“That’s right, in an HDMI cable, nestled amongst the high-speed differential pairs, there’s an exceedingly slow i2c bus.”
The DDC channel exists so a monitor can tell your computer its resolution. It is a plain i2c bus, and tiny OLED screens speak i2c. So he cut an HDMI cable, soldered a display straight onto his laptop’s port and drew pixels over the wrong wires. Completely useless and genuinely brilliant. The spec is behind a registration wall, so hacks like this are how most people learn what is inside the cable.