If you read the Wix VideoPlayer API that you linked, you would have found your answer already.
src
Sets or gets the file location of the current video.
Description
Setting the src property changes the displayed video to the video found at the new src value.
Getting the src property returns the location of the current video file.
The video file is one of the following:
-
A video from the Media Manager. URL Format: wix:video://v1/<video_uri>/#posterUri=<poster_uri>&posterWidth=&posterHeight=
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A video from a video sharing site. URL Format: https://www.site.com/video-path
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An external video URL. URL Format: http(s)://site.com/video-file.mp4
If you have outside videos used then you would have already had the external url address.
If you have used videos from your Media Manager, then simply get the url address for the specific video or picture there.