PiP Audio
video-mark-audio
Controls whether the picture-in-picture overlay video’s audio is mixed into the output.
video-mark-audio accepts a boolean value. When set to true, the overlay video’s audio track is mixed with the main video’s audio. When set to false (the default), the overlay video is silent in the output. Use video-mark-audio[N] for a specific overlay layer.
Use video-mark-volume to adjust the relative volume of the overlay’s audio when mixing is enabled.