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 to 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.