One of the nice thing about this email chain is that a webp poc is shared by Apple Product Security Team to Google, which I also added into ELEGANTBOUNCER repository and unit tests. Upon reading the code lengths, a specific prefix code is generated for each symbol type (A, R, G, B, distance) based on their respective alphabet sizes which depends of the color cache bits. For color_cache_bits == 6 , the size fo the Green channel huffman table buffer is 718 instead of 654 (for color_cache_bits == 0 ), while the other ones (A, R, B) and the distance code remain constant: