Repacks are made with UHARC because even though it's 15 years old, it still compresses better than 7z/RAR for certain types of media while not being insanely slow like PAQ. The other reply was nonsense so I'll give you a real answer. If you want to play with this concept, look at a tool like precomp : When you decompress the archive, the decompression has to unpack those 500 KB into the uncompressed 4000 KB picture and then the filter uses the compression parameters it detected to recreate the PNG image identical to how it was originally stored inside that big 10 GB file. so the uncompressable PNG image was shrunk from 800 KB to 500 KB.
The compressor can then use a much stronger compression method to shrink the uncompressed picture to fewer bytes.įor example, let's say a 800 KB PNG image is detected and decompressed into a 4000 KB uncompressed picture and then the compressor can compress those 4000 KB into 500 KB. Then, the filter determines what options were used to compress the PNG image and decompresses that png image to an uncompressed picture.
So a smart filter can look through that 10 GB file and detect that at some point in that big 10 GB file a chunk of bytes is compressed with deflate algorithm. PNG images are compressed using deflate algorithm, they're basically zip archives, so they wouldn't compress well. Repacks often use "filters" which are smart enough to look into binary files and detect various file formats within those big binary files, or detect various compression methods.įor example, let's say inside a big 10 GB file of the game there may be a bunch of game textures stored as PNG images. For example, ppm is good for stuff like a pure text story where a dictionary of words can be built, lz78 is a variation of what zip uses, finding sequences of bytes that repeat in a file, lzp is more optimized for very fast decoding, rle is very good for compressing very long sequences of the same byte. The compressor has different algorithms to compress things, and these algorithms are optimized and work much better for specific things. No, you won't compress regular video and music files, these are already compressed by the audio and video codecs used.
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