You can use the following ways to download youtube without an internet connection:
An extension in Firefox called Keep the Tube, is now also compatible with the Chrome browser, Internet Explorer, and so forth. It is more interesting than Keep Keep Tube Tube is not only to work with YouTube, but could also for CollegeHumor, Facebook, Google Video, Metacafe and other video sharing sites.
When you see the video that you like, just click on the icon Keep Tube Firefoc or in part in his bookmarks. From there, you’ll see on the page Keep the Tube where you can download the video in one or more formats and file size. It would be better if the download in MP4 format and use the highest resolution.