H.324 for POTS -
Another family of standards covers
desktop videoconferencing over POTS. This family is called H.324,
which the ITU-T ratified in early 1996. H.324 covers low-bit-rate
videoconferencing between multimedia telephones. These
telephones include stand-alone video phones, PC-based video
phones, and TV-based video phones that resemble cable boxes with
built-in cameras that sit atop televisions. This standard improves on
H.320 in its flexibility. H.324 calls for transmission of real-time
video, audio, and data over V.34 modems to be video phone ready,
they must support a protocol called V.80. Part of H.324 is a newer
video codec standard called H.263. H.263 defines and requires a
new low-end SQCIF picture format of 128x96 pixels. QCIF is also
required in H.263, and FCIF is optional. H.263 is a major
breakthrough in video compression, and is substantially better than
H.261 at low data rates. However, at 384 kbps and above, the
difference is less apparent. Work is underway in the ITU-T t o
migrate H.263 into the H.320 family. However it is mandatory that
the H.324 terminal support H.261 as well as H.263. The H.324/M
series covers videoconferencing over mobile or wireless radio
networks. H.324 is critical in delivering desktop videoconferencing
products to the home and small office/home office (SOHO) market.
QCIF (Quarter Common Intermediate
Format)-
A 176-by-144 video format defined by the ITU’s
H.261 specification.
CIF
-
Display paints 352 pixels per line and 288 lines per picture,
normally displayed full-screen.
VGA -
Video Graphics Array, resolution is 640 x 480 pixels.
SVGA -
Super Video Graphics Array, resolution is 800 x 600
pixels.