Tim Doner - Family Matters: A Look at the Indo-European Languages
Very in depth and interesting lecture about linguistics. Excellent stuff.
It was a bit complex for me to fully grasp on first watch, so I'll probably have to watch it again.
He even discuss and try to demonstrate the logic behind, the seemingly random, irregulars in languages, and how all languages, even from completely different branches, are interconnected and may have a common ancestry, and the predictability and consistency of the phonology changes.
He also speak how they can construct, and make very good guesses, the "root language", even when they have absolute no record of it anywhere.
It is a bit "heavy", university like lecture, and long, so take that in mind before you start watching, but it will help you understand how to be better in languages and understand them overall better. Especially good for learners of multiple languages as a comparative study.
I like one of the comments on Youtube about it, where the guy said, "Tim always has a way of making me feel lazy for only studying ten languages."