Softage H.263 Video Codec Overview

Video codec supports baseline profile of the ITU-T Recommendation H.263, “Video coding for low bit rate communication”. Baseline profile refers to the syntax of the recommendation with no optional modes of operation. Codec design was made from scratch therefore doesn’t inherits reference ITU implementation.

Video codec features

  • Encoder part of the codec operates at constant output bit rate in order to optimize performance for such applications as videoconference. Codec dynamically adjusts quality and compression ratio at various parts of video stream to provide equal number of bits for each compressed frame;
  • High performance. All time critical algorithms are optimized for Intel IA32 architecture by means of MMX technology. Compression of a single 176×144 frame on PC (Celeron, 500 MHz) takes about 25 ms;
  • Compression control in encoding phase is made on the frame by frame basis in contrast with reference software, where macroblocks stream controls compression. Such design allows more precise and smooth selection of encoding parameters;
  • Special care is taken for algorithmic optimization. It means that most time consuming compression operations were optimized by means of design and selection of special, fast algorithms. For example:
    • Motion compensation between neighbor frames is implemented with fast compensation search algorithm;
    • High speed quantizing algorithm used. Quantizing algorithm is 6 times faster than the C-based analog.