Monkey's Audio is an algorithm and file format for lossless audio data compression. Lossless data compression does not discard data during the process of encoding, unlike lossy compression methods such as AAC, MP3, Vorbis and Musepack.
Data file compression is employed in order to reduce bandwidth, file transfer time, or storage requirements. A digital recording (such as a CD) encoded to the Monkey's Audio format can be decompressed into an identical copy of the original audio data. Similar to the FLAC and Apple Lossless format, files encoded to Monkey's Audio are typically reduced to about half of the original size, with data transfer rates and bandwidth requirements being reduced accordingly.
Monkey's Audio's advantages are better compression rates compared to FLAC and WavPack, as well as multithreading/multicore support. Monkey's Audio main drawbacks are the fact that it employs a symmetric algorithm, meaning the decoding takes comparable resources to encode, which makes it unsuitable for all but the fastest portable players (via Rockbox firmware), and that it has limited support on software platforms other than Windows; on other platforms only decoding is officially supported by third-party programs. Although the original source code is freely available, the license is not considered to be open source. A GPL version of the decoder has been independently written for Rockbox and then included in ffmpeg.
Monkey's Audio files use the filename extension .ape for audio, and .apl for track metadata.
Like any lossless compression scheme, Monkey's Audio format takes up several times as much space as lossy compression formats like AAC, MP3, and Vorbis. A Monkey's Audio file is 3–5 times as large as a 192 kbit/s bitrate MP3 file.
The Shorten format, popular with live taping enthusiasts for years, is no longer in development but is still in use on some sites such as etree. FLAC has an active development community that continues to refine the format. Because Monkey's Audio is relatively slow when encoding or decoding files (what FLAC accomplishes in several seconds can take a minute or more with Monkey's Audio) FLAC has largely eclipsed it as the preferred format for commercial distribution of lossless audio.
Although Monkey's Audio is distributed as freeware, the source code includes license terms that prevent most Linux distributions and other free software projects from including it. In contrast, FLAC has only open source licenses, so it comes pre-installed with most Linux distributions, is preferred by Linux users, and enjoys broad support in applications.