How to Connect an SDI Source to an HDMI Capture Input

The short answer

You cannot connect an SDI output to an HDMI input with a simple adapter or passive cable. SDI and HDMI are different electrical signals with different connectors, so something has to actively convert one into the other. The usual chain is: camera SDI output, coaxial cable with BNC connectors, an SDI-to-HDMI converter, an HDMI cable, and then your HDMI capture device, which connects to the computer over USB or another interface.

Products sold as an "SDI to HDMI cable" fall into two groups. Some are just cables with an adapter on the end, and they will not work. Others have converter electronics built into the cable or a small housing on it. Those can work, but they are still converters. They usually need power and must support your camera's video format. Before buying, check that the product description names it as a converter and lists the formats it handles.

Direction matters. SDI-to-HDMI and HDMI-to-SDI converters are different devices, and most only work one way. Some bidirectional models exist, so read the label rather than assuming.

Check whether you need SDI at all

SDI (Serial Digital Interface) is a professional video connection carried over coaxial cable with a locking BNC connector. It is typically found on broadcast and cinema cameras and on professional camcorders. Most consumer DSLR and mirrorless cameras output HDMI only. If your camera has an HDMI port, you can connect it straight to an HDMI capture device and skip this setup. Some capture devices also accept SDI directly. If you have one of those, you do not need a separate converter.

What to confirm before connecting

• SDI standard: SDI comes in several speeds, commonly labeled SD-SDI, HD-SDI, 3G-SDI, 6G-SDI and 12G-SDI. The converter's SDI input has to support the standard your camera outputs.
• Resolution and frame rate: the camera's output format must be accepted by the converter and by the capture device. A converter that passes a signal is no use if the capture device rejects that frame rate.
• Progressive versus interlaced: some capture devices and apps handle interlaced signals poorly. If the camera offers a progressive output such as 1080p, it is usually the safer choice.
• Power: the converter needs its own power from an adapter or a USB power source. It will not draw power from the SDI line.
• Cables: use 75-ohm coaxial cable rated for your SDI standard. Higher-speed SDI is more sensitive to cable quality and length. HDMI is generally less tolerant of long runs, so place the converter near the capture device and run the longer distance over SDI.

Step-by-step connection

• 1. In the camera menu, set the SDI output to a format the converter and capture device both support. Turn off on-screen overlays on that output if you don't want menus and indicators in the picture.
• 2. Power the converter.
• 3. Connect a BNC cable from the camera's SDI OUT to the converter's SDI IN. Push and twist the BNC connector until it locks.
• 4. Connect an HDMI cable from the converter's HDMI OUT to the capture device's HDMI IN.
• 5. Connect the capture device to the computer.
• 6. Open a camera or capture app and select the capture device as the video source. Then select it in your call or streaming software.

Verify each stage separately

There are three different checks in this chain, and passing one doesn't mean passing the next:

• Signal at the converter: many converters have a status light for a detected input. What the lights mean varies by model, so check its manual.
• Capture: the computer listing the capture device only means it is connected. Successful capture means a live, correctly framed image from the camera appears in the app.
• Call quality: a good captured image can still look worse in a call. Call apps compress video and may limit resolution based on bandwidth and their own settings.

If the app or browser shows no image at all, also confirm that it has permission to use the camera in your operating system's privacy settings and in the browser's site permissions. A denied permission looks the same as a dead signal.

Audio over SDI

SDI can carry audio embedded in the video signal, and many converters pass embedded audio through to HDMI. The capture device may then appear on the computer as a separate audio input. Audio still has to clear three separate hurdles. The input has to show up on the computer, the level meter has to move when the source makes sound, and the sound itself has to be intelligible. Whether embedded audio passes through, and which channels, depends on the specific converter and capture device. Check their documentation. If you use a separate USB microphone instead, choose that microphone in the call app and mute the capture device's audio to avoid echo or doubled sound.

Troubleshooting

Symptom | Likely cause | What to try

No signal light on the converter | Camera SDI output disabled, unsupported format, loose BNC, no power | Enable SDI output in the camera menu, reseat the cable, confirm the converter is powered, try a simpler format

Converter shows signal, capture app shows black or no signal | Capture device does not accept the format, HDMI cable or port issue | Change the camera to a common progressive format, swap the HDMI cable, reconnect the capture device

Image flickers, drops out or shows sparkles | Cable not rated for the SDI speed, run too long, damaged connector | Use a shorter or properly rated 75-ohm cable, or drop to a lower SDI standard

Image works in the capture app but not in the call app | Wrong source selected, permission denied, device held by another app | Pick the capture device in the call settings, check permissions, close other apps using it

Picture is fine but no sound | Audio not embedded, not passed through, or wrong input selected | Check camera audio settings, check converter and capture device audio support, select the correct input

Limits of this guide

This guide follows the general principles of SDI and HDMI connections. It doesn't cover specific converters, capture devices or prices, and it includes no tested results, because no product-specific evidence was available. Supported formats, audio handling, power requirements and status indicators all differ between models. Confirm them in the manufacturer's specifications for the exact devices you plan to use.