Text Background Radius
txt-radius
Sets the border radius of the text background box for a video text overlay.
txt-radius accepts an integer in pixels, rounding the corners of the background box set by txt-bg. Use txt-radius[N] to set the radius for a specific text layer.
This parameter works identically to txt-radius in the Rendering API.
For the full list of text overlay parameters, see the Text Overlays overview.