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)