[gcp]

MPEG2 isn't an audio codec, it's a suite of standards. But based on my experience writing hardware encoders for this use case, you're talking about MPEG1 Layer 2 audio.

Opus outperforms that greatly, but it's not going to outperform MPEG1 Layer 2 at 256kbps while only outputting 64kbps itself. (Will likely need >= 96kbps for that).

[marquis]

Thanks, that was what I was referencing. How well do you think Opus will compare to AAC?

[gcp]

I already posted tests results elsewhere in this topic. It outperforms it at low bitrates. I suspect also at higher ones but once both codecs get imperceptible for most listeners (which is the case for AAC and Opus >128kbps) it's very hard to get statistically significant results.