I’m not sure what you mean by “short of DRM”, because YouTube already does what it can to prevent unauthorised clients accessing it. (Have you seen how unreliable “YouTube downloaders” can be, especially for very long videos or in resolutions above HD?) But ultimately the flaw in any DRM-style solution is that the end result still needs to be able to be played back on client-controlled systems, and that is always going to provide an avenue for exploitation. It can’t be avoided.