livechat.php

<?php

try {
    if (count(["cid"]) == 0) {
         $channelId = "UCL7oxb4N7uxEOHPlhFFxAhg";
    }else{
         $channelId = ["cid"];
    }
    $videoId = getLiveVideoID($channelId);
    $chatUrl = "https://www.youtube.com/live_chat?v=" . trim($videoId) . "?is_popout=1"
?>
<script type="text/javascript">
    window.location = "<?php echo $chatUrl; ?>"
</script>
<br>
The live chat URL is <?php echo $chatUrl; ?>
<?php
} catch(Exception $e) {
    // Echo the generated error
    echo "ERROR: " . $e->getMessage();
}

// The method which finds the video ID
function getLiveVideoID($channelId)
{
    $videoId = null;

    // Fetch the livestream page
    if($data = file_get_contents('https://www.youtube.com/embed/live_stream?channel='.$channelId))
    {
        // Find the video ID in there
        if(preg_match('/\'VIDEO_ID\': \"(.*?)\"/', $data, $matches))
            $videoId = $matches[1];
        else
            throw new Exception('Could not find video ID');
    }
    else
        throw new Exception('Could not fetch data');

    return $videoId;
}