Create Dynamic Alpha Masks in OBS with Color Source

This guide explains how to use the “Color Source” in OBS Studio to create custom, dynamic alpha masks for your scenes. By leveraging OBS groups and source blend modes, you can utilize simple color blocks to dynamically reveal, hide, or shape your video feeds and graphics without needing external video editing software or static image files.

Step 1: Create a Group for Masking

OBS Studio applies blend modes to sources relative to the other sources inside the same Group. Creating a group is essential to prevent your mask from affecting your entire scene.

1. Go to the Sources dock in OBS.
2. Right-click an empty space, hover over Add, and select Group (or select your target video source, right-click, and choose Group Selected Items).
3. Name the group something recognizable, such as “Dynamic Mask Group.”

Step 2: Add Your Target Media and Color Source

Next, you need to place both your video feed and the Color Source inside the group container.

1. Drag your main media source (like a webcam or gameplay capture) inside the Group.
2. Right-click inside the Group, select Add, and choose Color Source. Name it “Mask Shape.”
3. In the Color Source settings, click Select Color and choose White (#FFFFFF). Set the width and height to match the size of the mask shape you want to create, then click OK.
4. Ensure the Color Source is positioned above your main media source in the group hierarchy.

Step 3: Configure the Blend Mode

To turn the Color Source into an active mask, you must change its blending behavior.

1. Right-click the Color Source (“Mask Shape”) inside your Group.
2. Navigate to Blend Mode in the context menu.
3. Select Multiply.

Because you selected Multiply, only the area of your video feed covered by the white Color Source will remain visible. The areas outside the white box (the empty space of the group) will become transparent, effectively masking your video.

Step 4: Make the Mask Dynamic

Now that the mask is functional, you can animate or manipulate the Color Source to create dynamic transitions, reveal effects, or custom overlays.

• Smooth Transitions: Use the Show/Hide Transition settings on the Color Source. Right-click the Color Source, go to Show Transition, and select Slide or Fade. When you toggle the visibility of the Color Source, the mask will dynamically sweep or fade across your video.
• Movement and Animation: If you have the Move Transition plugin installed, you can apply a “Move Value” filter to the Color Source to continuously slide, bounce, or rotate the mask across the screen.
• Adjusting Opacity: Open the filters menu for your Color Source and add a Color Correction filter. Lowering the opacity of the Color Source will dynamically fade the mask and semi-transparently reveal the background.