According to several online sources, at a public reading of Megillat Esther it is preferable that one should follow along silently from a kosher scroll, so that if you miss hearing a word you will nevertheless have fulfilled the mitzvah of reading the entire Megillah from a scroll.
This seems to imply that the hearing of the Megillah is not the essence of the mitzvah -- and indeed the same sources linked above all say that the real mitzvah is to read the megillah.
So my question: if one is, for reasons of health or other complicating factors, unable to attend a public megillah reading, so is going to read it privately at home, from a kosher scroll -- does that reading need to be done out loud, or is a silent reading sufficient?
(A related question is at Would somebody be yotze the Megillah reading by watching it LIVE STREAMING while following from a Kosher Megillah?, but that question has no answers, and adds the complicating additional factor of listening to a live stream while simultaneously following along silently. Which, to be honest, I am also interested in -- but I would like to separate out the two issues of "reading silently" and "listening to a livestream", which I think each raise separate questions.)