Hi IELL1,
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The answer to both your questions is that it cannot be done within OpenLP. However there is a work around using either the "Show Desktop" or setting a transparent background for a theme (this will not currently work with Mac's )
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You can place a second program on the desktop that the projector uses such as VLC or a web browser and que up the video. Then simply click "Show Desktop" or set the theme with the transparent background to default.