Get youtube video id from url.

youtube-video-id.php

<?php

/**
 * Determine the video ID from the URL.
 *
 * @param string $url URL.
 *
 * @return int|false Video ID, or false if none could be retrieved.
 */
function get_video_id_from_url( $url ) {
	$parsed_url = wp_parse_url( $url );

	if ( ! isset( $parsed_url['host'] ) ) {
		return false;
	}

	$domain = implode( '.', array_slice( explode( '.', $parsed_url['host'] ), -2 ) );
	if ( ! in_array( $domain, [ 'youtu.be', 'youtube.com', 'youtube-nocookie.com' ], true ) ) {
		return false;
	}

	if ( ! isset( $parsed_url['path'] ) ) {
		return false;
	}

	$segments = explode( '/', trim( $parsed_url['path'], '/' ) );

	$query_vars = [];
	if ( isset( $parsed_url['query'] ) ) {
		wp_parse_str( $parsed_url['query'], $query_vars );

		// Handle video ID in v query param, e.g. <https://www.youtube.com/watch?v=XOY3ZUO6P0k>.
		// Support is also included for other query params which don't appear to be supported by YouTube anymore.
		if ( isset( $query_vars['v'] ) ) {
			return $query_vars['v'];
		} elseif ( isset( $query_vars['vi'] ) ) {
			return $query_vars['vi'];
		}
	}

	if ( empty( $segments[0] ) ) {
		return false;
	}

	// For shortened URLs like <http://youtu.be/XOY3ZUO6P0k>, the slug is the first path segment.
	if ( 'youtu.be' === $parsed_url['host'] ) {
		return $segments[0];
	}

	// For non-shortened URLs, the video ID is in the second path segment. For example:
	// * https://www.youtube.com/watch/XOY3ZUO6P0k
	// * https://www.youtube.com/embed/XOY3ZUO6P0k
	// Other top-level segments indicate non-video URLs. There are examples of URLs having segments including
	// 'v', 'vi', and 'e' but these do not work anymore. In any case, they are added here for completeness.
	if ( ! empty( $segments[1] ) && in_array( $segments[0], [ 'embed', 'watch', 'v', 'vi', 'e' ], true ) ) {
		return $segments[1];
	}

	return false;
}