Dirac - New Video Compression Technology

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 encode standard digital PAL TV definition (720 x 576i pixels per frame at 25 frames per second) in real time; the reference implementation can encode 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.

An intra-frame-only subset of the Dirac specification, known as Dirac Pro, is being considered for standardisation as SMPTE VC-2^[2].

The codec is named in honour of the British scientist Paul Dirac.

[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.