Dirac

From MediaCoderWiki

Introduction

In January 2003, BBC R&D produced a prototype video coding algorithm, based on wavelet technology, which is different from that used in the main proprietary or standard video compression systems. Our algorithm seems to give a two-fold reduction in bit rate over MPEG-2 for high definition video (e.g. 1920x1080 pixels), its original target application. It has been further developed to optimise it for internet streaming resolutions and seems broadly competitive with state of the art video codecs.

We have put a lot of work into Dirac.

The main specification is now written and available on SourceForge. Quality portable software to implement Dirac is being delivered both on the Dirac and Schrödinger ares of SourceForge. In hardware, we are starting to see the first specialist products being designed.

The philosophy behind the Dirac codec is 'keep it simple'. This is an ambitious aim since video codecs, particularly those with state of the art performance, tend to be fearsomely complex. However, the BBC would like to collaborate with the Open Source community, academics and others to produce an open codec. It is therefore important for us to keep the principles and design as simple as possible and to provide copious documentation.

The algorithm has evolved, and is now available in useable code. This includes optimisation so that it can decode in real time. Standard definition formats should be decodable in real time on a normal (2006) laptop machine, with CPU capacity left to do real work. HD formats can be decoded on a top end machine. Java implementations are becoming available to allow other applications to be developed. Algorithmic enhancements are needed to improve the compression performance still further. The resulting codec needs to be integrated with other parts of a compression system, such as players, and interfaced using standard IO formats. We welcome help and support in creating an open and freely available compression system based on this technology.

Dirac Specification

The Dirac Specification is now essentially complete, and has reached version 0.10.4. The specification covers the stream syntax, stream parsing operations and decoding processes. A fairly complete specification of compatible extensions to support production ("Dirac Pro") is now included; details of levels and profiles are currently being added.

This specification supercedes both the Dirac stream syntax document and version 0.9 of the specification.

Dirac Specification Version 0.10.4