fixed the issue of not returning the default provided value when finding binary path

lib/Controller/YoutubeController.php

@@ -81,7 +81,7 @@ class YoutubeController extends Controller
         $yt = $this->youtube;
         $yt->audioOnly = (bool) $this->request->getParam('audio-only');
         if (!$yt->isInstalled()) {
-            return new JSONResponse(["error" => "Youtube-dl is not installed!"]);
+            return new JSONResponse(["error" => "Please install the latest youtube-dl or make the bundled binary file executable in ncdownloader/bin"]);
         }
         if (Helper::isGetUrlSite($url)) {
             return new JSONResponse($this->downloadUrlSite($url));

lib/Tools/Helper.php

@@ -201,7 +201,7 @@ class Helper
         }
         $dataPath = \OC::$server->getSystemConfig()->getValue('datadirectory');
         $paths = ['/usr/local/sbin', '/usr/local/bin', '/usr/sbin', '/usr/bin', '/sbin', '/bin', '/opt/bin', $dataPath . "/bin"];
-        $result = null;
+        $result = $default;
         $exeSniffer = new ExecutableFinder();
         // Returns null if nothing is found
         $result = $exeSniffer->find($program, $default, $paths);

lib/Tools/Youtube.php

@@ -60,7 +60,7 @@ class Youtube
         if (Helper::ffmpegInstalled()) {
             $this->addOption('--prefer-ffmpeg');
             $this->addOption('--add-metadata');
-            $this->setOption('--metadata-from-title',"%(artist)s-%(title)s");
+            $this->setOption('--metadata-from-title', "%(artist)s-%(title)s");
             $this->addOption('--extract-audio');
         }
         $this->outTpl = "/%(id)s-%(title)s.m4a";