The Internet Encyclopedia (Volume 3)

P1: C-46

Tuttle WL040/Bidgolio-Vol I WL040-Sample.cls June 20, 2003 17:30 Char Count= 0

RECEIVING,DECODING,ANDPLAYING THEVIDEO 561

server has some specialized software that allows it to

manage a data stream as it is being transmitted through

the network. It utilizes the streaming protocols (RTP and

RTSP) to transmit the video file.

A Web server can be used to stream video, but it has

been designed to transfer text and images over the Internet

and it does not have the means to control a stream (Strom,

2001). When a Web server is used, a user selects a video file

and it starts to be copied down to the PC using HTTP like

any other data source on the Internet. The player takes

control and the video is buffered and played. But because

the Web servers are not able to control the stream, the

delivery of the video can be erratic and the user could

experience rebuffering interruptions. Thus, it is best to use

a video server to ensure that the user will have a smooth

playback without interruptions.

Video servers have capacity limitations, and they can

only deliver a certain number of streams at any one time.

The capacity of a server is measured in the number of si-

multaneous streams that it can put out at any given point

in time. This can range from 20 to 5,000 or more, depend-

ing on the type of server (DoIt & WISC, 2002). If a user

tries to access a video file after the server has reached its

maximum capacity, the user will get a message stating that

the server is busy and to try playing the video again after

1 or 2 minutes.

It is essential to note that streaming servers require the

appropriate hardware, network connections, and techni-

cal expertise to set them up and administer them. This can

consume time and resources, so many people and busi-

nesses choose to outsource this task to a host. A host is

an agent or department that has the facilities and techni-

cal expertise to serve other people’s streaming videos and

other media content (DoIt & WISC, 2002). Hosts usually

charge a fee for their services. There are numerous hosts

that advertise on the Internet. When selecting a host, it is

important to ensure that they can support the streaming

technology being used by the client.

When using a host, the client will be able to transfer

media files from his or her local computer to a stream-

ing server. This is usually done by using special software

called an FTP client (DoIt & WISC, 2002i). The host will

set the person up with a password-protected account and

a designated amount of server space. With this situation,

the person may have text and graphics for a Web site re-

siding on a Web server. Then, he or she has streaming

files on a streaming server. This can be managed by using

certain HTML tags on the Web page that will trigger and

control the playback of the media files from the streaming

server. This involves specifying the path of the particular

video file on the streaming server. Each of the three ma-

jor streaming technologies has its own unique embedded

HTML tags for controlling the video files on servers. Many

of the encoding applications can generate these HTML

tags (DoIt & WISC, 2002).

As covered earlier in the discussion on bandwidth, not

all networks are suited for the streaming of video. Video

works best when the bandwidth of the network is contin-

uously high. However, when the bandwidth of the video

exceeds that of the network, delays in the transmission

of the data packets can occur. These delays will cause

the picture to flicker and the audio (if present) to start

Server Router Network Router

Client PC’s

Figure 2: Video on demand.

and stop. In order to deal with the issues of streaming

video and media, a new measure of network capability

have been developed. It is called quality of service (QoS)

(Compaq, 1998). Networks that have a good QoS measure

provide a guaranteed bandwidth with few delays. The net-

works that have the best QoS are those that have dedicated

connections for streaming.

Another network characteristic that needs to be consid-

ered for streaming video is the network’s ability to support

video-on-demand delivery and webcasting delivery. With

video on demand (also know as unicasting), a stream is

delivered onetoone to each client, and the user can request

the video at any time. This type of delivery can consume a

lot of network bandwidth, depending the number of users

requesting a video. According to Compaq (1998), Figure 2

shows a simple diagram of how video on demand works.

Each line in the exhibit represents a separate stream.

Webcasting, is used for live events where there can be

potentially many viewers. Webcasting delivers one stream

to many clients simultaneously. It does not consume as

much bandwidth as video on demand. But as noted pre-

viously, video on demand is much more common because

of the convenience it offers to users. Webcasting is sched-

uled for specific times and requires a lot of effort and re-

sources to coordinate. Networks that support webcasting

must have routers that are multicast capable. Figure 3

shows how a webcast works, according to Compaq (1998).

The lines in the exhibit represent the video stream (note

the single line going across the network).

RECEIVING, DECODING, AND

PLAYING THE VIDEO

Finally, at the client desktop, the user accesses the video

file. As discussed above, the user clicks on the video file

that he or she wants to view, the request is routed to

the appropriate file on the video server, and the player

technology on the user’s PC takes control of the data

Server Router Network Multicast

Router

Client PC’s

Figure 3: Webcasting.