WavPack
Encyclopedia
WavPack is a free
, open source
lossless audio compression format
developed by David Bryant.
audio files in the .WAV
file format. It also supports surround sound
streams and high frequency sampling rate
s. 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.
A similar "hybrid" feature is also offered by OptimFROG DualStream and MPEG-4 SLS
.
Very soon after the release of version 1.0, v. 2.0 (2 September 1998) 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 (12 September 1999) 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. A feature added in late 3.x versions is the "hybrid" mode where the encoder generates a lossy file and a correction file such that both can be decompressed back to a PCM stream that is same quality as the original. A “roadmap” is also published by the author, containing possible hints on future development.
, Nero Burning ROM
, and several other applications, as well as a DirectShow
filter.
Non-native support:
The WavPack website also includes a plugin that allows support for the format on the Roku PhotoBridge HD.
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. 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, since 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 (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. 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. A 32-bit error detection code to the generated streams is included to maintain user confidence in the integrity of WavPack's compression.
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
, Alpha
, PA-RISC
, MIPS
and Motorola 68k
.
A cut-down version of WavPack was developed for the Texas Instruments TMS320 series Digital Signal Processor. This was aimed predominantly at encouraging manufacturers to incorporate WavPack compression (and de-compression) into portable memory audio recorders. This version supported features that were applicable only to embedded applications (stream compression in real-time, selectable compression rate) and dropped off features that only applied to full computer systems (self extraction, high compression modes, 32-bit floats). The TMS320 series DSPs are native integer devices, and support WavPack well. Some 'special' features of the full WavPack software were included (ability to generate a correction 'file' (stream) for example) and others were excluded. The port was based on version 4.
WavPack support was added to WinZip
starting with version 11.0 beta, released in October 2006. 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 28 September 2007.
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
, open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
lossless audio compression format
File format
A file format is a particular way that information is encoded for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa. There are different kinds of formats for...
developed by David Bryant.
Features
WavPack compression (.WV files) can compress (and restore) 8-, 16-, 24-, and 32-bit fixed-point, and 32-bit floating pointFloating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
audio files in the .WAV
WAV
Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
file format. It also supports surround sound
Surround sound
Surround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...
streams and high frequency sampling rate
Sampling rate
The sampling rate, sample rate, or sampling frequency defines the number of samples per unit of time taken from a continuous signal to make a discrete signal. For time-domain signals, the unit for sampling rate is hertz , sometimes noted as Sa/s...
s. 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.
Hybrid mode
WavPack also incorporates a "hybrid" mode which still provides the features of lossless compression, but it 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.A similar "hybrid" feature is also offered by OptimFROG DualStream and MPEG-4 SLS
MPEG-4 SLS
MPEG-4 SLS, or MPEG-4 Scalable to Lossless as per ISO/IEC 14496-3:2005/Amd 3:2006 , is an extension to the MPEG-4 Part 3 standard to allow lossless audio compression scalable to lossy MPEG-4 General Audio coding methods...
.
Summary
- Open sourceOpen sourceThe term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
, released under a BSD-like license - Multiplatform
- Error robustness
- StreamingStreaming mediaStreaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
support - Supports multichannel audio and high resolutions
- Hybrid/lossy mode
- Hardware support (provided by RockboxRockboxRockbox is a replacement for the standard firmware in various forms of digital audio players . It offers an alternative to the player's operating system, in many cases without removing the original firmware, which provides a plug-in architecture for adding various enhancements and functions...
firmware) - Metadata support (ID3v1ID3ID3 is a metadata container most often used in conjunction with the MP3 audio file format. It allows information such as the title, artist, album, track number, and other information about the file to be stored in the file itself....
, APEAPEv2 tagAn APE tag is a tag used to add metadata, such as the title, artist, or track number, to digital audio files.- APEv1 :The APEv1 tag was designed for the Monkey's Audio format....
tags) - Supports RIFF chunks
- ReplayGain compatible
- Ability to create self extracting files for the Win32 platform
- Supports 32-bit floating point streams
- Supports embedded CUE sheets
- Includes MD5MD5The MD5 Message-Digest Algorithm is a widely used cryptographic hash function that produces a 128-bit hash value. Specified in RFC 1321, MD5 has been employed in a wide variety of security applications, and is also commonly used to check data integrity...
hashes for quick integrity checking - Can encode in both symmetrical and asymmetrical (slower encoding to speed up decoding) modes
History
David Bryant started development on WavPack in mid-1998 with the release of version 1.0 (1998-08-15). This first version compressed and decompressed audio losslessly, but by then it already featured one of the best efficiency vs. speed ratios among lossless encoders.Very soon after the release of version 1.0, v. 2.0 (2 September 1998) 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 (12 September 1999) was released, with a new "fast mode" (albeit with reduced compression ratio), compression of raw (headerless) PCM
Pulse-code modulation
Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...
audio files, and error detection using a 32-bit cyclic redundancy check
Cyclic redundancy check
A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...
