Wednesday, August 12, 2009

How to Broadcast Multimedia Contents? III Scalable Video Coding

H.264 Network Abstract Layer Header
[How to Broadcast Multimedia Contents? I Introduction]
[How to Broadcast Multimedia Contents? II Lessons from The Channel]
[How to Broadcast Multimedia Contents? IV Hierarchical Modulation]
[How to Broadcast Multimedia Contents? V Overloaded Transmission and IC]
[How to Broadcast Multimedia Contents? VI Open-Loop MIMO for Broadcast Multicast Services]
It is very challenging to deliver multimedia contents through wireless links. Diverse receivers may request the same video with different bandwidths, spatial resolutions, frame rates, computational capabilities. Heterogeneous networks with unknown network conditions. Wired and wireless links, time-varying bandwidths. One Example is when you originally code the video you don’t know which client or network situation will exist in the future. Probably have multiple different situations, each requiring a different compressed bit stream. It needs a different compressed video matched to each situation. Possible solutions include 1) compress and store MANY different versions of the same video, 2) real-time transcoding (e.g. decode/re-encode), and 3) scalable video coding.

The procedure of scalable coding includes decomposing video into multiple layers of prioritized importance, coding layers into base and enhancement bit streams, and progressively combining one or more bit streams to produce different levels of video quality. Examples of scalable coding with base and two enhancement layers, such as 1) Base layer, 2) Base + Enh1 layers, 3) Base + Enh1 + Enh2 layers. Three basic types of scalability (refine video quality along three different dimensions).
Temporal scalability → Temporal resolution
Spatial scalability → Spatial resolution
SNR (quality) scalability → Amplitude resolution
Multiple types of scalability can be combined to provide scalability along multiple dimensions

No comments: