Cryptography Reference
In-Depth Information
2.5.5 H.263
H.263 [21] was defined by ITU-T) as the next generation video coding for
picture phones over analog subscriber lines. It has overtaken H.261 as dom-
inant video-conferencing coding technique. The activities of H.263 started
around November 1993, and the standard was adopted in March 1996. The
main goal of this endeavor was to design a video coding standard suitable for
applications with bit rates below 64 kbits/s (the so-called very-low bit-rate
applications). During the development of H.263, it was identified that the
near-term goal would be to enhance H.261 using the same framework, and
the long-term goal would be to design a video coding standard that may be
fundamentally different from H.261 in order to achieve further improvement
in coding e
ciency. As the standardization activities move along, a number
of different versions of H.263 emerge, and they are named H.263+ (January
1998), and H.263++ or H.263 2000 (November 2000). H.263 is widely used as
coding engine for Internet video streaming, and is also the coding core of the
MPEG-4 standard.
The First Version of H.263
Based on H.261, MPEG-1 and MPEG-2, the first version of H.263 [21] has
introduced many improvements, which makes it having a superior quality to
H.261 at all bit rates and improved coding e
ciency by a factor of two at
very low bit rate. These improvements can be grouped into two categories,
baseline algorithm features and enhanced modes which are optional. The base-
line algorithm features include half-pixel motion compensation, 3-D variable
length coding of DCT coe
cients, median motion vector prediction, deleteable
GOB header overhead etc. The enhanced modes include increased motion vec-
tor range with picture extrapolation, overlapped block motion compensation
with picture extrapolation, bi-directional prediction and arithmetic entropy
coding.
H.263+
The H.263+ [22] standard incorporates numerous enhancements and new fea-
tures over the original H.263 design and is even better suited to low bit
rate and Internet applications. Compared to H.263, H.263+ has the follow-
ing improvements such as advanced Intra coding using spatial prediction,
de-blocking filter, reference picture selection, customized and flexible video
formats, scalability for resilience and multi-point and supplemental enhance-
ment information, etc.
H.263++
H.263++ [23] project added a few more enhancements to H.263+ in late
2000. Those include error resilient data partitioning, 44 block size motion
