This video is a bit older now (over one year), but I just found about it. And I want to share it here, because it was very well explained, without boring stock videos or background music. It's just like a teacher would teach you, but with some enthusiasm behind it. I enjoy his videos so far.

• Watch on YouTube: https://youtu.be/Zkv8sW6y3sY
• Watch on Invidious, a more private and indirect way to watch: https://inv.nadeko.net/watch?v=Zkv8sW6y3sY

Video description:

Why is the speed of light the same in all reference frames? Let's rediscover the thought experiments that led Einstein to his special theory of relativity

Chapters:

00:00 Introduction
01:15 1/3 Detect motion with particles? (Thought experiment)
04:01 Inertia doesn't allow detecting constant velocity motion
06:18  2/3 Detect motion with waves? (Thought experiment) 
09:18 Medium doesn't allow detecting constant velocity motion
10:15 Constant velocity motion is RELATIVE!
11:02 3/3 Detect motion with light? (Thought experiment)
13:12 Does light break relativity? 
13:46 Michelson & Morley's experiment (oversimplified) 
14:20 The logical conclusion - Speed of light is same in all frames