Simple PHP Function to extract YouTube Video ID from several different types of YouTube links.

get-ytid.php

function extractYouTubeID($url) {
    $pattern = '%(?:youtube(?:-nocookie)?\.com/(?:[^/]+/.+/|(?:v|e(?:mbed)?)|embed/|v/|.*[?&]v=)|youtu\.be/)([^"&?/ ]{11})%i';
    preg_match($pattern, $url, $matches);
    return $matches[1] ?? null;
}

/*
Here is a quick test of all supported YouTube URL types.
$urls = [
    'https://www.youtube.com/watch?v=dQw4w9WgXcQ',
    'https://youtu.be/dQw4w9WgXcQ',
    'https://www.youtube.com/embed/dQw4w9WgXcQ',
    'https://www.youtube.com/v/dQw4w9WgXcQ?version=3&autohide=1',
    'https://www.youtube.com/watch?v=dQw4w9WgXcQ&feature=youtu.be',
    'https://m.youtube.com/watch?v=dQw4w9WgXcQ',
    'https://www.youtube.com/user/username#p/a/u/1/dQw4w9WgXcQ',
    'https://www.youtube.com/watch?feature=player_embedded&v=dQw4w9WgXcQ'
];

echo '<pre>';
foreach ($urls as $url) {
    echo 'URL: ' . $url . ' -> Video ID: ' . extractYouTubeID($url) . "\n";
}
echo '</pre>';
*/