This usually happens because the publisher doesn't have the right to distribute the video in your country so they apply YouTube regional restrictions/country restrictions.
For example: https://www.youtube.com/watch?v=kirSofzvXN0 is available in US, but not in India.
The easiest way to get around this is to replace
youtube in the url with
youpak. The rest of the link remains exactly same.
This does not work for all videos all the time (obviously can't expect a small company to have the means of Google). http://www.youpak.com/watch?v=dQw4w9WgXcQ isn't working for me at the time of writing this, but it has worked for me most times in the past.