Introduction - Scalable Continuous Media Streaming Systems - page 6

Active Client

Passive Client

Network

Conferencing
Server

Active Client

Figure 1.2 Real-time continuous media data delivery in a video conferencing application

Client

Media Server

Playback audio/video

Network

Directory
Server

TV

Set-top box

Upload

A/V
Encoder

A/V Source

Figure 1.3 Soft-real-time continuous media data delivery in video-on-demand applications

for real-time delivery may even surpass that of data integrity and presentation timing integrity.
For example, it may be necessary to allow data loss (or even discard data) and/or playback
jitter in order to meet the given delay budget.
On the other hand, for soft-real-time delivery, there is no delay budget given. Instead, the
system must deliver the media data so that data integrity and presentation timing integrity are
preserved, while reducing the delay as far as possible. Examples of soft-real-time delivery
are video-on-demand (VoD) where a user can select and playback a video title from the video
collection available at a video server over the network as shown in Figure 1.3. These applications
are far more tolerable to longer start-up delays (e.g., in seconds) as long as smooth playback
is maintained after playback has started.