Video lectures are a good way to clear the concepts,but the process can be lengthy and now with only around 4 months remaining for gate cse 2018,it may hinder your progress.Here I am giving you some strategy you can use if you rely on video lectures for clearing your concept-
(1)Dont watch video lectures like a movie or tvserial.The biggest problem with watching video lectures is you understand all the concepts and problems at the time of watching the lecture because the professors are so high class and they make thing crystal clear for you,but after some days you realise you have a hard time remembering a concept or how to approach a familiar problem.
What you can so is divide lectures into some parts and have a pen and copy ready with you.And then first try to give some effort to the learn the concept.If you have some doubt then go the respective part in video lecture and try to understand it.
Wikipedia is the most underrated thing,please make a habit of reading wikipedia for everything.It may look just a page but it contains all the details and atleast a example.Try to understand that example first and fully understand it.
So focus on learning the basic concept ,work out that example ,that basic problem yourself and give some time to it.atleast half an hour.
So after you are not able to understand a concept ,you can see the respective lecture and jump to the part you are not understanding.