Do videos play within Yarno?

The short answer is, yes! 

If the video is hosted on YouTube or Vimeo, then when a learner clicks on it in an Explanation, the video will open within Yarno. 

See How do I add video into Yarno? for step by step instructions. 

If the video is hosted on a different provider, say Wistia, then the video will open within a new browser tab. Once the learner has watched the video, they'd need to close that tab and return to Yarno.