Ben Crystal does Shakespeare in his Voice

I cannot imagine that anyone has had access to an actual sound recording of Shakespeare's voice, so the question is How does actor Ben Crystal, or anyone for that matter, know what his accent was?  My guess is that we infer from his writing, maybe from the Folio, and his poetry in particular.  In any case, I found this little bit of instruction informative and enjoyable, and I marvel at how verse and versatile actors have to be to perform Shakespeare.