.
WavPack development is ongoing. A feature added in late 3.x versions is the "hybrid" mode where the encoder generates a lossy file and a correction file such that both can be decompressed back to a PCM stream that is same quality as the original. A “roadmap” is also published by the author, containing possible hints on future development.
Software
Some software supports the format natively (like Jack! The Knife), while others require plugins. The official WavPack website offers plugins for WinampWinamp
Winamp is a media player for Windows-based PCs and Android devices, written by Nullsoft, now a subsidiary of AOL. It is proprietary freeware/shareware, multi-format, extensible with plug-ins and skins, and is noted for its graphical sound visualization, playlist, and media library features.Winamp...
, Nero Burning ROM
Nero Burning ROM
Nero Multimedia Suite is a popular software suite for Microsoft Windows by Nero AG . Version 10 of this product was released in April 2010.- Included products :The following applications are included in Nero 11 :Disc authoring...
, and several other applications, as well as a DirectShow
DirectShow
DirectShow , codename Quartz, is a multimedia framework and API produced by Microsoft for software developers to perform various operations with media files or streams. It is the replacement for Microsoft's earlier Video for Windows technology...
filter.
Hardware
Native support:- Cowon A3 PMP supports WavPack out of the box.
Non-native support:
- Apple iPodIPodiPod is a line of portable media players created and marketed by Apple Inc. The product line-up currently consists of the hard drive-based iPod Classic, the touchscreen iPod Touch, the compact iPod Nano, and the ultra-compact iPod Shuffle...
range of music players do not support WavPack out of the box, but can through open source RockboxRockboxRockbox is a replacement for the standard firmware in various forms of digital audio players . It offers an alternative to the player's operating system, in many cases without removing the original firmware, which provides a plug-in architecture for adding various enhancements and functions...
firmware. - iriver H100 seriesIriver H100 seriesThe iriver H100 series is a series of discontinued portable digital audio players made by iriver company and originally released in October 2003. The models in the H100 series differ mainly in hard drive storage capacity...
, can through open source Rockbox firmware. - iriver H300 seriesIriver H300 seriesThe iriver H300 series includes two hard-disk-based, multi-codec music jukebox players, the iriver H320 and the iriver H340. Each can play music, transfer pictures directly from digital cameras and UMS-compatible devices, such as flash drives , and display digital images on a colour screen...
, can through open source Rockbox firmware. - Android Devices, Android Smartphones, HTC MagicHTC MagicThe HTC Magic is a smartphone designed and manufactured by HTC Corporation. It is the second HTC device to run the Android software stack, after the HTC Dream. Vodafone unveiled the Magic on February 17, 2009 at the Mobile World Congress in Barcelona...
, Nexus OneNexus OneThe Nexus One was Google's flagship smartphone manufactured by Taiwan's HTC Corporation. It became available on January 5, 2010 and uses the Android open source mobile operating system...
, Motorola DroidMotorola DroidThe Motorola Droid is an Internet and multimedia enabled smartphone designed by Motorola, which runs Google's Android operating system. The Droid had been publicized under the codenames Sholes and Tao and the model number A855...
can with the installation of third party Media Player software such as the freeware Meridian Media Player
The WavPack website also includes a plugin that allows support for the format on the Roku PhotoBridge HD.
Technology
To ensure high-speed operation, WavPack uses a predictor that is implemented entirely in integer math. 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
Stereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
signals tend to have some correlation between the two channels that can be further exploited. 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, since all significant bits (except the implied "one" MSB
Most significant bit
In computing, the most significant bit is the bit position in a binary number having the greatest value...
) 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
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
) 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
Integer
The integers are formed by the natural numbers together with the negatives of the non-zero natural numbers .They are known as Positive and Negative Integers respectively...
operations are less susceptible to subtle chip-to-chip variations that could corrupt the lossless nature of the compression (the Pentium floating point bug
Pentium FDIV bug
The Pentium FDIV bug was a bug in the Intel P5 Pentium floating point unit . Certain floating point division operations performed with these processors would produce incorrect results...
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. 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. A 32-bit error detection code to the generated streams is included to maintain user confidence in the integrity of WavPack's compression.
