Dirac (codec)

Dirac is a prototype algorithm for the encoding and decoding of raw video. It was presented by the BBC in January 2004 as the basis of a new codec for the transmission of video over the Internet. The codec is still not finalised, and thus regarded as still being under development. The immediate aim is to be able to decode standard digital PAL TV definition (720 x 576i pixels per frame at 25 frames per second) in real time; the reference implementation can decode around 17 frames per second on a 3 GHz PC but extensive optimisation is planned. This implementation is written in C++ and was released at SourceForge on 11 March 2004. The codec is named in honour of the British scientist Paul Dirac.

Technology

Similar to common video codecs such as the ISO/IEC Moving Picture Experts Group (MPEG)'s MPEG-4 Part 2 or Microsoft's WMV 7, it can compress any size of picture from low-resolution QCIF (176x144 pixels) to HDTV (1920x1080) and beyond. However, it promises significant savings in bandwidth and improvements in quality over these codecs, by some claims even superior to those promised by the latest generation of codecs such as H.264/MPEG-4 AVC or SMPTE's VC-1 (which is based on Microsoft's WMV 9), by employing wavelet compression, instead of the discrete cosine transforms used in older codecs. Dirac's implementors make the preliminary claim of "a two-fold reduction in bit rate over MPEG-2 for high definition video"[1], an estimate which would put the design in about the same class of compression capability as the latest standardization efforts of H.264/MPEG-4 AVC and VC-1. MPEG-2 is the previous generation video codec used in the standard DVD format today. Dirac is one of several projects attempting to apply wavelets to video compression. Others include Rududu [2] and Snow. Also of note is the Xiph.org Foundation's Tarkin, developed by the creators of the Vorbis audio codec, which offered impressive performance but saw only limited adoption. Tarkin showed much promise, but was put on hold so its creators could focus their efforts on Theora, a less experimental video codec based on On2 Technologies' VP3. Wavelet compression is not merely experimental. It has already proven its viability in the JPEG 2000 compression standard for photographic images. However, it has not been shown to provide substantially superior compression capability than other techniques based on more traditional block-based coding. For example, H.264/MPEG-4 AVC is often as good or better in compression capability for still images, despite the wavelet-based design of JPEG-2000.^{[1][2][3][4][5]} The primary benefits of JPEG-2000 relative to other codecs are functionality aspects, such as scalability features, rather than compression capability.

Related projects

The Schrödinger project aims to provide portable libraries as well as accompanying GStreamer plugins, written in C, that implement the Dirac codec. It also hopes to allow embedding Dirac inside the Ogg container format. The project is named after Erwin Schrödinger.

License

The BBC is releasing the source to the reference implementation of Dirac under the free software and open source Mozilla Public License, the GNU GPL 2 and the GNU LGPL. This may accelerate its adoption and lower entry costs into the emerging industry of Internet television. While the BBC own some patents on Dirac, they have irrevocably granted a royalty-free license for their Dirac-related patents to everyone. In addition, the BBC have checked (by extensive patent search) that Dirac does not infringe any third party patents, enabling the public to use Dirac for any imaginable purpose.

See also

• Internet television
• LiVES, a free and open-source video editor which can encode to Dirac.

External links

• Dirac project page
• Dirac project project page on SourceForge
• BBC Research and Development the Department (largely) working on the codec
• Schrödinger project
• DirectShow filter binaries and howto

References

1. ^ P. Topiwala, T. Tran, W. Dai, "Performance Comparison of JPEG2000 and H.264/AVC High Profile Intra–Frame Coding on HD Video Sequences", SPIE Annual Conference, August 2006.
2. ^ M. Ouaret, F. Dufaux, and T. Ebrahimi, "On comparing JPEG2000 and Intraframe AVC", SPIE annual conference, August 2006
3. ^ D. Marpe, V. George, and T. Wiegand, "Performance comparison of intra-only H.264/AVC HP and JPEG2000 for a set of monochrome ISO/IEC test images", JVT-M014, 18-22 Oct., 2004
4. ^ D. Marpe, V. George, H. L. Cycon, and K. U. Barthel, "Performance Evaluation of Motion-JPEG2000 in Comparison with H.264 / AVC Operated in Intra Coding Mode", Proc. SPIE, Vol. 5266, pp. 129-137, Feb. 2004.
5. ^ D. Marpe, S. Gordon, and T. Wiegand, "H.264/MPEG4-AVC Fidelity Range Extensions: Tools, Profiles, Performance, and Application Areas", IEEE Int'l. Conf. on Image Proc., Genova, Italy, Sept. 2005