Enqueue FitVids.JS in WordPress.

functions.php

<?php

/**
 * Enqueue scripts
 */
function prefix_enqueue_scripts() {
	$uri = get_template_directory_uri();

	$suffix = defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min';

	// FitVids - http://fitvidsjs.com/
	wp_register_script(
		'fitvids',
		$uri . "/assets/fitvids/jquery.fitvids$suffix.js",
		array( 'jquery' ),
		'1.1.0',
		true
	);

	// Theme
	wp_enqueue_script(
		'theme',
		$uri . "/js/script$suffix.js",
		array( 'jquery', 'fitvids' ),
		'1.0.0',
		true
	);
}

add_action( 'wp_enqueue_scripts', 'prefix_enqueue_scripts' );