How to sync video audio with the seekbar controls?

The most accurate method is to start a new slide when the video starts and ends. That way you can avoid the video seekbar altogether.  The slide seekbar, which controls all the objects on the slide, will be in synch with the video.

Simple, easy, and guaranteed, unless the learner clicks on the video, which will freeze the video without stopping the timeline.  Like Alyssa suggested, you can put a transparent (not invisible) shape over the video to prevent clicking. It must have a fill and be set to transparent to function.

But I think you are asking how to keep everything together if the learner scrubs the seekbar, and not using the video seekbar is the only practical method of doing that.