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You can also make ZIP files smaller by switching the compression from Deflate to Zstandard. In the one case I tried this, this resulted in a 60% file size decrease [1]. Unfortunately Info-ZIP which provides the unzip command hasn't had a release in 18 years, so it doesn't support this newer compression/decompression method. You have to use 7-Zip instead.

[1] https://github.com/UKGovernmentBEIS/inspect_ai/pull/3145

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What is the open standard?

As far as I know, the ISO standard for zip only specifies two compression methods: "store" (no compression) and "deflate". If I follow that, when I create a zip file, I know it's not performant, but at least it's almost universal (except for file ownership, permissions, character encoding and anything modern).

The corporate PKWARE has added other compressions to their original zip software, but those are not in the standard. They will not work for an EPUB, a LibreOffice file, etc. If I want a good compression, I reach for zstd (often through `tar`) or 7z if I want more portability.

Then it's not a zip file anymore.

Just like if you modified PNG files to use zstandard instead of deflate, but otherwise be identical, it's still not a PNG file anymore.

That's not true. Zip files have supported other compression algorithms since the late 90s.

I guess its PNG v2 then? ;)

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