Dirac (codec)
Encyclopedia
Dirac is an open and royalty-free video compression format
, specification and system developed by BBC Research at the BBC
. Schrödinger and dirac-research (formerly just called 'Dirac') are open and royalty-free software implementations (video codec
s) of Dirac. Dirac format aims to provide high-quality video compression for Ultra HDTV and beyond, and as such competes with existing formats such as H.264 and VC-1
.
The specification was finalised in January 2008, and further developments are only bug fixes and constraints. In September of that year, version 1.0.0 of an I-frame only subset known as Dirac Pro was released and has since been standardised by the SMPTE
as VC-2. Version 2.2.3 of the full Dirac specification, including motion compensation
and inter-frame coding, was issued a few days later. Dirac Pro was used internally by the BBC to transmit HDTV pictures at the Beijing Olympics
in 2008.
The format implementations are named in honour of the theoretical physicists Paul Dirac
and Erwin Schrödinger
, who shared the 1933 Nobel Prize in physics
.
and its competitors, e.g. Theora
, and WMV
. Dirac's implementers make the preliminary claim of "a two-fold reduction in bit rate over MPEG-2 for high definition video", which makes it comparable to the latest generation standards such as H.264/MPEG-4 AVC
and VC-1
.
Dirac supports both constant bit rate and variable bit rate operation. When the low delay syntax is used, the bit rate will be constant for each area (Dirac slice) in a picture to ensure constant latency. Dirac supports lossy and lossless compression modes.
Dirac employs wavelet compression, instead of the discrete cosine transform
s used in most older compression formats. Dirac is one of several projects attempting to apply wavelets to video compression. Others include Rududu, Snow, cineform
, REDCODE
and the now discontinued Tarkin. Wavelet compression is also used in the JPEG 2000
and PGF
compression standards for photographic images.
Dirac can be used in AVI
, Ogg
and Matroska
container formats and is also registered for the use in the MPEG-4 file format
and MPEG-2 transport streams.
, GNU GPL 2 and GNU LGPL free software licenses. Version 1.0.0 of this implementation was released on 17 September 2008.
A second implementation called Schrödinger was funded by the BBC and aims to provide high-performance, portable version of the codec whilst remaining 100% bitstream compatible. Schrödinger is written in ANSI C
and released under the same licenses as dirac-research, as well as the highly-permissive MIT License
. The Schrödinger project also provides GStreamer
plugins to enable the library to be used with that framework. On 22 February 2008, Schrödinger 1.0.0 was released. This release was able to decode HD720/25p in real-time on a Core Duo laptop.
As of the release of Schrödinger-1.0.9, "Schrödinger outperforms dirac-research in most encoding situations, both in terms of encoding speed and visual quality". With that release, most of the encoding tools in dirac-research have been ported over to Schrödinger, giving Schrödinger the same as or better compression efficiency than dirac-research.
An encoder quality testing system has been put in place at BBC to check how well new encoding tools work and to make sure bugs that affect quality are quickly fixed.
As of Schrödinger-1.0.9, the developers identified several new features that are easy to add that will improve encoder quality. They are planning more frequent releases, perhaps one a month, introducing a new encoder feature each time.
(version 0.9.2 or newer), and by applications using the GStreamer
framework (such as Songbird
, Rhythmbox
and Totem
). Support has also been added to FFmpeg
.
Applications which can encode to Dirac include MediaCoder
, LiVES
and OggConvert
, as well as FFmpeg
.
A DirectShow filter exists for both Dirac and Schrödinger, although this is not supported on versions of Windows prior to Windows
2000 and has seemingly not been updated since early 2009.
scoring higher than Dirac - it is now somewhat out of date, and is in any case of questionable scientific merit. A study on the performances of the Dirac codec, dated from August 2009, finds that the quality obtained on SDTV is inferior to the H.264 output. The study mentions HD in its conclusion, but the numbers on HD are conspicuously missing.
Video compression format
A video compression format or a video compression specification is a specification for digitally representing a video as a file or a bitstream. Examples of video compression formats are MPEG-2 Part 2, MPEG-4 Part 2, H.264 , Theora, Dirac, RealVideo RV40, and VP8...
