If you are using a Mac and are looking for an application to download videos from YouTube, then look no further. The application you need is MacTubes. The first thing you do is download MacTubes and install on your Mac.
Connect to YouTube and play the video of your choice
Copy the URL in the address bar
Click the menu "File> Open Video"
Paste the URL of the video and click "OK"
The video will be streamed in the program's interface, click on the gear-shaped button located on the lower left corner and select "Download" and choose the format in which you want to download the video: FLV, MP4, HD, HD1080.