I'm not sure what exactly you mean by "an evolving standard".
That seems an oxymoron if ever I heard one. Either it's a standard,
or it's an evolving system. It can't be both.

To the best of my understanding, all audio and video codecs carry with them
the information need to correctly decode the transmission. This allows (for
example) DVDs and Blu-rays to use varying bitrates and different codecs. (If
this isn't right, please correct me.)