, specification and system developed by BBC Research at the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
. Schrödinger and dirac-research (formerly just called 'Dirac') are open and royalty-free software implementations (video codec
Video codec
A video codec is a device or software that enables video compression and/or decompression for digital video. The compression usually employs lossy data compression. Historically, video was stored as an analog signal on magnetic tape...
s) of Dirac. Dirac format aims to provide high-quality video compression for Ultra HDTV and beyond, and as such competes with existing formats such as H.264 and VC-1
VC-1
VC-1 is the informal name of the SMPTE 421M video codec standard, which was initially developed as a proprietary video format by Microsoft before it was released as a formal SMPTE standard video format on April 3, 2006...
.
The specification was finalised in January 2008, and further developments are only bug fixes and constraints. In September of that year, version 1.0.0 of an I-frame only subset known as Dirac Pro was released and has since been standardised by the SMPTE
Society of Motion Picture and Television Engineers
The Society of Motion Picture and Television Engineers The Society of Motion Picture and Television Engineers The Society of Motion Picture and Television Engineers (SMPTE , founded in 1916 as the Society of Motion Picture Engineers or SMPE, is an international professional association, based in...
as VC-2. Version 2.2.3 of the full Dirac specification, including motion compensation
Motion compensation
Motion compensation is an algorithmic technique employed in the encoding of video data for video compression, for example in the generation of MPEG-2 files. Motion compensation describes a picture in terms of the transformation of a reference picture to the current picture. The reference picture...
and inter-frame coding, was issued a few days later. Dirac Pro was used internally by the BBC to transmit HDTV pictures at the Beijing Olympics
2008 Summer Olympics
The 2008 Summer Olympics, officially known as the Games of the XXIX Olympiad, was a major international multi-sport event that took place in Beijing, China, from August 8 to August 24, 2008. A total of 11,028 athletes from 204 National Olympic Committees competed in 28 sports and 302 events...
in 2008.
The format implementations are named in honour of the theoretical physicists Paul Dirac
Paul Dirac
Paul Adrien Maurice Dirac, OM, FRS was an English theoretical physicist who made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics...
and Erwin Schrödinger
Erwin Schrödinger
Erwin Rudolf Josef Alexander Schrödinger was an Austrian physicist and theoretical biologist who was one of the fathers of quantum mechanics, and is famed for a number of important contributions to physics, especially the Schrödinger equation, for which he received the Nobel Prize in Physics in 1933...
, who shared the 1933 Nobel Prize in physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...
.
Technology
Dirac supports resolutions of HDTV (1920x1080) and greater and is claimed to provide significant savings in data rate and improvements in quality over video compression formats such as MPEG-2 Part 2, MPEG-4 Part 2MPEG-4 Part 2
MPEG-4 Part 2, MPEG-4 Visual is a video compression technology developed by MPEG. It belongs to the MPEG-4 ISO/IEC standards. It is a discrete cosine transform compression standard, similar to previous standards such as MPEG-1 and MPEG-2...
and its competitors, e.g. Theora
Theora
Theora is a free lossy video compression format. It is developed by the Xiph.Org Foundation and distributed without licensing fees alongside their other free and open media projects, including the Vorbis audio format and the Ogg container....
, and WMV
Windows Media Video
'Windows Media Video is a video compression format for several proprietary codecs developed by Microsoft. The original video format, known as WMV, was originally designed for Internet streaming applications, as a competitor to RealVideo. The other formats, such as WMV Screen and WMV Image, cater...
. Dirac's implementers make the preliminary claim of "a two-fold reduction in bit rate over MPEG-2 for high definition video", which makes it comparable to the latest generation standards such as H.264/MPEG-4 AVC
H.264/MPEG-4 AVC
H.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video...
and VC-1
VC-1
VC-1 is the informal name of the SMPTE 421M video codec standard, which was initially developed as a proprietary video format by Microsoft before it was released as a formal SMPTE standard video format on April 3, 2006...
.
Dirac supports both constant bit rate and variable bit rate operation. When the low delay syntax is used, the bit rate will be constant for each area (Dirac slice) in a picture to ensure constant latency. Dirac supports lossy and lossless compression modes.
