With vjMixer, you can overlay video, audio on the output.
In the Overlay dialog, select the overlay mode first, such as 1/9 view, 1/4 view, full view.
Then select the position where you want to overlay the video by click the number position button.
Click the Directory button to select the media file, then click the Play button to overlay.
Click the Volume button, you can set each overlay video volume.