Advantages and Disadvantages of learning mathematics and physics subjects through lecture videos
For postgraduate research, neither watching video lectures nor just reading a book are going to help you enough.

You're going to have to actively engage with the subject matter, by solving problems, and keeping up with current research literature in journals.

Following on from the OP's comment: I do understand that your question is "which is better - books or videos". And the answer to your question is neither. It's a false opposition.

Neither are necessary, and neither are sufficient. You have to learn the core content of maths and physics by solving problems. And to do postgraduate research, you have to keep up with the current research literature in journals (including preprint archives where appropriate).