This isn’t necessarily a finished product but does seem to work well. It is particularly nice if you are using a screen reader and browser that support ARIA live updating. This is a technology that allows web page changes to be announced automatically to the screen reading user.
The accessible interface to YouTube can be accessed at http://tube.majestyc.net/. As an example in this version, ARIA live updates are used to announce video states such as buffering, playing and paused.
This is a research project so the developer is looking for feedback. Consider dropping by the page and completing a short questionnaire.