Books.
Opening books or videos, What is your preference?
The problem with books is that they tend to require selective reading. Often, much of the material is just there for reference - possibly useful for consultation after a game. One video problem can be coping with the speed of presentation. Also, videos are often not well suited for reference-consultation after a game.

Books are light years better than videos.
Videos lead to what is called passive learning and are ineffective in the long run.
Using books PROPERLY would require you to get out a board and pieces (NOT your artificial intelligence) and play thru the positions on a 3D board, stopping to think about what you would play next at each position, especially diagram positions as those usually indicate a critical moment. Play through all side notes as well. If this requires you to play through the first 17 moves a dozen times, so be it. It will drill the opening moves into your mind, and you should have figured out the reason for move 9 back at move 9. Now that you are at move 18 after having gone through variation B4b2d of Black's 17th move, there should be no reason to restudy move 9. You should know it by then.
So long story short, books and not videos, board and pieces and not a 2-D board on a computer screen.
"... I feel that the main reasons to buy an opening book are to give a good overview of the opening, and to explain general plans and ideas. ..." - GM John Nunn (2006)
"... If the book contains illustrative games, it is worth playing these over first ..." - GM John Nunn (2006)
"... the average player only needs to know a limited amount about the openings he plays. Providing he understands the main aims of the opening, a few typical plans and a handful of basic variations, that is enough. ..." - FM Steve Giddins (2008)
"... Everyman Chess has started a new series aimed at those who want to understand the basics of an opening, i.e., the not-yet-so-strong players. ... I imagine [there] will be a long series based on the premise of bringing the basic ideas of an opening to the reader through plenty of introductory text, game annotations, hints, plans and much more. ..." - FM Carsten Hansen (2002)
https://web.archive.org/web/20140627055734/http://www.chesscafe.com/text/hansen38.pdf
"The way I suggest you study this book is to play through the main games once, relatively quickly, and then start playing the variation in actual games. Playing an opening in real games is of vital importance - without this kind of live practice it is impossible to get a 'feel' for the kind of game it leads to. There is time enough later for involvement with the details, after playing your games it is good to look up the line." - GM Nigel Davies (2005)
http://theweekinchess.com/john-watson-reviews/chessbase-training-dvds-and-downloads
http://theweekinchess.com/john-watson-reviews/chessbase-dvds-and-downloads-part-2
I am currently debating whether using opening books or videos would be more effective for building my opening repertoire. Regardless, I am inputting the variations and comments about the plans for each opening in chess opening wizard. I was curious to see what you guys prefer for the easiest and most efficient workflow.