Takes a Vimeo or YouTube URL and returns the iframe embed URL. Other URLs remain untouched.

func.get_video_embed_url.php

function get_video_embed_url($url) {
    // Check for YouTube
    $matchFound = preg_match('/^(https?:\/\/(www\.)?youtube\.com\/watch\?(t=(.+)&)?v=|https?:\/\/youtu\.be\/)([^?]+)(\?(t=(.+))?.*)?$/', $url, $matches);
    if ($matchFound) {
        // Video is a Youtube video
        $url = '//www.youtube.com/embed/' . $matches[5];
        if ($matches[4]) {
            $url = $url . '?start=' . $matches[4];
        } else if ($matches[8]) {
            $url = $url . '?start=' . $matches[8];
        }
    } else {
        // Check for Vimeo
        $matchFound = preg_match('#^https?://vimeo\.com/([a-zA-Z0-9]+)/?$#', $url, $matches);
        if ($matchFound) {
            // Video is a Vimeo video
            $url = '//player.vimeo.com/video/' . $matches[1] . '?byline=0&portrait=0';
        }
    }
    return $url;
}