It is usually a good idea to disable the Next button until a require activity has been completed. You know your users can't complete the activity in less than 15 seconds. I will propose then to disable the next button for 15 seconds. Write on the disabled button a message like "watch instruction first".


Provide two (equal-weight) buttons: "Straps fitted OK" and "Show me how". Then you have no tempting "Next" button and new users are made aware that the video is relevant.

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