Visit YouTube page from Google chrome browser.
Right Click on page and select Inspect Element. This will open Chrome Developers Tool.
Go to the Emulate tab shown on bottom of the Developers Tool Window.
Select any Device and click on Emulate.
Refresh your page, now you will see YouTube in mobile view (if not the enter http://m.youtube.com/ and hit enter).
Search and select video you want to download and then click on video to play this will open new tab with black screen playing video.
Now right click on the video (black screen) and select “Save Video as”, that’s it you have done….