| 词条 | Dirac (video compression format) |
| 释义 |
| name = Dirac | icon = | logo = | extension = drc | mime = | type code = | uniform type = | magic = | owner = BBC Research & Development | released = | latest release version = 2.2.3[1] | latest release date = {{Start date and age|2008|09|23|df=yes}} | genre = Video compression format | container for = | contained by = MPEG-TS, Ogg, AVI, MKV, MOV, MPEG-4 Part 12, etc. | extended from = | extended to = VC-2 | standard = SMPTE 2042-1-2009, SMPTE 2042-2-2009 (a sub-set of Dirac) | free = | url = }} Dirac is an open and royalty-free video compression format,[2] specification and system developed by BBC Research & Development.[3][4][5][6] Schrödinger and dirac-research (formerly just called "Dirac") are open and royalty-free software implementations (video codecs) of Dirac. Dirac format aims to provide high-quality video compression for Ultra HDTV and beyond,[4] 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.[1] In September of that year, version 1.0.0 of an I-frame only subset known as Dirac Pro was released[7] and has since been standardised by the SMPTE as VC-2.[5][8] Version 2.2.3 of the full Dirac specification, including motion compensation and inter-frame coding, was issued a few days later.[9] Dirac Pro was used internally by the BBC to transmit HDTV pictures at the Beijing Olympics in 2008.[10][11][12] The format implementations are named in honour of the theoretical physicists Paul Dirac and Erwin Schrödinger, who shared the 1933 Nobel Prize in physics. TechnologyDirac supports resolutions of HDTV (1920×1080) 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 2 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",[13] which makes it comparable to 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.[14] Dirac employs wavelet compression, like the JPEG 2000 and PGF image formats and the Cineform professional video codec, instead of the discrete cosine transforms used in MPEG compression formats. Two of the specific wavelets Dirac can use are nearly identical to JPEG 2000's (known as the 5/3 and 9/7 wavelets), as well as two more derived from them.[15] Dirac can be used in AVI, Ogg and Matroska container formats and is also registered for use in the MPEG-4 file format[16] and MPEG-2 transport streams.[17] VC-2Dirac Pro was proposed to the SMPTE for standardisation.[5][18][19] 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.[1][20] In 2010, the SMPTE standardised Dirac Pro as VC-2.[8][21]
The basic spec was updated in 2012, adding a new profile for lossless and near-lossless archiving.[23] Software implementations{{Update|date=May 2010}}{{Infobox software| name = Schrödinger | developer = David Schleef | latest_release_version = 1.0.11 | latest_release_date = {{Release date and age|df=yes|2012|01|23}} | genre = Video codec | license = MPL 1.1, GNU GPL 2, GNU LGPL 2, MIT License | website = diracvideo.org (Offline)}} 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 License, 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.[24] 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".[25] 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. PatentsThe 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.[26] Desktop playback and encodingAs of November 2008, Dirac video playback is supported by VLC media player (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.[27] Applications which can encode to Dirac include MediaCoder, LiVES and OggConvert, as well as FFmpeg. PerformanceThe 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 x264 scoring higher than Dirac[28]—it is now somewhat out of date.[28] 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[29] and did not include HD content. References1. ^1 2 {{cite web |url = http://diracvideo.org/specifications/ |title = Dirac Specifications |accessdate = 2011-01-04 |archiveurl = https://web.archive.org/web/20150503015104/http://diracvideo.org/download/specification/dirac-spec-latest.pdf |archivedate = 2015-05-03 }} 2. ^{{cite web |url = http://diracvideo.org/about-dirac/ |title = About Dirac |accessdate = 2012-07-15 }} 3. ^{{cite web |publisher = diracvideo.org |title = FAQ – Diracvideo |url = http://diracvideo.org/wiki/index.php/FAQ#Flavours_of_Dirac |accessdate = 2009-08-30 }} 4. ^1 {{cite web |publisher = diracvideo.org |title = About Dirac |url = http://diracvideo.org/wiki/index.php/FAQ#About_Dirac |accessdate = 2009-08-30 }} 5. ^1 2 {{cite web |url = http://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP159.pdf |format = PDF |title = BBC Research White Paper, WHP 159, November 2007, Open Technology Video Compression for Production and Post Production |author = Tim Borer |year = 2007 |accessdate = 2010-08-19 }} 6. ^{{cite web |url = http://www.bbc.co.uk/rd/projects/dirac/index.shtml |title = BBC R&D – Dirac |accessdate = 2010-08-19 }} 7. ^{{cite web |url=https://lwn.net/Articles/298755/ |title=Dirac 1.0.0 released. |last=Edge |first=Jake |date=September 17, 2008 |website=LWN.net |accessdate=July 7, 2017}} 8. ^1 2 {{cite web |url = http://standards.smpte.org/content/978-1-61482-709-2/st-2042-1-2012/SEC1.abstract |title = SMPTE 2042-1:2012 |accessdate = 2015-09-09 }} 9. ^{{cite journal |publisher = BBC |title = Dirac Specification, Version 2.2.3 |date = 23 September 2008 |url = http://diracvideo.org/download/specification/dirac-spec-latest.pdf |accessdate = 2009-07-05 |deadurl = yes |archiveurl = https://web.archive.org/web/20150503015104/http://diracvideo.org/download/specification/dirac-spec-latest.pdf |archivedate = 3 May 2015 |df = dmy-all }} 10. ^{{cite web |publisher = Broadcast Magazine (East Midland Allied Press) |title = Dirac Pro to bolster BBC HD links |url = http://www.broadcastnow.co.uk/news/2008/07/dirac_pro_to_bolster_bbc_hd_links.html }} 11. ^BBC pushes Dirac to the forefront 12. ^And now, Dirac from the Olympics, a new free codec! 13. ^{{cite web |url = http://www.bbc.co.uk/rd/projects/dirac/overview.shtml |title = Dirac Overview |publisher = BBC R&D |accessdate = 2009-01-14 }} 14. ^{{cite journal |url = http://diracvideo.org/download/specification/dirac-spec-latest.pdf |title = Dirac Specification |author = BBC Research |publisher = diracvideo.org |format = PDF |date = 23 September 2008 |accessdate = 2009-10-04|archive-url=https://web.archive.org/web/20160308225842/http://diracvideo.org/download/specification/dirac-spec-latest.pdf|archive-date=8 March 2016}} 15. ^{{cite web |url = http://dirac.sourceforge.net/documentation/algorithm/algorithm/wlt_transform.xht |title = Dirac: Wavelet transform |first = Thomas |last = Davies |date = 2008-02-06 |accessdate = 2015-09-09 }} 16. ^MP4 Registration Authority – Dirac {{Webarchive|url=https://web.archive.org/web/20090419074514/http://www.mp4ra.org/codecs.html |date=19 April 2009 }} Retrieved on 2009-07-05 17. ^SMPTE Registration Authority, LLC; Registration for format_identifier drac {{webarchive|url=https://web.archive.org/web/20090421041153/http://smpte-ra.org/mpegreg/drac.html |date=21 April 2009 }} Retrieved on 2009-07-05 18. ^{{cite web |publisher = SMPTE |title = Advancements in Compression and Transcoding: 2008 and Beyond – Supporting the March to 8K with SMPTE VC2 / Dirac |url = http://www.smpte.org/events/smpte_annual_tech/schedule/06wedspm1/ |accessdate = 2009-08-30 |archive-url = https://web.archive.org/web/20110719180141/http://www.smpte.org/events/smpte_annual_tech/schedule/06wedspm1/ |archive-date = 19 July 2011 |dead-url = yes |df = dmy-all }} 19. ^{{cite web |url = http://diracvideo.org/worlds-first-high-performance-dirac-video-codec-implementation-available/ |title = Worlds first high performance Dirac video codec implementation available |date = 6 March 2008 |accessdate = 2010-08-18 }} 20. ^{{cite web |url = http://www.bbc.co.uk/rd/projects/dirac/diracpro.shtml |title = Dirac Pro - WHAT IS DIRAC PRO? |author = BBC |accessdate = 2010-08-18 }} 21. ^{{cite web |url = http://diracvideo.org/2010/03/schroedinger-1-0-9-released/ |title = Schroedinger-1.0.9 Released, Other news - SMPTE VC-2 |date = 4 March 2010 |accessdate = 2010-08-18 }} 22. ^{{cite web |url = http://store.smpte.org/product-p/rp%202042-3-2010.htm |title = SMPTE RP 2042-3:2010, VC-2 Conformance Specification |accessdate = 2010-08-18 }} 23. ^{{cite web |url = https://kws.smpte.org/kws/public/projects/project/details?project_id=21 |title = Revision of ST 2042-1 VC-2 -- New Profile |date = 2012-09-15 |accessdate = 2015-09-09 }} 24. ^Diracvideo.org Download section – schroedinger-1.0.0.tar.gz, 22-Feb-2008 13:52, 739K, Retrieved on 2009-08-07 25. ^{{cite web |url = http://diracvideo.org/2010/03/schroedinger-1-0-9-released/ |title = Schrödinger-1.0.9 Released |accessdate = 2010-03-11 }} 26. ^{{cite web |url = http://www.diracvideo.org/wiki/FAQ#Do_you_infringe_any_patents.3F |title = Do you infringe any patents? in official FAQ |accessdate = 2009-01-14 |archiveurl = https://web.archive.org/web/20080804070759/http://diracvideo.org/wiki/FAQ#Do_you_infringe_any_patents.3F |archivedate = 4 August 2008 }} 27. ^{{cite web |url = http://diracvideo.org/wiki/index.php/Dirac_Compatibility_Matrix |title = Dirac Compatibility Matrix in official wiki |accessdate = 2009-01-14 }} 28. ^1 {{cite web |url=http://etill.net/projects/dirac_theora_evaluation/ |title=A performance assessment of the royalty-free and open video compression specifications Dirac, Dirac Pro, and Theora and their open-source implementations |date=March 2009 |format=PDF |archive-url=https://archive.is/20120707194336/http://etill.net/projects/dirac_theora_evaluation/ |archivedate=7 July 2012 |deadurl=yes |df=dmy-all }} 29. ^{{cite web |url=http://www-ee.uta.edu/Dip/Courses/EE5359/ArunaRavi_MSThesis.pdf |title=Performance analysis and comparison of Dirac video codec with H.264 / MPEG-4 Part 10 AVC (see conclusion §5) |accessdate=July 7, 2017}} External links
6 : BBC Research & Development|Free video codecs|Lossless compression algorithms|SMPTE standards|Wavelets|Open formats |
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