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Dirac is an open and royalty-free video compression format,〔(【引用サイトリンク】title=About Dirac )〕 specification and system developed by BBC Research at the BBC.〔(【引用サイトリンク】title=FAQ – Diracvideo )〕〔(【引用サイトリンク】 About Dirac )〕〔(【引用サイトリンク】title=BBC R&D – Dirac )〕 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,〔 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〔(【引用サイトリンク】 title=Dirac 1.0.0 released. () )〕 and has since been standardised by the SMPTE as VC-2.〔〔(【引用サイトリンク】title=SMPTE 2042-1:2012 )〕 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.〔(【引用サイトリンク】East Midland Allied Press) ">title=Dirac Pro to bolster BBC HD links )〕〔(BBC pushes Dirac to the forefront )〕〔(And now, Dirac from the Olympics, a new free codec! )〕 The format implementations are named in honour of the theoretical physicists Paul Dirac and Erwin Schrödinger, who shared the 1933 Nobel Prize in physics. ==Technology== Dirac 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''",〔(【引用サイトリンク】title=Dirac Overview )〕 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. 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 Direc 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. Dirac can be used in AVI, Ogg and Matroska container formats and is also registered for use in the MPEG-4 file format〔(MP4 Registration Authority – Dirac ) Retrieved on 2009-07-05〕 and MPEG-2 transport streams.〔(SMPTE Registration Authority, LLC; Registration for format_identifier drac ) Retrieved on 2009-07-05〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dirac (video compression format)」の詳細全文を読む スポンサード リンク
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