Sadly, the assumption is false.<p>The EME standard is a standard for a way for scripts on a page to ask the browser to talk to the CDM.  The actual interaction between the browser and the CDM is completely unspecified; it just needs to enable the browser to implement the EME APIs.<p>I think a more apt comparison is that EME is to CDMs more like the 2D canvas API is to graphics libraries.  At least in a world in which graphics libraries had very restrictive licenses and you could require, via the canvas API, a particular graphics library to be used for rendering your canvas.