The following guide their implementation in linux mint, with other distros, you do the same.

First you install youtube-dl command:

sudo apt-get install youtube-dl

Once installed, to download video from youtube you perform the following steps:
1. In the video you want to download page
2. Copy video link from the navigation bar of the browser
3. Open a terminal and execute the command:

youtube-dl link

And the video will be downloaded in your home directory

But you download videos may have incorrect format you wish. To know and dowload the format you want, execute the following command, it lists the corresponding code format.

youtube-dl -F link

From this we know the code (code) of video formats (CEO 5 flv format [240*400]). Perform the following command to download the format you want:

youtube-dl -f  code link

Well done, home directory and open video! ^^

Reference Articles in: http://community.linuxmint.com