Dirac employs wavelet compression, instead of the discrete cosine transform
Discrete cosine transform
A discrete cosine transform expresses a sequence of finitely many data points in terms of a sum of cosine functions oscillating at different frequencies. DCTs are important to numerous applications in science and engineering, from lossy compression of audio and images A discrete cosine transform...
s used in most older compression formats. Dirac is one of several projects attempting to apply wavelets to video compression. Others include Rududu, Snow, cineform
CineForm
-CineForm Intermediate:CineForm Intermediate is proprietary video codec developed for CineForm Inc by David Newman and Brian Schunck. On March 30, 2011, the company was acquired by GoPro which in particular wanted to use the 3D film capabilities of the CineForm 444 Codec for its new 3D HERO®...
, REDCODE
REDCODE
REDCODE RAW is a proprietary multimedia audio/video file format owned by Red Digital Cinema Camera Company and featuring lossy compression for video contents and lossless for audio contents...
and the now discontinued Tarkin. Wavelet compression is also used in the JPEG 2000
JPEG 2000
JPEG 2000 is an image compression standard and coding system. It was created by the Joint Photographic Experts Group committee in 2000 with the intention of superseding their original discrete cosine transform-based JPEG standard with a newly designed, wavelet-based method...
and PGF
Progressive Graphics File
PGF is a wavelet-based bitmapped image format that employs lossless and lossy data compression. PGF was created to improve upon and replace the JPEG format...
compression standards for photographic images.
Dirac can be used in AVI
Audio Video Interleave
Audio Video Interleave , known by its acronym AVI, is a multimedia container format introduced by Microsoft in November 1992 as part of its Video for Windows technology. AVI files can contain both audio and video data in a file container that allows synchronous audio-with-video playback...
, Ogg
Ogg
Ogg is a free, open container format maintained by the Xiph.Org Foundation. The creators of the Ogg format state that it is unrestricted by software patents and is designed to provide for efficient streaming and manipulation of high quality digital multimedia.The Ogg container format can multiplex...
and Matroska
Matroska
The Matroska Multimedia Container is an open standard free container format, a file format that can hold an unlimited number of video, audio, picture or subtitle tracks in one file. It is intended to serve as a universal format for storing common multimedia content, like movies or TV shows...
container formats and is also registered for the use in the MPEG-4 file format
ISO base media file format
ISO base media file format defines a general structure for time-based multimedia files such as video and audio. It is used as the basis for other media file formats...
and MPEG-2 transport streams.
VC-2
Dirac Pro was proposed to the SMPTE for standardisation. The Dirac Pro specification defines an I-frame only subset of the main Dirac Specification, aimed for professional and studio use in high bitrate applications.In 2010 the SMPTE standardised Dirac Pro as VC-2.- SMPTE 2042-1-2009 VC-2 Video Compression
- SMPTE 2042-2-2009 VC-2 Level Definitions
- RP (Recommended Practices) 2047-1-2009 - VC-2 Mezzanine Level Compression of 1080P High Definition Video Sources
- SMPTE 2047-2-2010 Carriage of VC-2 Compressed Video over HD-SDI
- RP 2042-3-2010 - VC-2 Conformance Specification
Software implementations
Two software implementations of the specification currently exist. The first is the BBC's reference implementation, formerly just called Dirac but renamed dirac-research to avoid confusion. It is written in C++ and released under the Mozilla Public LicenseMozilla Public License
The Mozilla Public License is a free and open source software license. Version 1.0 was developed by Mitchell Baker when she worked as a lawyer at Netscape Communications Corporation and version 1.1 at the Mozilla Foundation...
, GNU GPL 2 and GNU LGPL free software licenses. Version 1.0.0 of this implementation was released on 17 September 2008.
A second implementation called Schrödinger was funded by the BBC and aims to provide high-performance, portable version of the codec whilst remaining 100% bitstream compatible. Schrödinger is written in ANSI C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
and released under the same licenses as dirac-research, as well as the highly-permissive MIT License
MIT License
The MIT License is a free software license originating at the Massachusetts Institute of Technology . It is a permissive license, meaning that it permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms...
. The Schrödinger project also provides GStreamer
GStreamer
GStreamer is a pipeline-based multimedia framework written in the C programming language with the type system based on GObject.GStreamer allows a programmer to create a variety of media-handling components, including simple audio playback, audio and video playback, recording, streaming and editing...
plugins to enable the library to be used with that framework. On 22 February 2008, Schrödinger 1.0.0 was released. This release was able to decode HD720/25p in real-time on a Core Duo laptop.
