Advance Professional Video

Introduction This document defines the bitstream formats and decoding process for Advanced Professional Video (APV) Codec. The APV codec is a professional video codec that was developed in response to the need for professional level high quality video recording and post production. The primary purpose of the APV codec is for use in professional video recording and editing workflows for various types of content. The APV codec supports the following features:

Perceptually lossless video quality that is close to raw video quality
Low complexity and high throughput intra frame only coding without pixel domain prediction
Support for high bit-rates up to a few Gbps for 2K, 4K and 8K resolution content, enabled by a lightweight entropy coding scheme
Frame tiling for immersive content and for enabling parallel encoding and decoding
Support for various chroma sampling formats from 4:2:2 to 4:4:4, and bit-depths from 10 to 16
Support for multiple decoding and re-encoding without severe visual quality degradation

Terms

Terms and definitions

Block: MxN (M-column by N-row) array of samples, or an MxN array of transform coefficients
byte-aligned: a position in a bitstream that is an integer multiple of 8 bits from the position of the first bit in the bitstream
chroma: a sample array or single sample representing one of the two color difference signals related to the primary colors, represented by the symbols Cb and Cr
coded frame: a coded representation of a frame containing all macroblocks of the frame
coded representation: a data element as represented in its coded form
component: array or a single sample from one of the three arrays (luma and two chroma) that compose a frame in 4:2:2, or 4:4:4 color format
decoded frame: a frame derived by decoding a coded frame
decoder: an embodiment of a decoding process
decoding process: a process specified that reads a bitstream and derives decoded frames from it
encoder: an embodiment of an encoding process
encoding process: a process that produces a bitstream conforming to this document
flag: a variable or single-bit syntax element that can take one of the two possible values: 0 and 1
frame: an array of luma samples and two corresponding arrays of chroma samples in 4:2:2, and 4:4:4 color format
Frame Data: a syntax structure containing coded representation of a frame
Frame Data stream: a sequence of Frame Data
Level: a defined set of constraints on the values that may be taken by the syntax elements and variables of this document, or the value of a transform coefficient prior to scaling
luma: a sample array or single sample representing the monochrome signal related to the primary colors, represented by the symbol or subscript Y or L
MB (macroblock): square block of luma samples and two corresponding blocks of chroma samples of a frame
Partitioning: a division of a set into subsets such that each element of the set is in exactly one of the subsets
prediction: an embodiment of the prediction process
prediction process: use of a predictor to provide an estimate of the data element currently being decoded
predictor: a combination of specified values or previously decoded data elements used in the decoding process of subsequent data elements
Profile: a specified subset of the syntax of this document
QP (quantization parameter): a variable used by the decoding process for scaling of transform coefficient levels
raster scan: a mapping of a rectangular two-dimensional pattern to a one-dimensional pattern such that the first entries in the one- dimensional pattern are from the top row of the two- dimensional pattern scanned from left to right, followed by the second, third, etc., rows of the pattern each scanned from left to right
raw bitstream: an encapsulation of a Frame Data stream where for each frame, a field indicating the size of Frame Data precedes the Frame Data
source: a term used to describe the video material or some of its attributes before encoding process
syntax element: an element of data represented in the bitstream
syntax structure: zero or more syntax elements present together in the bitstream in a specified order
tile: a rectangular region of MBs within a particular tile column and a particular tile row in a frame
tile column: a rectangular region of MBs having a height equal to the height of the frame and width specified by syntax elements in the frame header
tile row: a rectangular region of MBs having a height specified by syntax elements in the frame header and a width equal to the width of the frame
tile scan: a specific sequential ordering of MBs partitioning a frame in which the MBs are ordered consecutively in MB raster scan in a tile and the tiles in a frame are ordered consecutively in a raster scan of the tiles of the frame
transform coefficient: a scalar quantity, considered to be in a frequency domain, that is associated with a particular one- dimensional or two-dimensional index

Abbreviated terms

I: intra
LSB: least significant bit
MSB: most significant bit
RGB: Red, Green and Blue

Conventions used in this document

General The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in .

