intro.tex

   1 Dirac is an open video codec developed by the BBC. It has been
   2 developed to address the growing complexity and cost of current video
   3 compression technologies, which provide greater compression efficiency
   4 at the expense of implementing a very large number of tools. Dirac is
   5 a powerful and flexible compression system, yet uses only a small number
   6 of core tools. A key element of its flexibility is its use of the wavelet
   7 multi-resolution transform for compressing pictures and motion-compensated
   8 residuals, which allows Dirac to be used across a very wide range of resolutions
   9 without enlarging the toolset.
  10
  11 Dirac is an Open Source software project, and reference implementations
  12 of the decoder and encoder are available at \url{http://sourceforge.net/projects/dirac}.
  13 A high-performance implementation, called Schrodinger, is also available
  14 open source at \url{http://schrodinger.sourceforge.net}.
  15
  16 Dirac offers the following features:
  17 \begin{description}
  18 \item[Multi-resolution transforms] Data is encoded using the wavelet transform,
  19 and packed into the bitstream subband by subband. High compression ratios result
  20 in a gradual loss of resolution. Lower resolution output can be obtained
  21 for low complexity decoding by extracting only the lower resolution data.
  22 \item[Inter and intra frame coding] Pictures can be encoded using motion compensation
  23 for low bit rate, or without reference to other pictures for editing, archive
  24 and other professional applications.
  25 \item[Frame and field coding] Both frames and fields can be coded.
  26 \item[Dual syntax] A low delay syntax is available for applications requiring
  27 very low, fixed, latency. This can be of the order of a few lines of input
  28 or output video. The low delay syntax is suitable for light compression
  29 for the re-use of low bandwidth infrastructure, for example carrying
  30 HDTV over SD-SDI links. The low delay syntax uses
  31 intra coding and simple Variable Length
  32 Codes for entropy codes. The core syntax provides much greater compression efficiency
  33 at the expense of a whole picture delay. The core syntax can use a highly efficient
  34 form of binary adaptive arithmetic coding, as well as motion compensation,
  35 for maximum performance.
  36 \item[CBR and VBR operation] Dirac supports both constant bit rate and
  37 variable bit rate operation.When the low delay syntax is used, the bit
  38 rate will be constant for each area (Dirac slice) in a picture to
  39 ensure constant latency.
  40 \item[Variable bit depths] 8, 10, 12 and 16 bit formats are supported.
  41 \item[Multiple chroma sampling formats] 444, 422 and 420 video are all supported.
  42 \item[Lossless and RGB coding] A common toolset is used for both lossy and lossless
  43 coding. RGB coding is supported via the YCoCg integer color transform.
  44 \item[Choice of wavelet filters] A wide range of wavelet filters can be used
  45 to trade off performance against complexity. The Daubechies (9,7) filter is
  46 supported for compatibility with JPEG2000. A Fidelity filter is provided for
  47 improved resolution scalability.
  48 \item[Simple stream navigation] The encoded stream contains picture numbers and
  49 forms a doubly-linked list with each picture header indicating an offset to
  50 the previous and next picture, to support field-accurate high-speed navigation
  51 with no parsing or decoding required.
  52 \end{description}
  53 \section{Scope}
  54 \label{introscope}
  55
  56 This specification defines the Dirac video compression system through the stream syntax,
  57  entropy coding, coefficient unpacking and picture decoding processes. The decoder
  58  operations are defined by means of a mixture of pseudocode and mathematical
  59 operations.
  60
  61 This is version $\SpecVersion$ of the Dirac specification. The document includes
  62 a full description of the Dirac stream syntax and decoder operations.
  63
  64 Dirac is a long-GOP video codec that uses wavelet transforms and motion compensation
  65  together with entropy coding, that can be readily implemented in hardware or software.
  66 Dirac is a superset of the proposed SMPTE VC-2 video codec standard which
  67 comprises the intra coding parts of this specification.
  68
  69 This version is compatible with and extends Version 1 by the addition of motion
  70  compensated coding. Version 1 corresponds exactly to the proposed SMPTE VC-2
  71  video codec standard.
  72
  73 Subsequent versions of this specification may contain additional tools.
  74