scalable video coding (SVC)

Video communication is determined by various factors. These include the type of video compression, its effectiveness and quality, the available and required bandwidth, the screen size and its resolution, and the available computer power.

All of these factors must be taken into account when transmitting video because, for example, it makes no sense to transmit High Definition Television( HDTV) in the CIF display format, Common Intermediate Format, or for a cell phone with a QCIF display, Quarter Common Intermediate Format, to use a signal in Standard Definition Television( SDTV). These examples show the necessity of Scalable Video Coding ( SVC), which adapts the transmitted video signals to the displays of the end devices and to the transmission possibilities of the network.

The heterogeneity of video communication

To cope with the heterogeneity in video communication, in the traditional approach various decoders generate video streams with different video resolutions: HD quality, SDTV, CIF, and QCIF. The situation is different with scalable video coding, where scaled bitstreams with different resolutions can be generated and retrieved from the network, depending on the end device characteristics and the network. In this constellation, a high-resolution video is compressed in a scalable video codec and then the bitstream is extracted. The end devices can retrieve the bitstream over the network in the resolution they need for their display size.

Scalable Video Coding (SVC)

Video scaling generates further data streams from the video data stream, the sub-data streams, which represent the same content as the original data stream, but with reduced frame rate or reduced image size or reduced image quality. This sid also the three scaling techniques on which Scalable Video Coding is based: temporal, spatial and quality scalability.

The scaling techniques for video

Temporal Scalability halves the frame rate from 30 Hz to 15 Hz and to 7.5 Hz. At 30 Hz, every frame is displayed; at 15 Hz, every second frame is displayed; and at 7.5 Hz, every fourth frame is displayed. Spatial scaling, or spatial scalability, is concerned with the display size of the displays. The extracted bitstream is decoded into different display sizes by means of decoders: High Definition (HD), Standard Definition( SD), which corresponds to 4CIF, into the CIF display format and QCIF for smartphones and cell phones.

In qualitative scaling, quality scalability, the sub-stream retains the original display size, but it has a lower fidelity, expressed for example in a lower signal-to- noise ratio( SNR). If network conditions cannot transmit one of the scaled video encodings, then the different scalings can be combined so that, for example, a reduced image representation (spatial) is transmitted with a lower frame rate (temporal).

With Spatial Scalability, the video image is reduced in size overall. There is also Extended Spatial Scalability( ESS), which also reduces image sections or changes the aspect ratio.