If you are trying to download the YouTube videos and convert that to audio here’s the solution. AVDownloader is the perfect solution for that. AVDownloader lets you download videos from Google Video or Youtube and view them later, even without internet connection.
The application is simple to use, by using the internal browser, navigate to a web page containing a video from Google Video or YouTube (including the official sites) and select it. At that point, the application will ask you if you just want to see the video or download it. Selecting the second option (Use This Video), it will start the download.
All downloaded videos will be included in the special section, where you can create playlists and also select a video to extract only the audio part and save it in a song listenable via iPhone.
AVDOwnloader is now offered on the App Store at a price of 1.59 € .