Scalable Video Coding (SVC) is the name for the Annex G extension of the H.264/MPEG-4 AVC video compression standard. SVC standardizes the encoding of a high-quality video bitstream that also contains one or more subset bitstreams. A subset video bitstream is derived by dropping packets from the larger video to reduce the bandwidth required for the subset bitstream. The subset bitstream can represent a lower spatial resolution (smaller screen), lower temporal resolution (lower frame rate), or lower quality video signal. H.264/MPEG-4 AVC was developed jointly by ITU-T and ISO/IEC JTC 1. These two groups created the Joint Video Team (JVT) to develop the H.264/MPEG-4 AVC standard.
The objective of the SVC standardization has been to enable the encoding of a high-quality video bitstream that contains one or more subset bitstreams that can themselves be decoded with a complexity and reconstruction quality similar to that achieved using the existing H.264/MPEG-4 AVC design with the same quantity of data as in the subset bitstream. The subset bitstream is derived by dropping packets from the larger bitstream.
A subset bitstream can represent a lower spatial resolution (smaller screen), or a lower temporal resolution (lower frame rate), or a lower quality video signal (each separately or in combination) compared to the bitstream it is derived from. The following modalities are possible:
SVC enables forward compatibility for older hardware: the same bitstream can be consumed by basic hardware which can only decode a low-resolution subset (i.e. 720p or 1080i), while more advanced hardware will be able decode high quality video stream (1080p).
Bit-stream scalability for video is a desirable feature for many multimedia applications. The need for scalability arises from graceful degradation transmission requirements, or adaptation needs for spatial formats, bit rates or power. To fulfill these requirements, it is beneficial that video is simultaneously transmitted or stored with a variety of spatial or temporal resolutions or qualities which is the purpose of video bit-stream scalability.
Traditional digital video transmission and storage systems are based on H.222.0/MPEG-2 TS systems for broadcasting services over satellite, cable, and terrestrial transmission channels, and for DVD storage, or on H.320 for conversational video conferencing services. These channels are typically characterized by a fixed spatio-temporal format of the video signal (SDTV or HDTV or CIF for H.320 video telephone). The application behavior in such systems typically falls into one of the two categories: it works or it doesn't work.
Modern video transmission and storage systems using the Internet and mobile networks are typically based on RTP/IP for real-time services (conversational and streaming) and on computer file formats like mp4 or 3gp. Most RTP/IP access networks are typically characterized by a wide range of connection qualities and receiving devices. The varying connection quality results from adaptive resource sharing mechanisms of these networks addressing the time varying data throughput requirements of a varying number of users. The variety of devices with different capabilities ranging from cell phones with small screens and restricted processing power to high-end PCs with high-definition displays results from the continuous evolution of these endpoints.
Scalable video coding (SVC) is one solution to the problems posed by the characteristics of modern video transmission systems. The following video applications can benefit from SVC:
As a result of the Scalable Video Coding extension, the standard contains five additional scalable profiles: Scalable Baseline, Scalable High, Scalable High Intra, Scalable Constrained Baseline and Scalable Constrained High Profile. These profiles are defined as a combination of the H.264/MPEG-4 AVC profile for the base layer (2nd word in scalable profile name) and tools that achieve the scalable extension: