The University of Southampton
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Next Generation Wireless Research Group

Wireless Video Communications

Scalable
 
Layered video compression encodes a video sequence into multiple layers, which enables us to progressively refine the reconstructed video quality at the receiver, when the network’s throughput allows this. Generally, the most important layer is referred to as the base layer (BL) and the less important layers are termed as enhancement layers (ELs), which rely on the BL. Furthermore, an EL may be further relied upon by less important ELs. Again, when the BL or an EL is lost or corrupted during its transmission, the dependent layers cannot be utilized by the decoder and must be dropped.
Given only the BL L0 having a bitrate of 128 kbits per second (kbps), the corresponding layered video decoder of Fig. 1 reconstructs the video with a resolution of quarter common intermediate format (QCIF) at 7.5 FPS. By contrast, a common intermediate format (CIF) based video sequence scanned at 30 FPS can be reconstructed with the aid of layers L0 , L1 and L2 , which require bitrates of 128 kbps, 256 kbps and 512 kbps, respectively. If the TV screen of Fig. 1 is utilized by the user, all four layers L0 ∼ L3 may also be streamed for achieving the highest video quality. In practice, the different video streaming scenarios of Fig. 1 require different bandwidth and hence achieve different visual quality. The users may rely on different video screens, such as those of mobile phones, tablet PCs, PC and TV screen, as seen in Fig. 1 for example.
 
 
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