H.263 Video Coding
H.263 is a standard videoconferencing codec. It was published
in February 1995 and has been designed for low-bitrate communication.
It is used primarily for applications with datarates less
than 64Kbits/s, but later this limitation was removed. H.263
was designed as an improvement over H.261, the previous codec
for video compression published by ITU-T, and the MPEG-1 and
The coding algorithm of H.263 is the coding algorithm of H.261 with some
improvements about performance and error recovery. For example H.263 uses
half pixel precision for motion compensation, whereas H.261 used full
pixel precision and a loop filter. As a result lots of parts of the hierarchical
structure are now optional, so the standard can be configured for lower
datarate or better error recovery.
H.263 supports five resolutions, contrary to H.261 which supports only
two: QCIF and CIF. In addition to QCIF and CIF, there is SQCIF, 4CIF,
and 16CIF. SQCIF, 4CIF and 16CIF are half, 4 and 16 times the resolution
of CIF respectively.
The drawback is that H.263 is CPU intensive, so it can’t be used
with datarates higher than 50Kbps nor play on lower-end machines.
Finally it should be noted that H.263 has a strong temporal compression
component and works better on movies where changes between
frames aren’t big.In our days, H.263 has replaced H.261
in the field of videoconferencing in most applications and
also it is used for Internet video streaming. The most important
features of H.263 are presented in the following table.
|Ideal source material||Low motion video|
|Supported bit depths||16-bit color|
|Compression time||Symmetrical, realtime|
|Encoder requirements||Any MacOS or Windows |
|Decoder requirements||PowerMac or Pentium |
|Encoder availability||Built into QuickTime 3|
|Decoder availability||Built into QuickTime 3|
|Algorithm||Discrete Cosine Transform (DCT) |
with Motion Compensation
based on H.261
|Manufacturer||Many, including Apple, Microsoft, Vivo|
For more information visit: H.263 - Wikipedia,
the free encyclopedia and H.263 Video Coding