wp_get_video_extensions()

function wp_get_video_extensions() {
	/**
	 * Filters the list of supported video formats.
	 *
	 * @since WP-3.6.0
	 *
	 * @param array $extensions An array of support video formats. Defaults are
	 *                          'mp4', 'm4v', 'webm', 'ogv', 'flv'.
	 */
	return apply_filters( 'wp_video_extensions', array( 'mp4', 'm4v', 'webm', 'ogv', 'flv' ) );
}