Editing Advanced Video Coding (section)

=== Scalable video coding ===
The next major feature added to the standard was [[Scalable Video Coding]] (SVC). Specified in Annex G of H.264/AVC, SVC allows the construction of bitstreams that contain ''layers'' of sub-bitstreams that also conform to the standard, including one such bitstream known as the "base layer" that can be decoded by a H.264/AVC [[codec]] that does not support SVC. For temporal bitstream scalability (i.e., the presence of a sub-bitstream with a smaller temporal sampling rate than the main bitstream), complete [[Network Abstraction Layer#Access Units|access unit]]s are removed from the bitstream when deriving the sub-bitstream. In this case, high-level syntax and inter-prediction reference pictures in the bitstream are constructed accordingly. On the other hand, for spatial and quality bitstream scalability (i.e. the presence of a sub-bitstream with lower spatial resolution/quality than the main bitstream), the NAL ([[Network Abstraction Layer]]) is removed from the bitstream when deriving the sub-bitstream. In this case, inter-layer prediction (i.e., the prediction of the higher spatial resolution/quality signal from the data of the lower spatial resolution/quality signal) is typically used for efficient coding. The [[Scalable Video Coding]] extensions were completed in November 2007.