WP_Widget_Media_Audio::get_instance_schema()

	public function get_instance_schema() {
		$schema = array_merge(
			parent::get_instance_schema(),
			array(
				'preload' => array(
					'type' => 'string',
					'enum' => array( 'none', 'auto', 'metadata' ),
					'default' => 'none',
					'description' => __( 'Preload' ),
				),
				'loop' => array(
					'type' => 'boolean',
					'default' => false,
					'description' => __( 'Loop' ),
				),
			)
		);

		foreach ( wp_get_audio_extensions() as $audio_extension ) {
			$schema[ $audio_extension ] = array(
				'type' => 'string',
				'default' => '',
				'format' => 'uri',
				/* translators: %s: audio extension */
				'description' => sprintf( __( 'URL to the %s audio source file' ), $audio_extension ),
			);
		}

		return $schema;
	}