($id['v'])) { return(validId($id['v']) ? true : false); } else { return false; }
}
} else {
if (!empty(basename($url))) { return(validId(basename($url)) ? true : false); } else { return false; }
}
}
echo isvalYtube($url) ? 'valid link' : 'invalid link';
First function checks if we're dealing with a valid Youtube video ID.
Second function simply checks if it's a valid youtube VIDEO LINK or VIDEO from PLAYLIST LINK, excluding channel links.
Note: It doesn't determine if it's an active video nor does it check if it exists or not. These functions act merely as Youtube video-link syntax checkers and should be treated as such.
Usage examples:
$url = 'http://www.youtube.com/watch?v=o_QBk4VwnIA';
echo isvalYtube($url) ? 'valid link' : 'invalid link';
//returns 'valid link'
$url = 'http://youtu.be/o_QBk4VwnIA';
echo isvalYtube($url) ? 'valid link' : 'invalid link';
//returns 'valid link'
$url = 'http://www.youtube.com/watch?v=o_QBk4VwnIA&feature=youtu.be';
echo isvalYtube($url) ? 'valid link' : 'invalid link';
//returns 'valid link'
$url = 'https://www.youtube.com/watch?v=Sq3eLdixvCc&list=OLAK5uy_nvaYLo9AG_rZyqkXzYlkJfLjBuZS84bIU';
echo isvalYtube($url) ? 'valid link' : 'invalid link';
//returns 'valid link'
$url = 'https://www.youtube.com/channel/UCMPQY9gW0hQ9e_-IdQUKEAw';
echo isvalYtube($url) ? 'valid link' : 'invalid link';
//returns 'invalid link'