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When audio files are to be processed, either by further compression or for editing, it is desirable to work from an unchanged original (uncompressed or losslessly compressed). Processing of a lossily compressed file for some purpose usually produces a final result inferior to the creation of the same compressed file from an uncompressed original.
This means that compressed archives with the UC2 file extension can hold almost 1 million files. .uca PerfectCompress [17] Windows: Windows: No Based on PAQ, RZM, CSC, CCM, and 7zip. The format consists of a PAQ, RZM, CSC, or CCM compressed file and a manifest with compression settings stored in a 7z archive. .uha UHarc DOS/Windows: DOS/Windows ...
Executable compression can be used to prevent direct disassembly, mask string literals and modify signatures. Although this does not eliminate the chance of reverse engineering, it can make the process more costly. A compressed executable requires less storage space in the file system, thus less time to transfer data from the file system into ...
Files can be returned to their original state using uncompress. The usual action of uncompress is not merely to create an uncompressed copy of the file, but also to restore the timestamp and other attributes of the compressed file. For files produced by compress on other systems, uncompress supports 9- to 16-bit compression.
Even binary data files can be compressed with this method; file format specifications often dictate repeated bytes in files as padding space. However, newer compression methods such as DEFLATE often use LZ77-based algorithms, a generalization of run-length encoding that can take advantage of runs of strings of characters (such as BWWBWWBWWBWW).
Thus, a representation that compresses the storage size of a file from 10 MB to 2 MB yields a space saving of 1 - 2/10 = 0.8, often notated as a percentage, 80%. For signals of indefinite size, such as streaming audio and video, the compression ratio is defined in terms of uncompressed and compressed data rates instead of data sizes:
Compressed file formats often feature both compression (storing the data in a small space) and archiving (storing multiple files and metadata in a single file). One can combine these in two natural ways: compress the individual files, and then archive into a single file; archive into a single data block, and then compress.
In fact, if we consider files of length N, if all files were equally probable, then for any lossless compression that reduces the size of some file, the expected length of a compressed file (averaged over all possible files of length N) must necessarily be greater than N. [citation needed] So if we know nothing about the properties of the data ...