koel/app/Providers/YouTubeServiceProvider.php

<?php

namespace App\Providers;

use App\Services\YouTube;
use Illuminate\Support\ServiceProvider;

class YouTubeServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap the application services.
     *
     * @return void
     */
    public function boot()
    {
        //
    }

    /**
     * Register the application services.
     *
     * @return void
     */
    public function register()
    {
        app()->singleton('YouTube', function () {
            return new YouTube();
        });
    }
}