Brotli

Brotli is an open source data compression library developed by Jyrki Alakuijala and Zoltán Szabadka. Brotli is based on a modern variant of the LZ77 algorithm, Huffman coding and 2nd order context modeling.

It can be used to speed up browsing the Web in Chrome, Opera or Firefox. Like zopfli, another compression algorithm from Google, brotli is named after a Swiss bakery product, brötli.

Brotli was first released in 2015 for off-line compression of web fonts. The version of Brotli released in September 2015 by the Google software engineers contained enhancements in generic lossless data compression, with particular emphasis on use for HTTP compression. The encoder was partly rewritten, with the result that the compression ratio improved, both the encoder and the decoder have been sped up, the streaming API was improved, more compression quality levels have been added. Additionally, the new release shows performance improvements across platforms, with decoding memory reduction.

Unlike most general purpose compression algorithms, Brotli uses a pre-defined 120 kilobyte dictionary. The dictionary contains over 13000 common words, phrases and other substrings derived from a large corpus of text and HTML documents. A pre-defined dictionary can give a compression density boost for short data files.

Replacing deflate with brotli typically gives an increase of 20% in compression density for text files, while compression and decompression speeds are roughly unchanged. Streams compressed with Brotli have the content encoding type "br".

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