> For the complete documentation index, see [llms.txt](https://captivatehelp.newbluelive.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://captivatehelp.newbluelive.com/set-up-your-production/chapter-index-7/use-with-an-sdi-broadcast-switcher.md).

# Use Captivate with an SDI broadcast switcher

Use this setup in an SDI-routed production, where a broadcast switcher composites graphics from a paired **fill** and **key** feed. Captivate sends fill and key on two SDI connectors, and the switcher’s keyer lays the graphics over its program. This is the path for Sony, Ross, Grass Valley, FOR-A, Blackmagic, and similar production switchers.

## When to use this setup

* The switcher accepts SDI key + fill (an upstream or downstream keyer).
* Your facility routes video over SDI.
* You need broadcast-quality keying with no software-compositing overhead on the switcher side.

## Recommended path

Send **SDI key + fill** from Captivate into the switcher’s keyer. Captivate drives a fill output and a matching key output on a supported SDI card; assign them to the keyer’s fill and key inputs.

Alternatives:

* If the facility runs on NDI or OMT instead of SDI, send graphics over the network with alpha — see [the network-overlay path](/set-up-your-production/chapter-index-7/use-with-vmix.md).
* If the switcher has no fill + key input but can chroma key an HDMI feed, use [an HDMI switcher setup](/set-up-your-production/chapter-index-7/use-with-an-hdmi-switcher.md) instead.

## Alpha Key

Turn **Alpha Key** on. With Alpha Key on, SDI runs in **key + fill** mode and uses two connectors — one for the key, one for the fill. With Alpha Key off, SDI runs one connector per channel and sends an opaque image, which a key + fill keyer cannot use. If your receiving system shows incorrect edges, set straight or premultiplied alpha to match it — see [Set the project format](/set-up-your-production/set-up-your-project.md).

## Set up overview

1. Set the project’s video format to match the switcher’s standard exactly — resolution, frame rate, and interlacing — and turn **Alpha Key** on. See [Set the project format](/set-up-your-production/set-up-your-project.md).
2. From the **Program Out** menu, choose **SDI** and select your card. Confirm it is in key + fill mode.
3. Cable the fill and key outputs to the switcher’s keyer fill and key inputs.
4. On the switcher, assign those inputs and configure the upstream or downstream keyer.

## Detailed setup links

* [Output graphics with SDI](/set-up-your-production/chapter-index/output-graphics-with-sdi.md) — card setup, key + fill, and the internal keyer option.
* [Set the project format](/set-up-your-production/set-up-your-project.md) — matching the switcher’s format and setting Alpha Key.

## Related

* [Use Captivate with ATEM](/set-up-your-production/chapter-index-7/use-with-atem.md) — for ATEM models with SDI fill + key.
* [Choose how Captivate fits your production](/set-up-your-production/how-it-fits-your-production.md) — the decision hub.


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