As of the release of Schrödinger-1.0.9, "Schrödinger outperforms dirac-research in most encoding situations, both in terms of encoding speed and visual quality". With that release, most of the encoding tools in dirac-research have been ported over to Schrödinger, giving Schrödinger the same as or better compression efficiency than dirac-research.
An encoder quality testing system has been put in place at BBC to check how well new encoding tools work and to make sure bugs that affect quality are quickly fixed.
As of Schrödinger-1.0.9, the developers identified several new features that are easy to add that will improve encoder quality. They are planning more frequent releases, perhaps one a month, introducing a new encoder feature each time.
Patents
The BBC does not own any patents on Dirac. They previously had some patent applications with plans to irrevocably grant a royalty-free licence for their Dirac-related patents to everyone, but they let the applications lapse. In addition, the developers have said they will try to ensure that Dirac does not infringe on any third party patents, enabling the public to use Dirac for any purpose.Desktop playback and encoding
As of November 2008, Dirac video playback is supported by VLC media playerVLC media player
VLC media player is a free and open source media player and multimedia framework written by the VideoLAN project.VLC is a portable multimedia player, encoder, and streamer supporting many audio and video codecs and file formats as well as DVDs, VCDs, and various streaming protocols. It is able to...
(version 0.9.2 or newer), and by applications using the GStreamer
GStreamer
GStreamer is a pipeline-based multimedia framework written in the C programming language with the type system based on GObject.GStreamer allows a programmer to create a variety of media-handling components, including simple audio playback, audio and video playback, recording, streaming and editing...
framework (such as Songbird
Songbird (software)
Songbird is a free and open source software audio player and web browser, with a stated mission "to incubate Songbird, the first Web player, to catalyze and champion a diverse, open Media Web."...
, Rhythmbox
Rhythmbox
Rhythmbox is an audio player that plays and helps organize digital music. Originally inspired by Apple's iTunes, it is free software, designed to work well under the GNOME Desktop using the GStreamer media framework. However, Rhythmbox functions on desktop environments other than GNOME.-Music...
and Totem
Totem (media player)
Totem is a media player for the GNOME computer desktop environment which runs on GNU/Linux, Solaris, BSD and other Unix and Unix-like systems. It is officially included in GNOME starting from version 2.10 , but de facto it was already included in most GNOME environments...
). Support has also been added to FFmpeg
FFmpeg
FFmpeg is a free software project that produces libraries and programs for handling multimedia data. The most notable parts of FFmpeg are libavcodec, an audio/video codec library used by several other projects, libavformat, an audio/video container mux and demux library, and the ffmpeg command line...
.
Applications which can encode to Dirac include MediaCoder
MediaCoder
MediaCoder is a transcoding program for Microsoft Windows. It has been developed by Stanley Huang since 2005.MediaCoder uses various open source audio and video codecs, among several proprietary codecs and tools to transcode different audio/video formats and has many extra features...
, LiVES
LiVES
LiVES is a free software video editing software and VJ tool, released under the GNU General Public License version 3 or later. There are binary versions available for most popular Linux distributions...
and OggConvert
OggConvert
OggConvert is an Open source tool, released under the GNU LGPL, for converting audio and video files of various types into the free Ogg Vorbis audio format, and the Theora, VP8 and Dirac video formats. It supports Ogg, Matroska and WebM containers for output. It is developed by a single author,...
, as well as FFmpeg
FFmpeg
FFmpeg is a free software project that produces libraries and programs for handling multimedia data. The most notable parts of FFmpeg are libavcodec, an audio/video codec library used by several other projects, libavformat, an audio/video container mux and demux library, and the ffmpeg command line...
.
A DirectShow filter exists for both Dirac and Schrödinger, although this is not supported on versions of Windows prior to Windows
2000 and has seemingly not been updated since early 2009.
Performance
The algorithms in the Dirac specification have been designed with the intention to provide a competitive performance as compared to state-of-the-art international standards. Whether they succeeded is an open question; while at least one comparison exists which used implementations from the second quarter of 2008 - it shows x264X264
x264 is a free software library for encoding video streams into the H.264/MPEG-4 AVC format. It is released under the terms of the GNU General Public License.-History:...
scoring higher than Dirac - it is now somewhat out of date, and is in any case of questionable scientific merit. A study on the performances of the Dirac codec, dated from August 2009, finds that the quality obtained on SDTV is inferior to the H.264 output. The study mentions HD in its conclusion, but the numbers on HD are conspicuously missing.