Don't allow next button to be active until all of embedded video is watched

It is possible with videos hosted on Vimeo or YouTube, or similar platforms that share access to their API. You would have to create an index.html that will hold the embedded link and a few lines of JavaScript that sets up connection to API, and a function that would change the SL variable value when the video ends. This index.html is then imported in to Storyline as a web object. Basically, the state of the next button is set to Normal when Variable changes, and the variable is changed when the video ends (a function inside index.html). Downsides: the index.html folder needs to be renamed every time if there is a change and imported again through the web object edit option. Testing this feature all together requires publishing to Review or LMS. If you are interested in this solution I will upload an example and assist you in setting this up.