Operators The operators and the order of precedence are the same as used in the C programming language , with the exception of the operators described in the and

Arithmetic operators

// : an integer division with rounding of the result toward zero. For example, 7/4 and -7/-4 are rounded to 1 and -7/4 and 7/-4 are rounded to -1
% : a modulus. x % y is a remainder of x divided by y
min(x,y): the minimum value of the values x and y
max(x,y): the maximum value of the values x and y
ceil(x): the smallest integer value that is larger than or equal to x
clip(x,y,z): clip(x,y,z)=max(x,min(z,y))
sum (i=x, y, f(i)) : a summation of f(i) with i taking all integer values from x up to and including y

Bitwise operators

& (bit-wise "and"): When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on arguments with unequal bitdepts, the bitdepts are equliazed by adding zeros in significant positions to the argument with lower bitdepth.
| (bit-wise "or"): When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on arguments with unequal bitdepts, the bitdepts are equliazed by adding zeros in significant positions to the argument with lower bitdepth.
x >> y: arithmetic right shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the most significant bits (MSBs) as a result of the right shift have a value equal to the MSB of x prior to the shift operation.
x << y: arithmetic left shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the least significant bits (LSBs) as a result of the left shift have a value equal to 0.

Range notation

x = y..z

x takes on integer values starting from y to z, inclusive, with x, y, and z being integer numbers and z being greater than y

Order of operations precedence When order of precedence is not indicated explicitly by use of parentheses, operations are evaluated in the following order

Operations of a higher precedence are evaluated before any operation of a lower precedence. specifies the precedence of operations from highest to lowest; operations closer to the top of the table indicates a higher precedence.
Operations of the same precedence are evaluated sequentially from left to right.

Operation precedence from highest (top of the table) to lowest (bottom of the table)

operations (with operands x, y, and z)
"x++", "x--"
"!x", "-x" (as a unary prefix operator)
x^y (power)
"x * y", "x / y", "x // y", "x % y"
"x + y", "x - y", "sum (i=x, y, f(i))"
"x << y", "x >> y"
"x < y", "x <= y", "x > y", "x >= y"
"x == y", "x != y"
"x & y"
"x \| y"
"x && y"
"x \|\| y"
"x ? y : z"
"x..y"
"x = y", "x += y", "x -= y"

Variables, syntax elements and tables Each syntax element is described by its name in all lowercase letters and its type is provided next to the syntax code in each row. The decoding process behaves according to the value of the syntax element and to the values of previously decoded syntax elements. In some cases, the syntax tables may use the values of other variables derived from syntax elements values. Such variables appear in the syntax tables, or text, named by a mixture of lower case and uppercase letters and without any underscore characters. Variables with names starting with an uppercase letter are derived for the decoding of the current syntax structure and all dependent syntax structures. Variables with names starting with an uppercase letter may be used in the decoding process for later syntax structures without mentioning the originating syntax structure of the variable. Variables with names starting with a lowercase letter are only used within the section in which they are derived. Functions that specify properties of the current position in the bitstream are referred to as syntax functions. These functions are specified in and assume the existence of a bitstream pointer with an indication of the position of the next bit to be read by the decoding process from the bitstream. An one-dimensional array is referred to as a list. A two-dimensional array is referred to as a matrix. Arrays can either be syntax elements or variables. Square parentheses are used for the indexing of arrays. In reference to a visual depiction of a matrix, the first square bracket is used as a column (horizontal) index and the second square bracket is used as a row (vertial) index. A specification of values of the entries in rows and columns of an array may be denoted by {{...}{...}}, where each inner pair of brackets specifies the values of the elements within a row in increasing column order and the rows are ordered in increasing row order. Thus, setting a matrix s equal to {{1 6}{4 9}} specifies that s[0][0] is set equal to 1, s[1][0] is set equal to 6, s[0][1] is set equal to 4, and s[1][1] is set equal to 9. Binary notation is indicated by enclosing the string of bit values by single quote marks. For example, '01000001' represents an eight-bit string having only its second and its last bits (counted from the most to the least significant bit) equal to 1. Hexadecimal notation, indicated by prefixing the hexadecimal number by "0x", may be used instead of binary notation when the number of bits is an integer multiple of 4. For example, 0x41 represents an eight-bit string having only its second and its last bits (counted from the most to the least significant bit) equal to 1. A value equal to 0 represents a FALSE condition in a test statement. The value TRUE is represented by any value different from zero.

