make it better

backend/app.js

@@ -758,9 +758,9 @@ app.post('/downloadFile', async (req, res) => {
     let file = null;
     if (!is_playlist) {
         if (type === 'audio') {
-            file = __dirname + '/' + 'audio/' + fileNames + '.mp3';
+            file = __dirname + '/' + audioFolderPath + fileNames + '.mp3';
         } else if (type === 'video') {
-            file = __dirname + '/' + 'video/' + fileNames + '.mp4';
+            file = __dirname + '/' + videoFolderPath + fileNames + '.mp4';
         }
     } else {
         file = await createPlaylistZipFile(fileNames, type, outputName);

db.json

@@ -0,0 +1,6 @@
+{
+  "playlists": {
+    "audio": [],
+    "video": []
+  }
+}

package.json

@@ -4,13 +4,13 @@
   "license": "MIT",
   "scripts": {
     "ng": "ng",
-    "start": "node backend/app.js",
+    "start": "cd backend && node app.js",
     "build": "ng build",
     "test": "ng test",
     "lint": "ng lint",
     "e2e": "ng e2e",
     "electron": "ng build --base-href ./ && electron .",
-    "postinstall": "ng build --prod && mkdir dist/backend && mkdir dist/backend/config && mkdir dist/backend/audio && mkdir dist/backend/video && cp src/assets/default.json dist/backend/config/default.json && cp backend/app.js dist/backend/app.js && cp backend/package.json dist/backend/package.json && npm --prefix dist/backend install dist/backend"
+    "postinstall": "ng build --prod && mkdir dist/backend && mkdir dist/backend/config && mkdir dist/backend/audio && mkdir dist/backend/video && cp src/assets/default.json dist/backend/config/default.json && cp backend/app.js dist/backend/app.js && cp backend/package.json dist/backend/package.json && cd dist/backend && npm install"
   },
   "private": true,
   "dependencies": {