It looks like we are slightly talking past each other.
I was interested in differences in resulting storage file sizes.
For lossless flac, that will most certainly depend on the (0-8) setting. I am sure you didn't intend arguing that?
No, that's exactly right. FLAC 0 -> 8 adjusts the target bitrate on a downward scale as shown in my images, which affects the file size also on a downward scale.
I have always been convinced that different lossy algorithms would perform differently in resulting file sizes depending on how sophisticated or advanced they are.
I did some quick testing with dBpoweramp, which has the option to refine any fixed cbr setting to 10 different quality levels.
I always assumed that higher quality settings would not only (substantially) increase the encoding time, but it also would result in larger file sizes, since more refined audio information would need to be stored.
It also has the option to select e.g. 'stereo' encoding vs. 'joint-stereo' encoding.
Again, I have always assumed and understood that 'stereo' would take up more storage space then encoding 'joint-stereo'.
But trying out these different settings (with the same 320cbr setting) indeed always results in the same file size.
That's really surprising to me. So I'll probably need to re-adjust my understanding on this matter.
I encode video and audio all day every day pretty much. File Size will always equal bit rate per second times seconds. Always. For CBR, it's easy to do the math, because each frame is encoded with the same bit rate (320 for example). For VBR, there is no fixed bit rate because it's variable on each frame - silence in audio is encoded with 0 bits for example - so you can't ever know the exact size of the the resulting file, but you can estimate based on the target bit rate.
Quality settings in encoders have to do with how
they get to the bit rate in question. They may futz this or that set of frequencies differently, rolling off above or below a certain frequency, or use one channel to cancel out what's in another channel so it's not encoded twice. But they can't affect the underlying math, which is always File Size = bits per second * seconds. That is a mathematical constant.
But to return on-topic: I was responding to the notion that some users would use Opus also at higher bit-rates, because it would result in lower file-sizes than mp3, with comparable (or even better) sound-quality.
And on that, I have not found any reliable proof or abx testing.
I'm with you there. I've found no reason to use any lossy compression besides MP3. They may get better quality at low bit rates, and that may please some people who value storage space over all else, or maybe if you're encoding audio books where you're looking at really low bit rates and not all that concerned about quality, but, for music, V0 MP3 will serve you well as it has served everyone else well for a very long time now.