PiP Audio Volume
video-mark-volume
Sets the volume multiplier for the picture-in-picture overlay video’s audio when it is mixed into the output.
video-mark-volume accepts a float value. A value of 1.0 preserves the overlay audio at its original level. Values below 1.0 reduce its volume, and values above 1.0 amplify it.
This parameter requires video-mark-audio=true to be set. Use video-mark-volume[N] for a specific overlay layer.