WavPack
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| WavPack | |
|---|---|
| Developed by | David Bryant |
| Latest release | 4.41 / May 6, 2007 |
| OS | Cross-platform |
| Genre | Audio codec Encoder |
| License | BSD license |
| Website | www.wavpack.com |
| WavPack | |
|---|---|
| File name extension | |
| Developed by | David Bryant |
| Type of format | Audio |
WavPack is a free, open source lossless audio compression format developed by David Bryant.
Contents |
[edit] Features
WavPack compression (.WV files) can compress (and restore) 8, 16, 24 & 32-bit float audio files in the .WAV file format. It also supports surround sound streams and high frequency sampling rates. Like other lossless compression schemes the data reduction rate varies with the source, but it is generally between 30% and 70% for typical popular music and somewhat better than that for classical music and other sources with greater dynamic range.[citation needed]
WavPack also incorporates a "hybrid" mode which still provides the features of lossless compression, but creates two files: A relatively small, high-quality lossy file(.wv) that can be used by itself, and a "correction" file(.wvc) that (when combined with the lossy file) provides full lossless restoration. This allows the use of lossy and lossless codecs together. This "hybrid" feature is also offered by OptimFROG DualStream.
[edit] Summary
- Open source, released under a BSD-like license
- Multiplatform
- Error robustness
- Streaming support
- Supports multichannel audio and high resolutions
- Hybrid/lossy mode
- Hardware support
- Tagging support (ID3v1, APE tags)
- Supports RIFF chunks
- Replay Gain compatible
- Ability to create self extracting files for Win32 platform
- Supports 32bit float streams
- Supports embedded CUE sheets
- Includes MD5 hashes for quick integrity checking
- Can encode in both symmetrical and asymmetrical (=slower encoding to speed up decoding) modes.
[edit] History
David Bryant started development on WavPack in mid-1998, with the release of version 1.0. This first version compressed and decompressed audio losslessly, but by then it had already featured one of the best efficiency vs. speed ratio among lossless encoders.[citation needed]
Very soon after the release of version 1.0, v. 2.0 was released, featuring lossy encoding (using only quantization of prediction residue for data reduction - no psychoacoustic masking model was applied to the stream).
In 1999 version 3.0 was released, with a new "fast mode" (albeit with reduced compression ratio), compression of raw (headerless) PCM audio files, and error detection using a 32-bit cyclic redundancy check.
WavPack development is ongoing.[citation needed] A feature added in late 3.x versions is the hybrid mode, where the encoder generates a lossy file and a correction file, so that both can be decompressed back to a PCM stream of slightly less quality than the original.[citation needed]
The current release, as of May 2008, is version 4.4. [1]
A "roadmap" is also published by the author, containing possible hints on future development. [2]
[edit] Support
[edit] Software
Some software supports the format natively, while others require plugins. The official WavPack website offers plugins for Winamp, Nero Burning ROM, and several other applications, as well as a DirectShow filter.[1]
[edit] Hardware
WavPack is supported by hardware media players that run the open source Rockbox firmware, such as iriver H100 series, H300 series, iPod (Video, Color, Photo, Nano) and more.[2] The WavPack website also includes a plugin that allows support for the format on the Roku PhotoBridge HD.[1]
[edit] Technology
To ensure high-speed operation, WavPack uses a predictor that is implemented entirely in integer math.[citation needed] In its "fast" mode the prediction is simply the arithmetic extrapolation of the previous two samples. For example, if the previous two samples were -10 and 20, then the prediction would be 50. For the default mode a simple adaptive factor is added to weigh the influence of the earlier sample on the prediction. In our example the resulting prediction could then vary between 20 for no influence to 50 for full influence. This weight factor is constantly updated based on the audio data's changing spectral characteristics.
The prediction generated is then subtracted from the actual sample to be encoded to generate the error value. In mono mode this value is sent directly to the coder. However, stereo signals tend to have some correlation between the two channels that can be further exploited.[citation needed] Therefore, two error values are calculated that represent the difference and average of the left and right error values. In the "fast" mode of operation these two new values are simply sent to the coder instead of the left and right values. In the default mode, the difference value is always sent to the coder along with one of the other three values (average, left, or right). An adaptive algorithm continuously determines the most efficient of the three to send based on the changing balance of the channels.
Instead of Rice coding, a special data encoder for WavPack is used. Rice coding is the optimal bit coding for this type of data, and WavPack's encoder is less efficient, but only by about 0.15 bits/sample (or less than 1% for 16-bit data). However, there are some advantages in exchange; the first one is that WavPack's encoder does not require the data to be buffered ahead of encoding, instead it converts each sample directly to bitcodes. This is more computationally efficient and it is better in some applications where coding delay is critical. The second advantage is that it is easily adaptable to lossy encoding because all significant bits (except the implied "one" MSB) are transmitted directly. In this way it is possible to only transmit, for example, the 3 most significant bits (with sign) of each sample. In fact, it is possible to transmit only the sign and implied MSB for each sample with an average of only 3.65 bits/sample.
This coding scheme is used to implement the "lossy" mode of WavPack. In the "fast" mode the output of the non-adaptive decorrelator is simply rounded to the nearest codable value for the specified number of bits. In the default mode the adaptive decorrelator is used (which reduces the average noise about 1 dB) and both the current and the next sample are considered in choosing the better of the two available codes (which reduces noise another 1 dB).
No floating-point arithmetic is used in WavPack's data path because, according to the author, integer operations are less susceptible to subtle chip-to-chip variations that could corrupt the lossless nature of the compression,[citation needed] the Pentium floating point bug being an example. It is possible that a lossless compressor that used floating-point math could generate different output when running on that faulty Pentium.[citation needed] Even disregarding actual bugs, floating-point math is complicated enough that there could be subtle differences between "correct" implementations that could cause trouble for this type of application.[citation needed] A 32-bit error detection code to the generated streams is included to maintain user confidence in the integrity of WavPack's compression.[citation needed]
WavPack source code is portable, and has been compiled on several Unix and Unix-like operating systems (Linux, Mac OS X, Solaris, FreeBSD, OpenBSD, NetBSD, Compaq Tru64, HP-UX...) as well as Windows, DOS, Palm OS, and OpenVMS. It works on many architectures, including x86, ARM, PowerPC, AMD64, IA-64, SPARC, DEC Alpha, PA-RISC, MIPS and Motorola 68k.
WavPack support was added to WinZip starting with version 11.0 beta, released in October 2006.[3] This extension to the ZIP file format was included by PKWARE, the maintainers of the format, in the official APPNOTE.TXT description file starting with version 6.3.2, released on September 28, 2007.[4]
[edit] References
- ^ a b WavPack downloads.
- ^ Sound Codecs, Rockbox Wiki.
- ^ WinZip - Additional Compression Methods Specification. WinZip International LLC (2006-11-15). Retrieved on 2008-01-06.
- ^ APPNOTE.TXT - .ZIP File Format Specification. PKWARE Inc (2007-09-28). Retrieved on 2008-01-06.
[edit] See also
[edit] External links
- Official website
- WavPack forum at Hydrogenaudio Forums
- Historical versions at ReallyRareWares
- A comparison of several Lossless Audio encoders at Hydrogenaudio Wiki.
- WavPack on MultimediaWiki
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