Recent
advances in technology have resulted in a rapid growth in mobile
communications. With this explosive growth, the need for reliable transmission
of complex content (audio, video, text, graphics, etc) over wireless links is
becoming an increasingly important application requirement.
1. Media Streaming Techniques
Multimedia
streaming (over IP) technologies:
By
using RTP/UDP in media channel and RTSP/TCP in control channel.
Figure 1 shows a typical example of architecture of the resource delivery test bed which is from MPEG document N5494.
Another example
is Content Delivery Networks.
CDNs
have been widely used to provide low latency, scalability, fault tolerance, and
load balancing for the delivery of web content and more recently streaming
media.
<Figure
1> Architecture of the Resource Delivery Test Bed (source: N5494 MPEG
document)
And
in a typical video streaming system, video sequences are encoded in high
quality in advanced and stored in the server. Because different networks may
have different bandwidths, a gateway can include a transcoder to adapt the
video bit rates in order to provide video services to users on different
networks. [see our research area page about ¡°Media Transcoding¡±]
2. Error Resilient Streaming
Wireless
channels are typically noisy and suffer from a number of channel degradations
such as bit errors and burst errors due to fading and multipath reflections.
When the compressed video data is transmitted over noisy communication
channels, errors are introduced into the bitstream. So far, many techniques
have been studied to make it more error-resilient.
2.1 Multiple Description Streaming
Multiple
description coding addresses the problem of encoding a source for transmission
over a communication system with multiple channels. The objective of MDC is to
encode a source into two bit streams such that a high-quality reconstruction is
decodable from the two bit streams together, while a lower, but still
acceptable, quality reconstruction is achievable if only one stream is
received.
2.2 Error Resilience Tools in MPEG-4
A. Video packet
resynchronization
B. Data partitioning
(DP)
C. Reversible VLCs
(RVLCs)
D. Header extension code
(HEC)