Automatic pauses of video for a pop-up quiz

If the video doesn't have its own seekbar, and starts when the slide starts, you can Show layer XX when the timeline of the slide reaches YY seconds. If the layer is set to pause the timeline of the base, the video will pause while the layer is showing.

On the other hand, personally, I welcome the freedom and flexibility that come from breaking videos into manageable chunks, even if I don't need quizzes in them. In the space between slides, I can bring in other opportunities and enhancements, travel to optionally other slides, and always return to the next spot. There are any number of readily available free editors that can load, split and save a video in less time than it takes to fool around trying to stop it and build a question and response without having to protect the timeline. Of course, if you don't care how long it takes or how difficult it is, you can always try to crop it in SL. ) FWIW