Mark Brown analyzes the design of dungeons in Zelda for each episodes of the license. (The Game Maker's Toolkit serie is awesome too)

From episode 1 to 24 Daniel Floyd and James Portnow deconstruct the first part of Dark Souls I ranging from level design to UI decisions.

The whole channel is a mine of gold. Extra Credits / Design Club / James recommends / Extra Frames discuss topics ranging from place of the game industry in the society to details of the animations in games. Plus Extra History and Extra Sci Fi treat subjects that don't get enough attention otherwise.

Multiple interviews, driven by Double Fine staff, of lead designers of classic action platformer games while playing their landmark titles. Season 1 is also a must-see about a wider range of genres.

Documentary by 2 Players Production covering the full development cycle of Broken Age by Double Fine inside their studio. It's a realistic look at what is game development on a daily basis throughout a whole project.

A serie teaching every math principles that are used in game development. Starting with the basis of vector mathematics and goes up to Runge-Kutta methods.

Casey Muratori streams the realization of a complete game written in C starting from scratch: no libraries, no frameworks, no engines! This is an incredibly valuable lesson on how to program a game and how mid to low level stuff works.

Unity channel where they store every occidental Unite conferences and a lot of tutorials introducing new features and specific systems. (For Unite Seoul look for Unity Korea)

A cycle of conferences taking place in Norway and recorded on Youtube every year since 2012.

A cycle of conferences taking place in Sweden and recorded on Youtube every year since 2016.

The free archives of GDC conferences on Youtube.

This Youtube channel is dedicated to information technologies, electronics and video game hardware. There's a lot of tutorial on how to disassemble, clean, repair and modify consoles and gamepads.