SL 360 - Zoom Regions in Video

The Zoom Region feature is especially helpful in software demonstrations, since the "base video" is usually full-screen, and the on-screen text can be daunting to read without magnification.

Using Storyline 360's Screen Capture feature, I can play and pause the resultant video and easily insert Zoom Regions as needed.

However, I'm going to have to work with an MP4 video -- a screen recording done by a client.

When I insert the MP4 in Storyline 360, I can play the video on-screen, but when I come to a point where I want to add a Zoom Region and click pause, the on-screen view reverts to the beginning of the video, while the playhead remains at the point at which I paused. When clicking play again, the video starts at the beginning instead of resuming from the position of the playhead.

Obviously, this scenario makes it hard (impossible??) to add Zoom Regions to imported MP4 videos.

So, what's the difference between video captured by Storyline and an MP4 video? Is there a solution?