HDMI to DP for a Capture Card: Latency and HDCP

October 31, 2026

By ZONG Editorial Team | ZONG technical guide

Quick answer: 1080p120 at 8-bit 4:4:4 needs about 8.9 Gbps, which sits comfortably inside both HDMI 2.0 at 18 Gbps and DP 1.2 at 21.6 Gbps. The real limits are the converter core, its added delay and HDCP. A plain converter adds 2 to 5 ms and is invisible in a recording. A converter with a scaler adds one or two frames, which is enough to shift audio sync and to make passthrough feel late.

A capture chain fails in ways that look like the capture card but are not. When a converter is inserted between a console or camera and a DisplayPort capture input, it adds a few milliseconds, re-times the video into a new framing and re-publishes the EDID. Dropped frames, a black recording and a passthrough monitor that lags the game can all trace back to that one part.

Where the converter sits in a capture chain

There are two ways to place the part. In a loop-through design, the source feeds the capture card, the card’s HDMI output feeds a converter, and the converter feeds a DP monitor. In a split design, a splitter feeds the capture card and the monitor separately. Both work, but only the loop-through design puts the converter in the viewer’s path, where its delay is felt rather than measured.

That placement decision matters more than the converter’s specification. A part that adds 3 ms is irrelevant inside a recording and noticeable in a competitive shooter when it sits between the console and the display. Decide which path the converter belongs on before comparing models.

The passthrough port is not a clone

On most capture cards the passthrough output is a separate stream, re-clocked from the card’s own receiver. It is not a passive copy of the input. If the converter on that output negotiates a lower mode, the capture can stay at 1080p120 while the monitor drops to 1080p60, and the operator sees stutter that never reaches the file. Always read the mode on the display, not only in the capture software.

1080p120 needs headroom, not a spec sheet

1080p120 is modest in bandwidth, so almost any DP 1.2 part can carry it. What breaks is timing consistency: a converter that re-times frames with a shallow buffer will hold 120 Hz for minutes and then repeat a frame. On a 60 second capture we look for zero repeated frames; one repeat per thousand frames is enough to fail the sample.

The latency budget, measured

The figures below come from a frame counter photographed at both ends of the chain, averaged across five runs, and describe our own parts rather than every product on the market.

Reading dropped frames correctly

Dropped frames in the file have three common causes: USB bandwidth shared with other devices, an encoder setting above what the host can sustain, and a source frame rate that does not divide evenly into the recording rate. Converter delay alone does not drop frames, it shifts them. If the file shows a constant offset in audio sync rather than missing frames, look at delay. If it shows missing frames, look at the bus.

HDCP and the black screen

Protected content will not record. A compliant converter passes the HDCP handshake through and the capture card refuses the stream, which appears as a black recording with a valid signal indicator. That is the correct behaviour, not a fault. Converting the interface does not change the rights status of the content, and no part we supply is intended to bypass it.

Stage	Added delay	Effect at 60 fps	What to do
HDMI cable, 2 m	Under 1 ms	None measurable	Keep runs short
Plain converter	2 to 5 ms	Under one frame	Acceptable in loop
Converter with scaler	16 to 33 ms	One or two frames	Match the mode instead
MST hub in chain	1 to 2 ms	None on one stream	Fit only if needed
Capture encoder	30 to 80 ms	Recording only	Keep out of passthrough

Two capture setups

Both of these were built to record at 1080p120 and both needed a change after the first test session.

Console at 1080p120 into a DP capture input

The console fed the capture card by HDMI, and the card’s passthrough went to a converter and then to a 1440p DP monitor. The monitor accepted 1080p120 and scaled internally, so the converter stayed in a plain pass-through mode. Measured delay from console to display was 4 ms, and a 30 minute capture at 1080p120 held 60 fps output with no repeated frames in the passthrough path.

Camera feed into a streaming PC

A studio camera output 1080p60 through a converter into a DP input on a small form factor encoder PC. The first attempt recorded with audio drift of about 120 ms over ten minutes. The cause was the camera’s own output timing, not the converter: a direct HDMI capture path reproduced the same drift.

Choosing the split, not just the adapter

If the viewer and the recorder both need the signal, a splitter plus two short paths beats one converter with two outputs. Splitters duplicate the stream before any re-timing, so the monitor path stays clean and the capture path takes whatever delay the card adds. A converter with two outputs generates the second from the same re-timed stream, adding a second point of failure.

Where the source is HDMI only and both destinations are DisplayPort, one converter per destination is the honest answer. Two converters on one source each negotiate independently, so a fault in one does not drag the other down, and the bill of materials stays simple when a unit is replaced later.

Frequently asked questions

Does a converter add enough lag to matter in a recording?

Not in the file. A plain converter adds 2 to 5 ms, which is under a single frame at 60 fps. Lag matters on the passthrough display, and only a converter with a scaler adds a full frame or two.

Why is my capture black when the monitor still works?

Almost always HDCP. The converter passes the handshake through and the capture card rejects protected content while the display, which is allowed to show it, keeps working normally.

Can one converter feed a monitor and a capture card?

Some units offer two outputs, but a splitter before the converter is more predictable. It keeps the monitor path free of re-timing and lets each destination negotiate its own mode.

Will 1080p120 survive the conversion?

Yes at 8-bit 4:4:4, which needs about 8.9 Gbps and fits inside DP 1.2. Confirm the monitor accepts 120 Hz natively rather than through internal scaling, or the extra frames are discarded.

What causes audio drift in a capture?

A source clock that does not match the capture clock. Test with a direct path before blaming the converter, then resample audio in software if the drift is small and constant.

Next step

Tell us the source frame rate, the capture card model and the monitor mode, and we will map the chain and flag where delay or HDCP will bite. Request the review at https://zh-zong.com/contact/, email zongcarrie@zh-zong.com or call +86 13543026126. Sample units can be supplied with a frame-count test log.