Show HN: Aqueous Archive Format

Aqueous is an archive format and an archiver, aqr, built around lossless recompression. Most files people keep are already compressed, by encoders far weaker than what a modern machine can afford: JPEG's and MP3's Huffman codes, deflate in PNG, ZIP, PDF and gzip, LZ4 and Snappy in browser profiles and databases. Aqueous undoes that compression, codes the contents with stronger models, and rebuilds the original files bit for bit on extraction.

The format is specified in spec/index.bs (an Editor's Draft, not yet fixed). Aqueous is dedicated to the public domain, or under MIT-0 where that is not possible (LICENSE.txt); see CREDITS.md for the projects its ideas come from.

Matt Mahoney's 10 GB benchmark (79,431 files, 10.00 GB), on an Apple M4 (10 cores), 2026-10-27, at commit d84deff:

Compression includes the round-trip check of every file. Some formats alone, as archive / input against zstd -3 of the same files:

The 10 GB archive includes its decoder modules. The figures by format are tentative: they were measured before the modules were embedded in archives. How they were measured, and the formats taken or not yet taken, are in docs/file-formats.md.

cargo build -r -p aqr target/release/aqr -c -o out.aqr some/directory # compress target/release/aqr -t out.aqr # test target/release/aqr -d out.aqr # extract

The workspace's tests are slow in debug builds; run them with cargo test -r.