OK, who's been using w3c schools in place of documentation?

:trollface: http://www.w3schools.com/tags/tag_video.asp

```
<video width="320" height="240" controls>
  <source src="movie.mp4" type="video/mp4">
  <source src="movie.ogg" type="video/ogg">
  Your browser does not support the video tag.
</video>
```

Make the error message _slightly_ more actionable to a potentially non-technical reader.