The function fetches response headers from YouTube's oEmbed URL for a given video and crawls through thenm in order to find whether the video actually exists.

check-youtube-video-oembed.php

<?php

/**
 * Find if a Youtube video exists. 
 *
 * The function fetches response headers from YouTube's oEmbed URL for a given video
 * and crawls through thenm in order to find whether the video actually exists.
 * 
 * @link https://imelgrat.me/json-xml/oembed-protocol-embed-videos-news/
 * 
 * @param string   $videoID      The YouTube video ID to check for
 * 
 * @return bool Returns true if the video exists or false if the video can't be found.
 */
function YouTube_Check_ID($videoID)
{
    $is_valid = true;

		// YouTube oEmbed API endpoint (https://www.youtube.com/oembed)
		// Query it using the video's URL as parameter
		// The "format" parameter may be either JSON or XML. Not relevant for this tes.

    $theURL = "http://www.youtube.com/oembed?url=http://www.youtube.com/watch?v=$videoID&amp;format=json";

    $file_headers = @get_headers($url);
    if ($file_headers === false) {
        $is_valid = false; // when server not found
    } else {
        foreach ($file_headers as $header) {
				// Parse all headers. Corrects $url when 301/302 redirect(s) lead(s) to 200:
            if (preg_match("/^Location: (http.+)$/", $header, $m)) {
                $url = $m[1];
            }

				// Use regex to detect HTTP response codes 
            if (preg_match("/^HTTP.+\s(\d\d\d)\s/", $header, $m)) {
                $code = $m[1];
            }
        }

			// $code 404 This must be a bad video ID.
        if ($code == 404) //
        {
            $is_valid = false;
        }
    }

    return $is_valid;
}

$id = 'BKorP55Aqvg'; //Video id goes here

if (YouTube_Check_ID($id)) {
    echo "Yes! The video exists";
} else {
    echo "Oh, no! The video code is wrong and it can't be found on YouTube";
}

?>