Both, primarily the first. Low latency is definitely a requirement, but no issues with Opus on that account.

> I haven't looked into how expensive it is to encode in terms of CPU time, so I assume maybe you're taking about a bottleneck in terms of the number of simultaneous streams you can support on a single CPU?

Yup! I work on https://vircadia.com/ -- we have to compress audio in real time and every user gets their own mix since it depends on their location in 3D space. It turns out to add up pretty fast, and you can't fit that many people into a cheap VPS.

That's why I'm working on FLAC support for it. If bandwidth is plentiful but CPU resources are lacking it's a good alternative to have.

This code originally came from the High Fidelity company, which made their own codec. It's some piece of black magic that cuts down audio by exactly 1/4th and is amazingly fast. But it's closed source.

There's no way their proprietary codec is less black magic than Opus is. I've rarely if ever seen a closed source codec designed by people who really know what they're doing; they're usually just whatever the cowboy they hired thought would be cool. It's not like management is going to be able to tell if it's state of the art or not.

Well, I say "black magic" because at least to me it's a quite mysterious creation. But I'm no audio engineer.

It's a lossy codec that's for some reason fixed rate, and shrinks audio by exactly 1/4th. The resulting quality is very good (works perfectly fine for music), and it's much faster than Opus. It retains stereo and high frequencies and sounds just fine. I'm sure there's a tradeoff somewhere, but it's certainly good enough to hold music events without people complaining.

I think it might be possibly related to codecs like AptX.

So far I've not found anything competitive that we could use -- stuff is either closed, or far more CPU intensive.

Yeah, it sounds like ADPCM with a fixed ratio like that. It's extremely simple and adds no latency, which are both good for streaming.

Usually a fixed compression ratio is a terrible tradeoff, but for streaming it kind-of makes sense.

I don't think it's ADPCM since it sounds really good. I'm not an audiophile or have done any comprehensive testing, but it' the kind of quality a normal person would use for music without complaining.

That was meant to agree with you - AptX is a kind of ADPCM with some other filters added on, so this could be the same thing. That's how it gets low latency.