adjacent_image_link

 *
 * This implements the functionality of the Video Shortcode for displaying
 * WordPress mp4s in a post.
 *
 * @since 3.6.0
 *
 * @global int $content_width
 *
 * @param array  $attr {
 *     Attributes of the shortcode.
 *
 *     @type string $src      URL to the source of the video file. Default empty.
 *     @type int    $height   Height of the video embed in pixels. Default 360.
 *     @type int    $width    Width of the video embed in pixels. Default $content_width or 640.
 *     @type string $poster   The 'poster' attribute for the `<video>` element. Default empty.
 *     @type string $loop     The 'loop' attribute for the `<video>` element. Default empty.
 *     @type string $autoplay The 'autoplay' attribute for the `<video>` element. Default empty.
 *     @type string $preload  The 'preload' attribute for the `<video>` element.
 *                            Default 'metadata'.
 *     @type string $class    The 'class' attribute for the `<video>` element.
 *                            Default 'wp-video-shortcode'.
 * }
 * @param string $content Shortcode content.
 * @return string|void HTML content to display video.
 */
function wp_video_shortcode( $attr, $content = '' ) {
	global $content_width;
	$post_id = get_post() ? get_the_ID() : 0;

	static $instance = 0;
	$instance++;

	/**
	 * Filters the default video shortcode output.
	 *
	 * If the filtered output isn't empty, it will be used instead of generating
	 * the default video template.
	 *
	 * @since 3.6.0
	 *
	 * @see wp_video_shortcode()
	 *
	 * @param string $html     Empty variable to be replaced with shortcode markup.
	 * @param array  $attr     Attributes of the shortcode. @see wp_video_shortcode()
	 * @param string $content  Video shortcode content.
	 * @param int    $instance Unique numeric ID of this video shortcode instance.
	 */
	$override = apply_filters( 'wp_video_shortcode_override', '', $attr, $content, $instance );

	if ( '' !== $override ) {