WavPack source code is portable, and has been compiled on several Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
and Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems (Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, Solaris, FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
, OpenBSD
OpenBSD
OpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
, NetBSD
NetBSD
NetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...
, Compaq Tru64, HP-UX
HP-UX
HP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...
...) as well as Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
, Palm OS
Palm OS
Palm OS is a mobile operating system initially developed by Palm, Inc., for personal digital assistants in 1996. Palm OS is designed for ease of use with a touchscreen-based graphical user interface. It is provided with a suite of basic applications for personal information management...
, and OpenVMS
OpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
. It works on many architectures, including x86, ARM
ARM architecture
ARM is a 32-bit reduced instruction set computer instruction set architecture developed by ARM Holdings. It was named the Advanced RISC Machine, and before that, the Acorn RISC Machine. The ARM architecture is the most widely used 32-bit ISA in numbers produced...
, PowerPC
PowerPC
PowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
, AMD64, IA-64, SPARC
SPARC
SPARC is a RISC instruction set architecture developed by Sun Microsystems and introduced in mid-1987....
, Alpha
DEC Alpha
Alpha, originally known as Alpha AXP, is a 64-bit reduced instruction set computer instruction set architecture developed by Digital Equipment Corporation , designed to replace the 32-bit VAX complex instruction set computer ISA and its implementations. Alpha was implemented in microprocessors...
, PA-RISC
PA-RISC
PA-RISC is an instruction set architecture developed by Hewlett-Packard. As the name implies, it is a reduced instruction set computer architecture, where the PA stands for Precision Architecture...
, MIPS
MIPS architecture
MIPS is a reduced instruction set computer instruction set architecture developed by MIPS Technologies . The early MIPS architectures were 32-bit, and later versions were 64-bit...
and Motorola 68k
68k
The Motorola 680x0/m68000/68000 is a family of 32-bit CISC microprocessors. During the 1980s and early 1990s, they were popular in personal computers and workstations and were the primary competitors of Intel's x86 microprocessors...
.
A cut-down version of WavPack was developed for the Texas Instruments TMS320 series Digital Signal Processor. This was aimed predominantly at encouraging manufacturers to incorporate WavPack compression (and de-compression) into portable memory audio recorders. This version supported features that were applicable only to embedded applications (stream compression in real-time, selectable compression rate) and dropped off features that only applied to full computer systems (self extraction, high compression modes, 32-bit floats). The TMS320 series DSPs are native integer devices, and support WavPack well. Some 'special' features of the full WavPack software were included (ability to generate a correction 'file' (stream) for example) and others were excluded. The port was based on version 4.
WavPack support was added to WinZip
WinZip
WinZip is a proprietary file archiver and compressor for Microsoft Windows and Mac OS X, developed by WinZip Computing...
starting with version 11.0 beta, released in October 2006. This extension to the ZIP file format
ZIP (file format)
Zip is a file format used for data compression and archiving. A zip file contains one or more files that have been compressed, to reduce file size, or stored as is...
was included by PKWARE
PKZIP
PKZIP is an archiving tool originally written by Phil Katz and marketed by his company PKWARE, Inc. The common "PK" prefix used in both PKZIP and PKWARE stands for "Phil Katz".-History:...
, the maintainers of the format, in the official APPNOTE.TXT description file starting with version 6.3.2, released on 28 September 2007.
See also
- Comparison of audio formats
- MPEG-4 SLSMPEG-4 SLSMPEG-4 SLS, or MPEG-4 Scalable to Lossless as per ISO/IEC 14496-3:2005/Amd 3:2006 , is an extension to the MPEG-4 Part 3 standard to allow lossless audio compression scalable to lossy MPEG-4 General Audio coding methods...
- FLAC
- TTATTA (codec)True Audio is a free software, real-time lossless audio codec, based on adaptive prognostic filters.Also, .tta is the generic extension to filenames of audio files created by True Audio codec.- Codec overview :...
- Monkey's AudioMonkey's AudioMonkey's Audio is a file format for audio data compression. Being a lossless format, Monkey's Audio does not discard data during the process of encoding, unlike lossy compression methods such as AAC, MP3, Vorbis and Musepack....
- Meridian Lossless PackingMeridian Lossless PackingMeridian Lossless Packing, also known as Packed PCM , is a proprietary lossless compression technique for compressing PCM audio data developed by Meridian Audio, Ltd. MLP is the standard lossless compression method for DVD-Audio content and typically provides about 1.5:1 compression on most music...