I don't know much about the practical engineering of modern codecs, I was just assuming that the exact order and combination of operations (particularly roundin

I don't know much about the practical engineering of modern codecs, I was just assuming that the exact order and combination of operations (particularly rounding) would be underspecified to allow for different architectures, and that would impact at least the low bits of the output. magicalhippo's comment suggests this might not actually be the case for H.264, which does also have a lossless mode... There's another more important point, though: Modern lossy codecs are designed to be perceptually transparent, rather than minimizing an absolute signal error. The difference is a likely a large and unpredictable signal, so the typical Rice coding will be ineffective for compressing the residual. Wavelets still might be interesting as a basis, there's at least one project [1] that reports comparable ratios to FLAC, if a bit lower. [1] https://shamazmazum.github.io/wavelet-audio/ https://shamazmazum.github.io/wavelet-audio/