What I mean is, they are the potential limitations:
1. Modern VoIP applications are incompatible with Windows 95/98
2. Hardware availability
3. Networking issues
4. Driver support
5. Obsolete Protocols
6. Performance limitations (indeed, modern audio codecs may be an issue, incl. Opus and AAC)
A 250 MHz processor can handle basic voice chat but with significant limitations, and there is much more to it when it comes to practice... so while technically a 250 MHz processor might (for historical experimentation or nostalgia), in reality it is not practical for functional use today.
A Pentium 233MMX is capable of DVD playback, so I think voice chat is definitely possible. I've worked on VoIP phones that had slower CPUs and they handled a SIP stack just fine.
A Pentium III 733MHz with 128MB RAM running Win98 works fine for (low-res) video chat. Been there, done that.
No they aren't. DVD playback on early systems was hardware based using an MPEG2 decoder (often included on the sound card that came packed in with the DVD drive, or on some video cards or dedicated MPEG decoder cards)
Software playback of DVD's on a Pentium MMX at 233mhz is going to be limited to single digit framerates, especially if you are trying to decode Dolby Digital or DTS audio as well
I know, but it is still not practical or suitable for functional use. Just to help you understand what I mean: obtaining such a CPU (with the rest of the compatible hardware) and obtain & install Windows 98 is not as straightforward these days. Sure it may be for me because I still have my old hardware, but still. And by the way (for another PC) I had to install Windows 11 because I had Windows 7 and all my programs stopped supporting it. Not practical either, sadly. I was forced to install Windows 11.
I doubt they are using exponential time algorithms. They appear to be using Opus, which appears to be O(NlogN) worst case. Opus is also well known to be computationally cheap, like most (all?) audio codecs. It should run fine on the Pentium II.
I would be more concerned about modern video codecs. None of them are exponential time, but they need so much compute that it is unlikely that a Pentium II could handle them.
I'm not sure if Discord has options to fall back to H.263 like the open standards world (SIP) does, but that's the classic codec from 1995 and would definitely be usable on the CPUs of the time; if that's still too slow, then there's always H.261 (1988) which is basically "motion JPEG but with interframes".
I’m pretty sure they didn’t mean “exponentially more” in the asymptotic complexity sense. They could be both O(N log(N)), but with dramatically different constants.