Map MIDI Knob to OBS Chroma Key Tolerance

This article provides a step-by-step guide on how to map a physical MIDI continuous controller (CC) knob to smoothly adjust the chroma key color tolerance (Similarity) in OBS Studio. Because OBS Studio does not support MIDI mapping natively, this guide utilizes the popular, free obs-midi-mg plugin to bridge the connection and configure precise parameter scaling.

Step 1: Install the OBS-MIDI-MG Plugin

To enable MIDI support in OBS Studio, you must install a dedicated MIDI plugin. 1. Download the latest version of the obs-midi-mg plugin from its official GitHub repository or the OBS Resources forum. 2. Run the installer or manually place the plugin files into your OBS Studio installation directory. 3. Restart OBS Studio.

Step 2: Enable Your MIDI Controller in OBS

Once the plugin is installed, you must tell OBS to listen to your specific hardware device. 1. Connect your MIDI controller to your computer via USB. 2. In OBS Studio, click on Tools in the top menu bar and select OBS-MIDI-MG Setup. 3. In the setup window, navigate to the Devices tab. 4. Locate your MIDI controller in the list under “Input Devices.” 5. Check the box to enable Input for your device, then click Apply.

Step 3: Add a New MIDI Binding

Now you will link a physical knob on your controller to the chroma key filter in OBS. 1. Switch to the Bindings tab in the OBS-MIDI-MG Setup window. 2. Click the Add Binding button. 3. Turn the physical CC knob on your MIDI controller. The plugin will automatically detect the MIDI CC number and assign it to the new binding.

Step 4: Map the Knob to the Chroma Key Parameter

Configure the binding to target the correct video source and filter. 1. In the binding configuration panel on the right, set the Action Type to Source Filter Value (or Filter Parameter). 2. Under Source, select the specific camera or capture card source that has your Chroma Key filter applied. 3. Under Filter, select your Chroma Key filter. 4. Under Parameter, select Similarity (this is the technical name for the key-color tolerance slider).

Step 5: Configure Scaling for Smooth Adjustment

MIDI knobs output values from 0 to 127, whereas OBS Chroma Key similarity ranges from 1 to 1,000. Scaling is required for smooth, usable control. 1. In the binding settings, locate the Value Mapping or Scale section. 2. Set the Input Min/Max to 0 and 127 (matching your MIDI controller). 3. Set the Output Min/Max to your preferred tolerance range. While OBS allows 1 to 1000, a practical range for green screens is usually 200 to 600. Restricting the range to these numbers ensures the entire physical rotation of your knob is dedicated only to the usable spectrum, preventing sudden green screen dropouts. 4. Save the settings and close the setup window. Turn your knob to verify that the “Similarity” slider in your source’s filter properties moves smoothly.