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Dirac (video compression format)

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Dirac (and Dirac Pro, a subset standardised as SMPTE VC-2) is an open and royalty-free video compression format, specification and software video codec developed by BBC Research & Development.[4][5][6] Dirac aimed to provide high-quality video compression for Ultra HDTV and competed with existing formats such as H.264.[3]

Dirac
Filename extension
drc
Developed byBBC Research & Development
Initial release6 March 2008; 16 years ago (2008-03-06)[1]
Latest release
2.2.3[2]
23 September 2008; 16 years ago (2008-09-23)
Type of formatVideo coding format
Contained by
Extended toVC-2
Standard
  • SMPTE 2042-1-2022
  • SMPTE 2042-2-2017 (Level Definitions)
Open format?Yes
Free format?Yes[3]

The specification was finalised in January 2008, and further developments were only bug fixes and constraints.[2] In September of that year, version 1.0.0 of an I-frame only subset known as Dirac Pro was released and was standardised by the SMPTE as VC-2.[7][4][8] Version 2.2.3 of the full Dirac specification, including motion compensation and inter-frame coding, was issued a few days later.[2] Dirac Pro was used internally by the BBC to transmit HDTV pictures at the Beijing Olympics in 2008.[9][10]

Two open source and royalty-free video codec software implementations, libschrodinger and dirac-research, were developed. The format implementations were named in honour of the theoretical physicists Paul Dirac and Erwin Schrödinger, who shared the 1933 Nobel Prize in physics.

Technology

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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 such as Theora and WMV. Dirac's implementers made a preliminary claim of "a two-fold reduction in bit rate over MPEG-2 for high definition video", which makes it comparable to VC-1 and simpler profiles of H.264.[11]

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.[2]

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.[12]

Dirac can be used in Ogg and Matroska container formats and is also registered for use in the ISO base media (MP4) file format and MPEG transport streams.[13][14]

Patents

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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.[5]

VC-2

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Dirac Pro, an I-frame only subset of the Dirac specification, was proposed to the SMPTE for standardisation.[4][15] Dirac Pro is designed for professional and studio use of high definition video in high bitrate applications.[6] In 2010, the SMPTE standardised Dirac Pro as VC-2.[8][16]

Although work on the original Dirac codec has largely stopped, the VC-2 codec has continued to be adapted and updated for HD and UHD post-production environments. The SMPTE standards (ST) and recommended practices (RP) are as follows:[17][18]

  • SMPTE ST 2042-1:2022 – VC-2 Video Compression
  • SMPTE ST 2042-2:2017 – VC-2 Level Definitions
  • SMPTE RP 2042-3:2022 – VC-2 Conformance Specification
  • SMPTE ST 2042-4:2018 — Mapping a VC-2 Stream into the MXF Generic Container
  • SMPTE RP 2047-1:2023 – VC-2 Mezzanine Level Compression of 1080P High Definition Video Sources
  • SMPTE ST 2047-2:2010 — Carriage of VC-2 Compressed Video over HD-SDI
  • SMPTE RP 2047-3:2023 — VC-2 Level 65 Compression of High Definition Video Sources for Use with a Standard Definition Infrastructure
  • SMPTE ST 2047-4:2011 — Carriage of Level 65 VC-2 Compressed Video Over the SDTV SDI
  • SMPTE RP 2047-5:2022 — VC-2 Level 66 Compression of Ultra-High Definition Video Sources for Use with a High Definition Infrastructure
  • IETF RFC 8450 — RTP Payload Format for VC-2 High Quality (HQ) Profile

Software implementations

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Schrödinger
Developer(s)David Schleef
Stable release
1.0.11 / 23 January 2012; 12 years ago (2012-01-23)
TypeVideo codec
License
Websitesourceforge.net/projects/dirac

Two software implementations were initially developed. The BBC's reference implementation, initially called Dirac but renamed dirac-research to avoid confusion, was 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 and defines the Dirac bitstream format.[7]

A second implementation called Schrödinger was funded by the BBC and aimed to provide a high-performance, portable version of the codec whilst remaining 100% bitstream compatible. Schrödinger was written in ANSI C and released under the same licenses as dirac-research, as well as the highly-permissive MIT License. GStreamer plugins were included to enable the library to be used with that framework. On 22 February 2008, Schrödinger 1.0.0 was released, and was able to decode HD720/25p in real-time on a Core Duo laptop.[19]

By the March 2010 release of Schrödinger version 1.0.9, it was outperforming dirac-research "in most encoding situations, both in terms of encoding speed and visual quality".[20] With that release, most of the encoding tools in dirac-research were ported over to Schrödinger, giving Schrödinger the same as or better compression efficiency than dirac-research. Development of Schrödinger ceased after the 1.0.11 release in 2012.

After the standardisation of Dirac Pro as SMPTE VC-2, development began on an open source reference VC-2 encoder. The code is provided in a git repository by the BBC and is available on GitHub.[21]

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.[22]

Desktop playback and encoding

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Dirac video playback is supported by VLC media player since version 0.9.2 (2008), and by applications using the GStreamer framework. Support has also been added to FFmpeg. Applications which can encode to Dirac include FFmpeg, MediaCoder, LiVES and OggConvert.[23]

Performance

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The algorithms in the original Dirac specification were intended to provide compression performance comparable to mainstream video compression standards of the time. A 2009 comparison of the Dirac and H.264 codecs, which used implementations from the second quarter of 2008, showed x264 scoring slightly higher than Dirac.[24] Another 2009 comparison found similar results for standard definition content, but did not compare high definition (HD) video content.[25] These studies show that Dirac compression performance is close to that of MPEG-4 Part 2 Advanced Simple Profile (ASP, popularised as DivX). While also approaching low complexity H.264 encodes, a High Profile H.264 encoded video will have better compression for the same perceived quality.

