Use the Matte shader with camera back plate textures or videos. See Setting a camera Front or Back Plane.
To create a 3D matte:
- Drag the Matte shader from the Shaders folder in the Asset browser, and drop it onto your model.
- Select Replace by Type from the context menu that appears.
- In the Matte shader settings, select Highlight Matted Objects to surround the object with a faint outline if you are having trouble viewing the matted objects in your scene.
- Activate Enable 3D Masking option to apply the 3D Matte shader to the selected object. When Enable 3D Masking is not active, the shader appears as a wireframe.
- Activate Adjust Alpha to control the video Alpha channel sent either through your video option board or viewed in the Render window.
- Use the Alpha slider to manipulate the transparency of the Alpha channel. This lets you, for example, make the output slightly transparent so you can pre-visualize characters interacting with live Actors.