The simplest way seems to be to use the slide timeline. Start the video when the slide starts, and the slide timeline will be the same as the video. Place a filled shape with 98% transparency above the slide so the learner doesn't click the video to stop it. That way, when the slide timeline reaches a point, the video is at the same point. When they jump to a URL,lightbox it. The slide will pause, and resume from that spot when the lightbox is closed.
If you want the learner to be able to pause the video, allow them to pause the slide timeline, which now controls the video.