Since 2010, royalty-free, open source video codecs such as VP8, VP9, and AV1 have been developed with better compression performance and more widespread adoption, including dominant streaming services such as YouTube and Netflix.[26][27]

References

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  1. ^ "Worlds first high performance Dirac video codec implementation available". Schrödinger project (Press release). SourceForge. 6 March 2008. Archived from the original on 14 December 2021. Retrieved 14 December 2021.
  2. ^ a b c d "Dirac Specification, Version 2.2.3" (PDF). diracvideo.org. BBC Research & Development. 23 September 2008. Archived from the original (PDF) on 3 May 2015. Retrieved 5 July 2009.
  3. ^ a b Davies, T.J.; Borer, Tim; Suraparaju, A. (September 2005). "White Paper 124: Dirac video compression". BBC Research & Development. BBC. Archived from the original on 29 June 2023. Retrieved 18 December 2023.
  4. ^ a b c Borer, Tim (November 2007). "White Paper 159: Open Technology video compression for production and post production". BBC Research & Development. BBC. Archived from the original on 11 September 2017. Retrieved 18 December 2023.
  5. ^ a b "Frequently Asked Questions". diracvideo.org. BBC Research & Development. Archived from the original on 23 July 2010. Retrieved 30 August 2009.
  6. ^ a b "Project: VC-2". BBC Research & Development. BBC. January 2009. Archived from the original on 12 July 2022. Retrieved 18 December 2023.
  7. ^ a b Edge, Jake (17 September 2008). "Dirac 1.0.0 released". LWN.net. Archived from the original on 14 September 2016. Retrieved 7 July 2017.
  8. ^ a b "SMPTE Standard: 2042-1:2022, VC-2 Video Compression". Society of Motion Picture and Television Engineers. 2022. Archived from the original on 18 December 2023. Retrieved 18 December 2023.
  9. ^ "Dirac Pro to bolster BBC HD links". Broadcast Magazine. East Midland Allied Press. 16 July 2008. Archived from the original on 2 December 2021. Retrieved 18 December 2023.
  10. ^ Yoshida, Junko (15 September 2008). "And now, Dirac from the Olympics, a new free codec!". EE Times. UBM Tech. Retrieved 18 December 2023.
  11. ^ "Dirac Overview". BBC Research & Development. Archived from the original on 9 January 2013. Retrieved 14 January 2009.
  12. ^ Davies, Thomas (6 February 2008). "Dirac: Wavelet transform". Archived from the original on 8 May 2015. Retrieved 9 September 2015.
  13. ^ "Codecs". MP4 Registration Authority. International Standards Organisation. Archived from the original on 7 October 2023. Retrieved 18 December 2023.
  14. ^ "List of Registered MPEG TS Identifiers". SMPTE Registration Authority. Society of Motion Picture and Television Engineers. Archived from the original on 21 April 2009. Retrieved 18 December 2023.
  15. ^ Advancements in Compression and Transcoding 2008 and Beyond – Supporting the March to 8K with Dirac and Dirac Pro (SMPTE VC2): The Dirac Family. SMPTE Technical Conference. IEEE. 2008. Archived from the original on 18 December 2023. Retrieved 18 December 2023.
  16. ^ "Schroedinger-1.0.9 Released, Other news – SMPTE VC-2". diracvideo.org. BBC Research & Development. 4 March 2010. Archived from the original on 8 March 2010. Retrieved 18 October 2010.
  17. ^ "SMPTE 2042 family of documents (VC-2)". SMPTE Document Library. Society of Motion Picture and Television Engineers. Archived from the original on 18 December 2023. Retrieved 18 December 2023.
  18. ^ "SMPTE 2047 family of documents (VC-2)". SMPTE Document Library. Society of Motion Picture and Television Engineers. Archived from the original on 18 December 2023. Retrieved 18 December 2023.
  19. ^ "Schroedinger 1.0.0 released". LWN.net. Eklektix. 27 February 2008. Archived from the original on 13 March 2016. Retrieved 18 December 2023.
  20. ^ "Schrödinger-1.0.9 Released". diracvideo.org. BBC Research & Development. 4 March 2010. Archived from the original on 8 March 2010. Retrieved 11 March 2010.
  21. ^ "VC-2 Reference Encoder and Decoder". BBC. Archived from the original on 5 August 2023. Retrieved 18 December 2023 – via GitHub.
  22. ^ Heathcote, Jonathan (7 April 2021). "VC-2 Video coding: Getting it right". BBC Reaearch & Development. BBC. Archived from the original on 20 June 2022. Retrieved 18 December 2023.
  23. ^ "Wiki: Dirac Compatibility Matrix". diracvideo.org. BBC Research & Development. Archived from the original on 8 November 2008. Retrieved 14 January 2009.
  24. ^ Halbach, Till (March 2009). "A performance assessment of the royalty-free and open video compression specifications Dirac, Dirac Pro, and Theora and their open-source implementations". Archived from the original on 7 July 2012.
  25. ^ Ravi, Aruna; Rao, K. R. (July 2011). "Performance Analysis and Comparison of the Dirac Video Codec with H.264/MPEG-4 Part 10 AVC". International Journal of Wavelets, Multiresolution and Information Processing. 9 (4): 635–654. doi:10.1142/S0219691311004341. hdl:10106/1740. Archived from the original on 3 August 2023. Retrieved 18 December 2023.
  26. ^ Shankland, Stephen (28 December 2012). "Google's new VP9 video technology reaches public view". CNET. Retrieved 19 December 2023.
  27. ^ Peters, Jay (11 November 2021). "You can see Netflix's new AV1 streaming tech on select TVs and the PS4 Pro". The Verge. Vox Media. Retrieved 19 December 2023.
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