Why can’t my Disguise VX4+ with a VFC HDMI 2.0 card output 4 K @ 60 Hz 10‑bit 4:4:4?
(…and why the same hard limit applies to a Brompton Tessera SX40 or any other processor that exposes an HDMI 2.0 socket)
1 · The myth that “HDMI 2.0 handles everything”
Question: What if someone promises you True 4K 10-bit 4:4:4 over HDMI 2.0 on your Volume (video wall)?
Disguise VFC Cards data sheet
“The spec says 18 Gb/s. Shouldn’t that be plenty for 4 K @ 60 Hz, 10‑bit, RGB 4:4:4?”
The connector is willing; physics is not. HDMI 2.0 tops out at 18 Gb/s of useful payload, and that cap is before we add protocol overhead. But wait… Real life HDMI 2.0 bandwidth is 14,4 Gb/s.
Let’s do the math:
Parameter
Value
Resolution
3840 × 2160 px
Refresh
60 Hz
Bit‑depth
10 bits per channel
Chroma
4:4:4 (RGB, no subsampling)
Quick math – Active pixels only: 3840 × 2160 × 60 fps × 30 bit ≈ 14.93 Gb/s Add blanking pixels plus 8b/10b TMDS overhead and we land around 21 Gb/s – well beyond HDMI 2.0’s runway.
Therefore something has to give:
Drop to 8‑bit ➜ 4 K @ 60 8‑bit 4:4:4 fits.
Keep 10‑bit but subsample to 4:2:2 or 4:2:0.
(A quick recap on 8b/10b and blanking is coming soon in another post.)
2 · “But my VX4+ is ‘quad‑4K’!”
Yes – but each VFC output is still plain HDMI 2.0. The VX4+ render pipeline could push 12‑bit, yet when the signal hits that socket it must squeeze into 18 Gb/s.
Full HDR, slight chroma softening; most LED walls won’t show it.
Perfect chroma
4 K @ 60 8‑bit 4:4:4
No subsampling, but limited grey steps.
Have both
4 K @ 60 10‑bit 4:4:4 over DP 1.4, 12G‑SDI, or HDMI 2.1
Not possible through a VFC HDMI 2.0 card.
5 · Common questions I get on set
Can I slice the wall into four quarter‑feeds (each 4 K @ 60 8‑bit) and stitch them? Yep – each feed stays under 18 Gb/s.
Will 4:2:2 look bad on camera? Only on razor‑sharp edges or heavy crops. Feature films run 4:2:2 10‑bit all the time.
What if I drop to 50 Hz or 30 Hz? Halving refresh frees bandwidth: at 30 Hz you could do 4 K 10‑bit 4:4:4 – but you lose the 60 p motion feel.
Why not HDMI 2.1? Because, today (2025), disguise offers no HDMI 2.1 VFC… yet.
6 · “True 4K” marketing in the wild
NovaStar’s H‑Series datasheet claims:
True 4K — 4K × 2K @ 60 Hz, RGB 4:4:4, 10‑bit.
Read the fine print: They rely on dual HDMI 2.0 cables (each 2 K wide) or a DP 1.2 input using CVT‑RB (Coordinated Video Timing – Reduced Blanking). The headline is true, but only when you split the payload or use RB timing to trim blanking pixels. One cable alone won’t carry that load.
7 · Designer’s own disclaimer
“When using 4K 50/60 Hz over HDMI 2.0, chroma subsampling 4:2:2 is required. Designer currently produces 4:4:4 EDIDs, so you must change the setting in the GPU control panel.” (Designer r27, page 1902)
Translation: HDMI 2.0 can’t push 4k@60Hz uncompressed 10‑bit 4:4:4. They’re not hiding anything; we just need to read the numbers.
