We typically do this using custom code, so we have maximum control over the player. Build a mutationobserver to watch the lightbox, when it becomes visible, start the video, when it becomes invisible, pause the video.
You might also be able to accomplish a crude version of this by modifying the video URL to include autoplay and mute. Typically autoplay won’t work without mute. Note you might need to switch to an HTML embed to control the URL more completely, which would require you to use a different lightbox solution like fancybox.