Choosing a 12G-SDI to HDMI converter

A 12G-SDI to HDMI converter takes the SDI output of a camera, switcher or recorder and turns it into an HDMI signal that a monitor, TV or HDMI capture device can accept. If you are building a camera feed for streaming or video calls, the converter is usually one link in a chain: camera, SDI cable, converter, HDMI capture device, computer. This guide covers what to check so that both picture and sound arrive intact.

The short answer, and where the microphone fits

Choose a converter that supports the exact resolution and frame rate your source outputs. Confirm that it passes the embedded audio channels you need, and check whether it can downconvert if your HDMI device cannot handle the full signal. Most of the remaining choice comes down to power, whether you need a loop-through output, and how you configure and update the unit.

This question does not concern a webcam's built-in microphone. A converter has no microphone of its own. It only carries audio that is already embedded in the SDI signal. That audio usually comes from a separate microphone plugged into the camera or into an audio mixer or switcher upstream. If your microphone instead connects straight to the computer, the converter handles video only, and the main concern becomes keeping sound and picture in sync.

Do you need SDI at all?

Many mirrorless and DSLR cameras used as webcams output only HDMI. SDI ports are more common on cinema, broadcast and some camcorder models. SDI uses locking BNC connectors and supports much longer cable runs than HDMI. Those are the usual reasons to run SDI from a camera and convert near the computer or display. If your camera has only HDMI and the computer sits close by, you do not need an SDI to HDMI converter. Some USB capture devices also accept SDI directly, which removes the converter from the chain.

Match the SDI standard to your signal

SDI comes in tiers that are defined by bandwidth. The 12G tier is what lets a single cable carry 2160p (UHD) at up to 60 frames per second. A 12G-capable converter normally also accepts the lower tiers, but confirm this on the spec sheet for any model you consider.

SDI tier | Typical highest format on a single link

HD-SDI (1.5G) | 1080i and 720p

3G-SDI | 1080p at up to 60 fps

6G-SDI | 2160p at up to 30 fps

12G-SDI | 2160p at up to 60 fps

Check the specific frame rates as well as the resolution. Fractional rates such as 23.98, 29.97 and 59.94 are common on professional cameras, and not every converter or display handles every rate. Interlaced SDI formats can also cause trouble on HDMI monitors and capture devices that expect progressive video. If your source outputs interlaced video, look for a converter that deinterlaces, or set the camera to a progressive format.

Check the HDMI side and any scaling

A 2160p60 HDMI signal needs an HDMI output, cable and receiving device with enough bandwidth. That generally means HDMI 2.0 or later. Many USB capture devices, and some older displays, accept only 1080p or limit 4K to lower frame rates. If your SDI source is UHD but your capture device is not, you have two options:

• Set the camera's SDI output to 1080p, if the camera allows it.
• Buy a converter that downconverts UHD to HD on its HDMI output. Simple pass-through converters do not scale, so confirm that scaling is listed as a feature.

Professional SDI video is usually 10-bit 4:2:2. If you work with HDR or log footage, check how the converter handles colour space and HDR metadata on the HDMI side. Also check whether it can apply a LUT for monitoring. Feature sets vary by model.

Embedded audio: what to verify

SDI can embed more audio channels than HDMI typically carries. HDMI devices are commonly limited to stereo or a small multichannel set. As a result, the converter decides which SDI channels reach the HDMI output. For voice capture, check the following:

• Which embedded SDI channels the converter maps to HDMI. Often only the first pair passes by default. If your microphone sits on channels 3 and 4 in the camera, it may not come through.
• Whether the channel mapping can be changed in the converter's settings software.
• Whether the converter has analog or other audio outputs for de-embedding. These let you send the sound to a separate mixer or interface.
• How the capture device presents audio to the computer. Most USB capture devices appear as both a video source and an audio input. You then select that audio input, rather than a webcam or laptop microphone, in your calling or streaming app.

Keep three stages separate when troubleshooting:
Capture: the microphone and the camera's audio input set the quality of the sound in the SDI signal. Mic choice, placement and the camera's gain settings matter most here.
Transport: the converter should pass embedded audio without altering it. It does not add noise suppression or echo cancellation.
Processing: video call apps often apply their own noise suppression, automatic gain and echo cancellation. That processing can change how your voice sounds regardless of the hardware.
Speaker playback on the far end is a separate path again. Poor sound on someone else's speakers is not necessarily a converter fault.

Lip sync when the microphone bypasses the camera

Every stage in the chain adds some video delay: camera processing, conversion and capture. This is especially true if the converter scales or deinterlaces. If your microphone plugs into an audio interface or USB port on the computer, your voice can arrive ahead of your picture. Streaming software usually lets you add a delay or sync offset to an audio source to correct this. Many video call apps do not offer that option. In those apps, embedding the microphone audio upstream so that it travels with the video can be the more reliable route. No measured latency figures were available for this guide, so judge sync on your own setup.

Practical buying checklist

• SDI input tier supports your source format, including the exact frame rate.
• HDMI output version and your capture device or display can handle that format, or the converter downconverts.
• Embedded audio channel mapping matches where your microphone sits in the SDI signal.
• Audio de-embed outputs, if you need to route sound separately.
• Loop-through SDI output, if the same feed also goes to a recorder or monitor.
• Power method: USB, a locking DC connector, or a battery or plate option for mobile rigs.
• Setup and firmware software is available for your operating system.
• Cables are rated for 12G operation. Longer runs at 12G are more demanding than at lower rates, so check the cable maker's rated length.

About Blackmagic and other brands

Blackmagic Design is a frequent search term here because it sells compact SDI to HDMI converters, including 12G-capable models in its converter lines. Other broadcast and video accessory makers also offer 12G-SDI to HDMI units. Formats, scaling, audio mapping and configuration options differ from model to model and can change with firmware updates. Confirm each feature on the manufacturer's current specifications before buying.

What this guide could not confirm

No verified model specifications, prices, availability or independent test results were available when this guide was prepared. The points above are general principles of SDI and HDMI signal handling, not measured performance of any product. For current US pricing and stock, check retailer listings and note the date. Treat manufacturer specifications as claims rather than test results.