Following on from an issue (#1446) regarding some errors in an example, it seems the intention of the creator of the example was to attach a video property to a MusicGroup type, to link to a video of the group in question.
As the domainIncludes of video is only CreativeWork this is not possible.
We could propose extending the domain to include MusicGroup but that would only address a simple symptom of a potentially broader problem.
In this age of Snapchat, YouTube, etc., etc., there is a blurring of boundaries between what is an image or a video (moving) image. How do we classify an IPhone Live Photo for example?
In the current Schema.org structure any Thing can have an image. Is it time to say that say any Thing can also have a video image?
This could be addressed either by changing the domain of video from CreativeWork to Thing, or adding VideoObject to the range of image.
This overlaps with issue #292 (something I'd really like to see resolved). The original request/discussion was also about expanding the domain of video to schema.org/Thing.
On the blurred lines front, we could also decide 'video' is a special case (subproperty) of 'image', i.e. image(s) that move.
Sorry to be nitpicky but I don't see a video as images that move. At best it's an collection of images that should be watched in a specific order (at a certain speed).
Now I understand the reluctance to keep adding new properties to schema.org/Thing but given the fact video plays such an important role on the web nowadays and that you can find videos about any type of thing, wouldn't it just be easiest to add video to schema.org/Thing.
It would actually resolve some of the real world issues webmasters have.