11. Real-time Audio and Video
11.5 Applications
In this section we introduce two popular real-time audio and video
applications: telephony and videoconferencing.
Telephony
enables people in different places in the world to
talk to each other through computer networks. The primary advantage
is that in using the Internet, people do not incur any long-distance
telephone charges. However, you may suffer audio transfer delay
caused by heavy traffic in computer networks. This delay is
typically a half second.
There are many different telephony software products available
on the market today, but most of them adapt the same working schemes.
When one party starts talking, his or her
speech signal is received by a microphone. The electric signal
is then digitized through an ADC board on the talker's computer
and stored in computer memory in a binary form.
The data then are compressed and transmitted
through the computer network. Upon arrival at the listening party,
the data are decompressed and
converted to an analog electric signal by a DAC board.
The speaker converts this electric signal to sound.
Today, most telephony products support full-duplexed conversations
(i.e., both parties talking and listening at the same time) and
half-duplexed conversations (i.e., only one party speak at a time).
However, many currently used sound cards are only support half-duplexed.
For more information, visit the
Internet Telephone Page
and
Internet Telephone FAQ .
Telephony Products
In the following, we will study a telephony product -
WebPhone to get a better
understanding of telephony.
This is the introduction page of WebPhone.
|

WebPhone 2.0 is the hottest, professional Internet
telephony product
with integrated voice-mail on the market today. With it's sleek,
user-friendly
graphical interface, WebPhone allows you to speak to the world
through the
Internet or other TCP/IP based networks without incurring any
long distance
charges. WebPhone's full duplex, encrypted, point-to-point communication
allows for unbelievable telephone-quality real-time audio that's hard to
beat.
Using WebPhone, you can talk to anyone, anywhere without
incurring
long distance charges.
|
System requirements to run WebPhone 2.0
- 80486DX-33 MHz PC or faster (75 MHz Pentium for
TrueSpeechTM).
- 4 MB of RAM
- Sound card with microphone and speaker (MCI compliant)
- Winsock 1.1 compliant stack
- 14.4 Kbps modem with data compression and error correction capabilities
- VGA card capable of displaying 256 or more colors
- Full duplex audio card required for full duplex
- Windows 3.1, WFW 3.11, WIN 95, WINNT, or WIN-OS/2Warp
- 5 MB of free disk space
WebPhone 2.0 provides the following features:
- Point-to-Point Calling via e-mail address
- Telephone quality real-time speech
- 4-Lines with Call Holding, Muting & Do Not Disturb
- Call Conferencing
- Call Transferring
- Full Duplex Voice Communications
- Personal WebPhone Directory
- User configurable Sound Effects
- Operates on the Internet as well as over any TCP/IP based LAN or WAN
For more information of WebPhone, visit
WebPhone.
Voice on the Net shows many other
telephony products.
Because different software products use different digital formats (i.e.,
sampling rate, quantization level), compression schemes,
and transport protocols, the conversation quality is different.
A/V Streaming: Not Quite Ready for Prime Time evaluates eight programs
that provide real-time streaming audio and video.
Videoconferencing is a telecommunication facility that enables a
face to face meeting between groups of
people at two or more different locations through both speech and sight.
Every party involved can see, hear and speak just as they would at a
conventional round the table meeting. Videoconferencing can be used as:
- face-to-face meeting,
- distance learning, and
- collaborate on projects with remote teams.
When a video conference starts, the participants in each party may
gather in the office or meeting room that equipped with videoconferencing
hardware (This may includes a multimedia-equipped computer, a TV camera, etc.).
The video and audio information are recorded by TV cameras and
microphones. After digitalization and compression, the information is
send to other parties through computer networks.
Videoconferencing usually involves more than
two parties, thus, multicasting is used for data transmission over the
computer networks. There are two technical methods of obtaining a
multicast functionality: (1) multiple point-to-point connection and
(2) packet network multicast technology (e.g., MBone in IP).
