HDMI, DisplayPort & USB-C

You've calculated how much data a video signal needs. Now meet the interfaces that carry it. In corporate and commercial AV, three dominate the table and the back of the rack: HDMI, DisplayPort and USB-C. Broadcast and live production add a fourth, SDI.

HDMI

HDMI is the universal language of AV. It carries video, multichannel audio, a control channel called CEC, and the EDID and HDCP conversations you'll meet in the next two lessons — all on one cable. You'll find it on displays, projectors, cameras, set-top boxes and the inputs and outputs of almost every switcher.

The version number tells you the maximum bandwidth the interface was designed for, but the cable has its own certification. A Premium High Speed cable is certified for 18 Gbps (HDMI 2.0 signals); an Ultra High Speed cable for 48 Gbps (HDMI 2.1).

DisplayPort

DisplayPort comes from the computer industry and is standard on business PCs, docks and monitors. It supports MST (Multi-Stream Transport), which lets one port drive several monitors. Many DisplayPort outputs are dual-mode (marked DP++), meaning a simple passive adapter can produce an HDMI signal — handy at a lectern full of HDMI inputs.

USB-C is a connector, not a signal

This is one of the most misunderstood points in modern AV. USB-C describes the shape of the plug. What travels through it depends on what the laptop and the cable support:

• DisplayPort Alt Mode — the port carries a native DisplayPort signal. This is how most laptops send video over USB-C.
• Thunderbolt / USB4 — high-speed tunnelling that can carry DisplayPort video, data and more.
• USB Power Delivery — charging the laptop over the same cable.
• USB data — for cameras, microphones and speakerphones in a meeting room.

That combination is what makes the “one cable at the table” meeting room possible: plug in a single USB-C cable and the laptop gets charged, shows its screen and connects to the room's camera and microphones.

SDI and the legacy you'll still meet

Distance is the real limit

High-bandwidth signals don't travel far over passive copper. As a rough guide, passive HDMI cables become unreliable beyond a few metres at 4K60 rates, and the higher the bandwidth, the shorter the reliable length. For longer runs, AV uses:

• Active optical cables (AOC) — fibre inside an HDMI cable. Often directional: one end must face the source.
• Extenders — a transmitter and receiver over category cable or fibre, covered in Chapter 7.
• AV-over-IP — encode the signal onto the network, covered in Chapter 9.