Video bandwidth
Putting it together: calculate the data rate of a video signal and check it against a link.
You now know the four ingredients of a video signal: resolution, frame rate, bit depth and chroma. Multiply them together and you get its bandwidth — the data rate every cable, switcher, extender and network link in the path must carry. This one number decides more AV product choices than any other.
The formula
Bits per pixel comes from bit depth and chroma. At 4:4:4, each pixel carries three full channels, so 8-bit colour means 24 bits per pixel. At 4:2:0 it's half that.
Take 1080p at 60 fps, 8-bit, 4:4:4:
That's about three billion bits every second, for one ordinary laptop signal. Now try the same maths for 4K: four times the pixels, so four times the data — almost 12 Gbps before anything else is added.
The hidden extra: blanking
Digital video interfaces inherited a habit from analog CRTs: after each line and each frame there's a pause called the blanking interval. Today that time carries audio and auxiliary data, but it still occupies the link. Standard timings for 1080p and 4K add about 19% on top of the visible picture. That's why 1080p60 is usually quoted as about 3.6 Gbps rather than 3.0, and 4K60 at 8-bit 4:4:4 as about 14.3 Gbps.
24
11.94 Gbps
14.26 Gbps
Uncompressed estimate using an HDMI-style model and 60 Hz CTA-861 blanking ratios — real timings vary slightly by format. HDMI carries 4:2:2 in a fixed 24-bit container. Compression (such as DSC) and vendor-specific extender technologies are not included.
Raw rate vs. usable rate
Interface specs quote a raw signalling rate, but some of those bits are spent on line coding — extra bits that keep the receiver locked and detect errors. What's left for video is the usable (payload) rate.
| Link | Raw rate | Coding | Usable for video |
|---|---|---|---|
| HDMI 1.4 | 10.2 Gbps | 8b/10b | 8.16 Gbps |
| HDMI 2.0 | 18 Gbps | 8b/10b | 14.4 Gbps |
| DisplayPort 1.4 | 32.4 Gbps | 8b/10b | 25.92 Gbps |
| HDMI 2.1 | 48 Gbps | 16b/18b | ≈ 42.7 Gbps |
- HDMI 1.4
- Raw rate10.2 Gbps
- Coding8b/10b
- Usable for video8.16 Gbps
- HDMI 2.0
- Raw rate18 Gbps
- Coding8b/10b
- Usable for video14.4 Gbps
- DisplayPort 1.4
- Raw rate32.4 Gbps
- Coding8b/10b
- Usable for video25.92 Gbps
- HDMI 2.1
- Raw rate48 Gbps
- Coding16b/18b
- Usable for video≈ 42.7 Gbps
8b/10b coding, for example, sends 10 bits on the wire for every 8 bits of data, so only 80% of the raw rate is available. Always compare a signal against the usable figure.
Why this shapes product choices
- Switchers are rated by the bandwidth each input and output can handle. An 18 Gbps switcher can carry 4K60 4:4:4 at 8-bit, but not at 10-bit.
- HDBaseT extenders are generally designed around the same 10.2 Gbps-class signals as HDMI 1.4, so 4K60 typically needs 4:2:0 or some form of compression.
- AV-over-IP runs on 1 Gbps or 10 Gbps network links. Even 1080p60 uncompressed exceeds 1 Gbps, which is why most AVoIP systems compress — a trade-off you'll study in Chapter 9.
- Cables are certified for bandwidth: a cable rated for 18 Gbps may fail at 48 Gbps.
Key takeaways
- 01Video bandwidth = width × height × fps × bits per pixel, plus blanking overhead.
- 02Standard 1080p and 4K timings add about 19% blanking on top of the visible picture.
- 03Compare against a link's usable rate, not its raw rate — line coding takes a share.
- 044K60 8-bit 4:4:4 just fits HDMI 2.0's 14.4 Gbps; 10-bit does not.
- 05When a signal doesn't fit, you trade frame rate, bit depth, chroma, resolution — or compress.
Check your understanding
Q1Roughly how much uncompressed data does 1080p60 8-bit 4:4:4 carry, including blanking?
Q2HDMI 2.0 is quoted as 18 Gbps. How much of that is usable for video?
Q3A 4K60 10-bit 4:4:4 signal won't fit through an HDMI 2.0 switcher. Which change makes it fit while keeping 4K60?