HEVC High-Level Syntax

Abstract

An HEVC bitstream consists of a sequence of data units called network abstraction layer (NAL) units. Some NAL units contain parameter sets that carry high-level information regarding the entire coded video sequence or a subset of the pictures within it. Other NAL units carry coded samples in the form of slices that belong to one of the various picture types that are defined in HEVC. Some picture types indicate that the picture can be discarded without affecting the decodability of other pictures, and other picture types indicate positions in the bitstream where random access is possible. The slices contain information on how decoded pictures are managed, both what previous pictures to keep and in which order they are to be output. Some NAL units contain optional supplementary enhancement information (SEI) that aids the decoding process or may assist in other ways, such as providing hints about how best to display the video. The syntax elements that describe the structure of the bitstream or provide information that applies to multiple pictures or to multiple coded block regions within a picture, such as the parameter sets, reference picture management syntax, and SEI messages, are known as the "high-level syntax" part of HEVC. A considerable amount of attention has been devoted to the design of the high-level syntax in HEVC, in order to make it broadly applicable, flexible, robust to data losses, and generally highly capable of providing useful information to decoders and receiving systems. R