What is inside my HDMI switch?

The chip labeled AS1221 functions as the main HDMI multiplexer/switch IC.

While this specific part number is typically found in budget-friendly or unbranded electronics and lacks a widely public datasheet, its physical layout on the circuit board clearly gives away its role.

Here is exactly what it does inside your device:

• Signal Routing: It acts as the traffic director for the device, actively switching the high-speed video and audio signals from multiple HDMI input ports and routing your selected input to the single HDMI output.
• TMDS Data Handling: The parallel lines (traces) you can see connecting to the pins at the bottom of the chip are high-speed differential pairs. These carry the TMDS (Transition-Minimized Differential Signaling) data—specifically the three data channels and one clock channel required to transmit an HDMI signal.
• Signal Equalization: HDMI switches cannot simply cross wires together; the signals are too complex. This IC takes in the digital signal, cleans it up, and amplifies it (re-driving) before sending it to the output to prevent visual artifacts or signal drops caused by cable length.