Dirac (codec)
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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 was finalised on January 21, 2008, and further developments will only be bug fixes and constraints[1]. 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.
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[edit] 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). 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 employs wavelet compression, instead of the discrete cosine transforms used in most older codecs (such as H.264/MPEG-4 AVC or SMPTE's VC-1). Dirac is one of several projects attempting to apply wavelets to video compression. Others include Rududu [2], Snow and Tarkin. Wavelet compression has already proven its viability in the JPEG 2000 compression standard for photographic images.
[edit] The Schrödinger Project
A second implementation of the dirac codec called "Schrödinger" aims to provide portable libraries as well as accompanying GStreamer plugins. The project is written in C. It also hopes to allow embedding Dirac inside the Ogg container format. The project is named after Erwin Schrödinger.
On 22nd of February 2008, Schrödinger 1.0.0 was released. This release was able to decode HD720/25p in real-time on a Core Duo laptop.
[edit] 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.
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 will try to ensure that Dirac does not infringe any third party patents, enabling the public to use Dirac for any imaginable purpose. [3]
[edit] See also
- Internet television
- LiVES, a free and open-source video editor which can encode to Dirac.
[edit] 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
[edit] References
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