I heard here on the forum of "weak" demonstrative. The way I understand that, is that they are only considered as demonstrative when it's impossible for them to be personal pronouns.
In other terms, each time they can be personal pronouns, they are.
If they are next to a noun, they are naturally more susceptible to be pronouns, (forming a couple demonstrative-noun)
Here they are next to a verb, and no nouns.
It's the way I understood that, I expect more info from a more advanced user than me.
I'm pretty sure you also can have a file at any speed with human-generated audio, with an algorithm. The only thing is that they didn't planned it. I noticed a lot of "slow down" button, and stuff disappears when they revamped the site, complaining that it was too heavy on their servers.
Yes, it's totally acceptable to use either "is" or "ille", to mean "he".
"Is" is the personal pronoun: In reality, there is no real personal pronoun to mean the 3rd person in Latin, there is only demonstrative weaker than the others, and "is" is the weakest, so the closer from a modern "he".
So, in Latin, the demonstrative "ille" (masculine "that") can be also used as a personal pronoun (here it's masculine, so it's "he"). It's weird for us, but it's the way it is, and we have only to learn it, and apply it, without trying to understand too much. I think the "he" meaning for the masculine "that" is a bit like saying "the latter is..." which is, in my opinion, the historical etymology of the personal pronoun, how they entered the Human language.
As I said, "is" is closer from a personal pronoun than "ille" (but "ille" is still right), and it brings different connotations.
But don't ask me what is the subtile difference in the meaning between "is" and "ille" when they mean "he", at my little level, I just use them to mean "he", but maybe a very advanced user could explain it.
Is means this or that masculine person or thing; iste means that masculine person or thing near you, or perhaps which you have just mentioned; ille means that masculine person or thing over there. Iste is sometimes used disparagingly. Hic means this masculine person or thing. Hic, haec, hoc are masculine, feminine and neuter respectively. Same goes for is, ea, id, and iste, ista, istud, and ille, illa, illud.