After watching YouTube lecture of Frederic Schuller, I am quite impressed with his lecture. Since I am not a student anymore and presently as of interest I am studying Lie algebra independently which is of course not a easy task. This YouTube lecture has given me valuable insight into basics of Lie algebra.
Can anybody please suggest more of such YouTube lectures on Lie algebra and Lie groups as well?
Ok, I've seen most of courses on YT so I can give you a little review:
Heluani, Introduction on Lie Algebras: it follows Kaç lectures that were given in MIT and so you can also download the lectures and exercises. Anyway half of the lectures are in Portuguese and anyway I wouldn't suggest this approach as a first try.
Ziller, Lie Groups and Representation Theory is really interesting and all in English, but it's quite advanced and focused on the Geometry part and essentially more on Lie Groups rather than Lie Algebras. But has a lot of examples and gives you a kind of big picture on why are doing this stuff.
This guy, Lie Algebras and their representation it's indeed really a point where to start. Is really slow, pedantic, follows almost literally Erdmann's book, gives exercises, so I think could be your first try.
Lie Algebras School, was a school of 15 days on Lie Algebras and their representations. They follow Humphrey's book and they are halfway between an easy start and an intermediate presentation.
I would avoid (and really avoid) any introduction from Physicist. I like the synthesis that Schuller makes and actually I don't think you will find a better introduction from a physicist. I've seen some presentations from PIRSA. Generally speaking the notation might confuse you and generally speaking they are not rigorous at all, their mathemathics have to be interpreted and often as mathemathician is not trustworthy.
Last but not least I would suggest you to read Brian Hall, An elementary Introduction to Group and their representation. I know it's a book, I know is focused on Lie Groups rather than Lie Algebras, but I think that before going to study Lie's Algebras you should have a picture of why are you studying them, how are originated from a geometric and an algebric point of view an this book I think is the best to begin with.
Last suggestion: if you're interested into Lie Algebras from a Physics point of view, then I would suggest to first study Lie's Algebras from a mathematic point of view and then read once Gilmore's book "Lie Groups, Physics, Geometry" and or "Georgi, Lie Algebras in Particle Physics". But I think you should approach the subject from a mathematical point of view to fully understand what they're doing.