Elgato Cam Link 4K A/V Sync and OBS Setup

Elgato Cam Link 4K A/V Sync: Fix Audio Sync with a Capture Card Setup

Measure the full HDMI capture stack before entering any OBS delay. Cam Link 4K connects a DSLR or mirrorless camera to your computer through HDMI, then presents that camera feed as a USB webcam for streaming, video calls, and recording.¹

That capture stage changes how you should measure sync. Instead of applying a generic webcam offset, run the 5-clap test with the exact camera, HDMI mode, USB port, microphone, and recording software you plan to use. Then enter the measured value in OBS Sync Offset for the audio source you selected during the test.²

Why Cam Link A/V sync differs from USB webcam sync

A native USB webcam sends its own processed video stream directly to the computer. Cam Link 4K takes a camera's HDMI output, converts it through the capture device, and exposes the result as a USB video source.¹ Windows also provides a system-supplied USB Video Class driver for UVC devices, which is why class-compliant capture devices can appear as webcam-style video sources without a custom driver.³ The browser cannot know how much time your camera spent preparing the HDMI feed before the capture device converted it, so the full stack needs one measurement.

The audio path matters just as much as the video path. If your microphone is a separate USB device, the browser compares that audio input against the Cam Link video input. If you choose HDMI audio from the camera instead, you are measuring a different audio path for the same video feed. Keep that audio path consistent between measurement and correction.

Audio path selection before OBS

This is why a Cam Link setup should not borrow an offset from another creator's setup. A different camera body, HDMI output mode, USB port, or audio input can change the timing relationship, even when the same capture card remains in the chain. Selecting the wrong audio input for the measurement produces a correction that targets a different pipeline than the one OBS actually records, which can make the sync worse instead of better.

Pick one audio input and keep it for both the measurement and the correction. If the browser dropdown shows both HDMI audio and a USB microphone, the choice decides which pipeline the measured number describes. Switching inputs between the two steps silently changes the audio side of the offset, so the OBS correction ends up applied to a path the recording never used.

Measuring the offset for a Cam Link setup

Select "Elgato Game Capture HD" or "Cam Link 4K" as the video input in the browser dropdown. Choose the microphone you will actually use, whether that is a separate USB microphone or the camera's HDMI audio input. Run the 5-clap test with the camera connected to the Cam Link and the Cam Link connected to a USB 3.0 port.⁴

Use the fastest shutter speed your lighting allows before the test. A fast shutter freezes the clap motion and makes the luminance edge easier to timestamp, while a slow shutter spreads hand movement across the exposure and softens the visual transient.⁵ If 1/250s is too dark, use the fastest practical setting and keep it fixed while you repeat the five claps.

After the first run, repeat the test once or twice without changing the camera, USB port, microphone, or OBS settings. If the spread is wide, check focus, exposure, and hand motion before trusting the average. A stable average is more useful than a single measurement that happened to land cleanly.

Applying the correction in OBS

After measuring, enter the offset in OBS Advanced Audio Properties for the audio source you tested. OBS exposes the sync offset control as a millisecond spin box and converts the entered value to nanoseconds when applying it to the source. The conversion from milliseconds to nanoseconds happens internally, so you always think and enter values in milliseconds regardless of the internal precision OBS uses for the actual audio delay calculation.²

Because Cam Link sits between the camera and the browser, the correction should match the complete capture stack. Do not subtract a generic USB webcam offset or reuse a value from a different camera body. If you swap cameras, change HDMI output settings, move the Cam Link to another USB port, or change the audio input, run the 5-clap test again and update the OBS value. The Cam Link's FPGA encoding stage adds a consistent base latency on top of whatever the camera's HDMI output contributes, so the total offset is always the sum of both stages and cannot be estimated from camera specs alone.

Re-measuring after switching cameras on the Cam Link

Swapping camera bodies on the same Cam Link requires re-measuring the A/V offset. The capture card may be the same, but the camera can output a different processed HDMI signal with different internal encoding latency. Record each camera's measured offset so you can restore the correct OBS Sync Offset quickly after a swap. Label each value with the camera model and HDMI output mode so you can pull up the right number without re-running the test every time you change bodies.

HDMI audio versus external microphone pairing

If you use HDMI audio from the camera, measure with that HDMI audio input selected. If you use a separate USB microphone, measure with that microphone selected. Those are different audio paths, and one OBS value cannot correct both pairings accurately. Keep notes for each pairing so you can restore the right correction when you switch between HDMI audio and an external mic.

When to use this

Run this test when setting up an Elgato Cam Link 4K or similar HDMI capture card for the first time, when switching to a new camera body in an existing Cam Link setup, or when OBS recordings show a lip-sync gap that a standard USB webcam offset correction did not fix.

Examples