public function _validate_header_video( $validity, $value ) {
		$video = get_attached_file( absint( $value ) );
		if ( $video ) {
			$size = filesize( $video );
			if ( $size > 8 * MB_IN_BYTES ) {
				$validity->add(
					'size_too_large',
					__( 'This video file is too large to use as a header video. Try a shorter video or optimize the compression settings and re-upload a file that is less than 8MB. Or, upload your video to YouTube and link it with the option below.' )
				);
			}
			if ( '.mp4' !== substr( $video, -4 ) && '.mov' !== substr( $video, -4 ) ) { // Check for .mp4 or .mov format, which (assuming h.264 encoding) are the only cross-browser-supported formats.
				$validity->add(
					'invalid_file_type',
					sprintf(
						/* translators: 1: .mp4, 2: .mov */
						__( 'Only %1$s or %2$s files may be used for header video. Please convert your video file and try again, or, upload your video to YouTube and link it with the option below.' ),
						'<code>.mp4</code>',
						'<code>.mov</code>'
					)
				);
			}
		}
		return $validity;
	}