Instead of writing whole sentences, just shorten them.
I used to write things I already knew which is unnecessary, write what you can learn from the notes you write down.
But recently, I started writing my notes in the margin on my textbooks or class books if you don't have any textbooks while the teacher explains. You could use those for videos too (just find the required topic and write them down). This way you have all the info in one book and you don't have to write much down.