re as an integral part of this Recommendation International Standard. 3.162 variable length coding (VLC): A reversible procedure for entropy coding that assigns shorter bit strings to symbols expected to be more frequent and longer bit strings to symbols expected to be less frequent. 3.163 VCL NAL unit: A collective term for coded slice NAL units and coded slice data partition NAL units. 3.164 zig-zag scan: A specific sequential ordering of transform coefficient levels from (approximately) the lowest spatial frequency to the highest. Zig-zag scan is used for transform coefficient levels in frame macroblocks. Abbreviations For the purposes of this Recommendation | International Standard, the following abbreviations apply: CABAC Context-based Adaptive Binary Arithmetic Coding CAVLC Context-based Adaptive Variable Length Coding Constant Bit Rate Coded Picture Buffer Decoded Picture Buffer Decoder under test First-In, First-Out Hypothetical Reference Decoder Hypothetical Stream Scheduler Instantaneous Decoding Refresh Rec. ITU-T H.264 (01/2012) Least Significant Bit Macroblock MBAFF Macroblock-Adaptive Frame-Field Coding Most Significant Bit Multiview Video Coding Network Abstraction Layer Raw Byte Sequence Payload Supplemental Enhancement Information String Of Data Bits Scalable Video Coding Universal Unique Identifier Variable Bit Rate Video Coding Layer Variable Length Coding Video Usability Information Conventions NOTE - The mathematical operators used in this Specification are similar to those used in the C programming language. However, integer division and arithmetic shift operations are specifically defined. Numbering and counting conventions generally begin from 0. Arithmetic operators The following arithmetic operators are defined as follows: Addition Subtraction (as a two-argument operator) or negation (as a unary prefix operator) Multiplication, including matrix multiplication Exponentiation. Specifies X to the power of y. In other contexts, such notation is used for superscripting not intended for interp