Text Background Color
txt-bg
Sets the background color of the text box behind a text overlay on video.
txt-bg accepts a hex color value (without the # prefix). An optional two-digit alpha suffix controls opacity — for example, 00000080 is black at 50% opacity. Use txt-bg[N] to set the background for a specific text layer.
This parameter works identically to txt-bg in the Rendering API.
For the full list of text overlay parameters, see the Text Overlays overview.