It's precisely the seeking that kills me. The only interface for seeking a video is a tiny, one-dimensional bar. How do you remember exactly where the right information occurs? On the other hand, text is visible as a whole, and the "seeking" is two-dimensional. Much more efficient to seek. I have a good visual memory and I tend to remember exactly where on a page the formula that I want appears, and just glance away at it without moving any muscles other than my eyes. To seek a part on a video, the process is overwhelmingly more complicated. And then the place where I was before the seek is lost, and you have to seek for it again. Argh!

Thanks for the answer, it turns out that we people are wildly different to each other.