When the multiple point-to-point connection is used, The number of
participating parties are usually restricted to six or eight. For a big
conference (involving more than eight parties), multicast may be the
only viable option.
Videoconferencing Product
There are numerous videoconferencing products available.
They vary widely in features and cost. We study an example ---
Cu-SeeMe to get a
better understanding.
Cu-SeeMe is a videoconferencing program developed by White Pine
Software and Cornell University. Following gives technology
and major features overview of Cu-SeeMe.
Cu_SeeMe Technology Overview
Enhanced CU-SeeMe uses a unique protocol to manage, receive and rebroadcast
video and audio data. The protocol was developed specifically for TCP/IP
networks and the Internet. It is capable of running over ISDN networks with
TCP/IP network support. Person-to-person, group conferencing, and large
audience broadcasting over TCP/IP networks are all possible with CU-SeeMe
technology - with little or no added cost for making connections.
CU-SeeMe achieves low bandwidth Internet connections through software only
algorithms that reduce data transmission and save you money. It does not
require expensive hardware compression/decompression (codec) boards. SLIP
and PPP modem connections are supported; however it is recommended that
you use a 28.8k modem connection or better.
CU-SeeMe is compatible with video codec and audio standards on both Windows
and Macintosh systems, providing versatility and compatibility for the future.
CU-SeeMe can be used with most video boards that support Video for Windows.
Similarly, CU-SeeMe supports Apple's QuickTime to display video for Macintosh
computers.
System Requirements to run Cu_SeeMe
General Requirements
- TCP/IP network and node address
- 10MB hard disk space
- Modem bandwidth of 28.8k or better; 14.4k or better for audio only
- SLIP/PPP compatible
- For more specific hardware compatibility questions, refer to our FAQ pages
PC Requirements
To RECEIVE:
- 486 DX/66
or higher processor recommended (video send/receive, audio send/receive)
- Windows 95, Windows 3.1, Windows NT, or Windows for Workgroups 3.11
running in enhanced mode
- 256-color (8-bit) video with 640x480 or higher resolution
- Sound card with 8-bit sound with microphone input (needed for sending)
and speaker output
- Minimum 12MB RAM (16MB or more recommended)
- An IP network connection
- Windows Sockets compliant TCP/IP stack or PPP
- Bandwidth of 28.8Kb or better (14.4Kb for audio only)
To SEND:
Equipped to receive as outlined above with the added requirements:
- Video camera with serial port digitizer, or
- Video camera with standard NTSC output (like a camcorder) and
- Video capture board not using overlay technology
- RCA cable (composite video), or
- S-video if capture board supports it
- Recommended: Separate microphone or headset for better
"phone-like"
use
General Features of Cu_SeeMe
- Multiplatform -- Windows, Windows 95, Macintosh and Power Macintosh
- Participants -- view up 8 participant windows; unlimited number for
audio and talk window
- Caller ID -- message alert box for incoming connections
- Whiteboard for collaboration during conferences; supports multiple users
- Mosaic browser support for direct launch of CU-SeeMe from Web page
- Selectable audio compression algorithms with 100ms and 50ms sampling
settings:
-- 2.4k and 8.5k audio codecs to support 14.4k and 28.8k modem connections;
-- 16k and 32k codecs for higher bandwidth connections
- Color Support -- 24-bit true color and 4-bit greyscale
- Phone Book -- save, add, edit participant addresses and Reflector sites
- Video Compression -- standard
and high resolution settings
- Security -- password, caller ID and other conference and inbound call
security
- Installation -- easy, user friendly installation with TCP/IP network
software
Visit Cu-SeeMe for more information.
For more information on videoconferencing , visit
Videoconferencing FAQ.
For more videoconferencing products information, visit
desktop videoconferencing
products survey.
Voice on the Net and
desktop videoconferencing
products survey list many other videoconferencing products.
<shaohong@csgrad.cs.vt.edu>
Last modified: Sun Dec 8 1996