The Internet Encyclopedia (Volume 3)

P1: IML/FFX P2: IML/FFX QC: IML/FFX T1: IML

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546 VIDEOCOMPRESSION

“welcome to the sunnyphone projectTM,

universal video for a wealth of

devices

SM

.”

Dr. Immanuel Freedman explains the

development of a low bandwidth video

communications system.

Audio

Sprite

Arbitrary-

shaped

Video

Text

Graphics

Web cam

Internet

Transcoding Proxy

Server

Wireless Network

Color Palmtop

Downloaded video client

Figure 3: Audiovisual scene containing scrolling text, audio, background sprite, arbitrarily shaped video, and graphics.

from H.263. ITU-T H.261 operates on a common inter-

mediate format (CIF) source specified by section 3.1. CIF

has an aspect ratio of 4:3 with 352×288 pixels and 2:1

horizontal and vertical decimation of the color difference

signals. Quarter CIF (QCIF) further decimates the spatial

Table 3MPEG-4 Standard Profiles

Profile Objects Use

Simple Visual Rectangular video objects Mobile networks

Simple Scalable Visual Temporal and spatial scalable objects Internet

Core Visual Arbitrarily shaped and temporally scalable Internet multimedia

N-bit Visual Core visual, but 4 –12 bits pixel depth Surveillance

Scalable Texture Visual Spatial scalable coding of still (texture) objects Games, still cameras

Core Scalable Temporal and spatially scalable arbitrarily shaped objects Internet, mobile, broadcast

Advanced Scalable Texture Arbitrarily shaped texture and still images Image browsing

Advanced Core Arbitrarily shaped video objects and still image objects Interactive multimedia

streaming over Internet

Fine Granularity Scalability Truncation of bit stream at any bit position to adapt delivery Any

quality as required

extent of the CIF picture. ITU-T H.261 supports a capabil-

ity to reduce the transmitted frame rate by skipping zero

to three frames according to some external decision.

To reduce encoding delays, ITU-T H.261 supports

intracoding macroblocks rather than pictures, requires