ffmpeg developer: "Using <extremely common use case> is invalid to prove anything." Why do I even waste my time on this?https://twitter.com/BMahol/status/1255867904475750401 …
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I wonder if a randomized comparison test could be used to quantify psychoacoustic loss? Basically, at a given bitrate, what percentage of human listeners can correctly identify the compressed vs. uncompressed sample side by side?
Yes, this is how codec tests are done, but 1) I'm not going to recruit a team of volunteer testers just to prove this to the ffmpeg devs, and 2) it only works to determine transparency thresholds. Comparisons between encoders at non-transparent bitrates are always subjective.
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The latter is important because *how audible/annoying/disagreeable* your artifacts are is a huge part of being a good psychoacoustic encoder. Opus is notoriously good here, for example.
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Any those are just a few thoughts. Having spent a lot of time with the libav* APIs, I’m not sure I want to wrestle with that code any more than I have to, let alone go to the mat with the minds that conceived it.
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I would think you could set up a small scale test on eg. Mechanical Turk and get data quickly? It wouldn’t be subjective if you can prove that the transparency threshold occurs at a higher bitrate (for a statistically significant number of listeners) in the ffmpeg implementation.
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TBH, given that I was able to easily tell the presence or absence of one round of ffmpeg-aac at 320kbps (on an already transcoded input, but that's irrelevant), which is what started all of this this week, I don't think it *has* a transparency threshold.
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