Cannot add some YouTube videos to offline mode I'm trying to add videos to offline mode, but it added only one video successfully. For any other videos I try, it says,


  Offline Unavailable. Sorry, this video can't be taken offline.


What should I do?
There is nothing you can do, since it seems not all videos can be taken offline. From an article on Techniqued,

Note: Remember not all videos can be taken offline and some videos might show this error &quot;Sorry, this video can’t be taken offline&quot; message. YouTube does not clearly mention what is the criteria for videos to be available offline. So in case you encounter this issue, you will not be able to view the video offline.

Based on research, there is a possibility that videos with copyrighted content (e.g. Vevo) can't be taken offline. A commenter wrote,

Most of the videos I tried, are giving error, ‘This video can’t be taken offline.’
Most of them are from vevo, however I tried for an old hindi song and that one worked.

Or, it might be related to YouTube Music Key.

Availability
You must be a Music Key subscriber to take music videos offline.

Other than that, there's almost no clue.