abhishek@abhishek-ThinkPad-R61:~$ youtube-dl -f worst http://www.youtube.com/watch?v=QGhx-u-c5Cg
[youtube] Setting language
WARNING: unable to set language: nonnumeric port: 'port_no'
[youtube] QGhx-u-c5Cg: Downloading video webpage
ERROR: unable to download video webpage: nonnumeric port: 'port_no'
abhishek@abhishek-ThinkPad-R61:~$

sudo add-apt-repository ppa:nilarimogard/webupd8

sudo apt-get update

sudo apt-get install youtube-dl

sudo youtube-dl https://www.youtube.com/watch?v=Ix1rD4JD3eo