then what is the direct way to download youtube video thank you in advance
First install the script youtube-dl
mentioned earlier in the thread; on Ubuntu the command is
sudo apt-get install youtube-dl
You can then use youtube-dl to download the clip associated with a given youtube URL, e.g.:
The output file is a flash video, and should be playable with e.g. mplayer and vlc, or you can convert it to other formats using ffmpeg or mencoder.