Update: Check out the latest post on this subject here:
You may have seen one of my previous posts, Batch Downloading and Converting Youtube Videos.
It was a great method that has stopped working only within the past few months. The reason being = DASH.
Dash is a streaming protocol that has made it difficult to download entire videos with the old methods out there. Trust me I tried them all in a 2 day panic before a show and only found 1 downloader that worked properly with the Dash Protocol. (I read about FFMPEG w/ JDownloader working, but only on windows and some macs)
The best so far, CYS Downloader: http://www.cys-audiovideodownloader.com/ works perfectly with the Firefox web browser. I would lay out how-to’s, but it is a very simple process and all the necessary instructions are on the website.
Hope that helps, leave any comments or questions you may have.