Dirac (video compression format)

This article may contain excessive or inappropriate references to self-published sources. (July 2021)
23 September 2008; 14 years ago (2008-09-23)
Type of formatVideo coding formatContained byMPEG-TS, Ogg, AVI, MKV, MOV, MPEG-4 Part 12, etc.Extended toVC-2StandardSMPTE 2042-1-2009, SMPTE 2042-2-2009 (a sub-set of Dirac)Open format?YesFree format?Yes

Dirac is an open and royalty-free video compression format, specification and system developed by BBC Research & Development. 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 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.


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", 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 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.

Dirac can be used in AVI, Ogg and Matroska container formats and is also registered for use in the MPEG-4 file format and MPEG-2 transport streams.


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

The basic spec was updated in 2012, adding a new profile for lossless and near-lossless archiving.

Software implementations

See Compression methods for techniques and Compression software for codecs

This page was last updated at 2023-05-13 05:19 UTC. Update now. View original page.

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