How to ensure a video is watched before a response can be made

I'm presenting a series of short (2 seconds each) videos that participants have to watch, then select a response from a field of 4 choices. I want to ensure that subjects are actually watching the videos before making their choices and not just making their selections at random without watching.
I've tried including a timing question so that the next button isn't displayed until after the duration of the video. However, since I'm randomizing the order of video presentation, this doesn't work.
Is there any way to verify that the video was watched before allowing a response or moving to the next question?