Plus, at 96+ kbps (assuming an Apple-quality AAC-LC encoder) Opus loses its quality advantage. So at higher bitrates, the benefit of choosing Opus is that encoders/decoders are royalty-free.
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Am I reading that chart wrong? I see Opus ahead across every bitrate.
The evaluation tools used are helpful for encoder development, but at best they're imperfect proxies for human perception, and their predictions are often inconsistent with the human experience. I assume that statements like "apparently the best AAC encoder" aren't meant to be taken too seriously, since everybody who does this stuff knows that ABX/MUSHRA tests with real humans is what tells the tale.
On Opus vs. AAC specifically, there's a long history of studies like https://www.researchgate.net/publication/301428302_Perceived... to help answer that question. (There are interesting charts at the top of page 1175.)
That paper was published in 2014. The reference Opus encoder has certainly had a number of improvements that affect sound quality since then, whereas very few AAC implementations have.
> The reference Opus encoder has certainly had a number of improvements that affect sound quality since then…
Yes, but not for high-bitrate music applications.¹ For example, Opus 1.2 really improved the quality of music encoding at 32–48 kbps. Opus doesn't have to be great at everything to be great at what it does, just like AAC-LC doesn't have to be. (¹Opus 1.6's experimental Opus HD looks very promising for this!)
Apple's and Fraunhofer's closed-source AAC-LC encoders have seen regular, minor quality tuning, and they benefit from the research and engineering work that have been done for the AAC family of encoders (HE-AAC for bitrates down to ~48 kbps, HE-AAC v2 to 32 kbps, xHE-AAC below that).
>So at higher bitrates, the benefit of choosing Opus is that encoders/decoders are royalty-free.
Not only is the new AAC Encoder also royalty-free, the AAC-LC codec itself has been declared by Redhat as patent free ( all patent expired ).