Have you ever needed to download a video off of Youtube to your machine to view locally later? Forget those online free youtube download sites or apps. The most efficient way is to use a free app called jdownloader which is available for Windows, Mac, Linux and, as a Java applet. Download from: http://jdownloader.org/download/index
Download, install and run this, and then find the youtube video you need. Copy the URL of the video, and jdownloader’s linkgrabber should find it.
It’ll take a few seconds and will then present you with a few resolution and format options. Choose mp4 when in doubt (2nd option in the JPEG below) and the largest size you need. Then choose Continue with selected downloads and voila! the file will download to your machine.