Image via CrunchBase
- Go to the YouTube page with the video on it.
- [Command] + [Option] + [A] to bring up the Activity window in Safari.
- Under the Address Column find the YouTube page.
- Under that column, look for the largest file size, which will be the video file itself.
- Double click it to download it. Done.
It sounds more cumbersome than it is.
The file will probably download as a .flv file. If you have Perian (a free open source QuickTime component that adds native player support for the most popular video formats) installed on your computer, QuickTime will play the file. Depending on what you want to do with the video file, you may need to recompress it into a different file format. I’ve used Stomp (Mac only) for years. You could also use the (generally) free Zamzar online file conversion utility.