Processes Processes are used to describe the decoding of syntax elements. A process has a separate specification and invoking. When invoking a process, the assignment of variables is specified as follows:

If the variables at the invoking and the process specification do not have the same name, the variables are explicitly assigned to lower case input or output variables of the process specification.
Otherwise (the variables at the invoking and the process specification have the same name), the assignment is implied.

In the specification of a process, a specific coding block may be referred to by the variable name having a value equal to the address of the specific coding block.

Formats and processes used in this document

Bitstream formats This section specifies the bitstream of the Advanced Professional Video (APV) Codec. The bitstream can be in one of two formats, the Frame Data stream format or the raw bitstream file storage format. The Frame Data stream format is conceptually the more "basic" type. It consists of a sequence of syntax structure called Frame Data. The raw bitstream file storage format can be constructed from the Frame Data stream format by prefixing each Frame Data with a frame size field to form a stream of bytes. The raw bitstream file storage format is specified in Appendix B.

Source, decoded and output frame formats This section specifies the relationship between the source and the decoded frames that are the results of the decoding process. The video source that is represented by the bitstream is a sequence of frames. The source and decoded frames are each comprised of one or more sample arrays:

Luma and two chroma (YCbCr or YCgCo).
Green, blue, and red (GBR, also known as RGB).
Arrays representing other unspecified tri-stimulus color samplings (for example, YZX, also known as XYZ).

For the convenience of notation and terminology in this document, the variables and terms associated with these arrays can be referred to as luma (or L or Y) and chroma, where the two chroma arrays can be referred to as Cb and Cr; regardless of the actual color representation method in use. The variables SubWidthC, SubHeightC and NumComp are specified in , depending on the chroma format sampling structure, which is specified through chroma_format_idc. Other values of chroma_format_idc, SubWidthC, SubHeightC and NumComp may be specified in the future. SubWidthC, SubHeightC and NumComp values derived from chroma_format_idc

chroma_format_idc	Chroma format	SubWidthC	SubHeightC	NumpComp
0	reserved	reserved	reserved	reserved
1	reserved	reserved	reserved	reserved
2	4:2:2	2	1	3
3	4:4:4	1	1	3
4..7	reserved	reserved	reserved	reserved

In 4:2:2 sampling, each of the two chroma arrays has the same height and half the width of the luma array. In 4:4:4 sampling, each of the two chroma arrays has the same height and width as the luma array. The number of bits necessary for the representation of each of the samples in the luma and chroma arrays in a video sequence is in the range of 10 to 16, inclusive. When the value of chroma_format_idc is equal to 2, the chroma samples are co-sited with the corresponding luma samples and the nominal locations in a frame are as shown in .

Nominal vertical and horizontal locations of 4:2:2 luma and chroma samples in a frame When the value of chroma_format_idc is equal to 3, for each frame, all the array samples are co-sited and the nominal locations in a frame are as shown in .

Nominal vertical and horizontal locations of 4:4:4 luma and chroma samples in a frame The samples are processed in units of MBs. The variables MbWidth and MbHeight, which specify the width and height of the luma arrays for each MB, are defined as follows:

MbWidth = 16
MbHeight = 16

The variables MbWidthC and MbHeightC, which specify the width and height of the chroma arrays for each MB, are derived as follows:

MbWidthC = MbWidth // SubWidthC
MbHeightC = MbHeight // SubHeightC

Partitioning of a frame

Partitioning of a frame into tiles This section specifies how a frame is partitioned into tiles. A frame is divided into tiles. A tile is a group of MBs that cover a rectangular region of a frame and is processed independently of other tiles. Every tile has the same width and height, except possibly tiles at the right or bottom frame boundary when the frame width or height is not a multiple of the tile width or height, respectively. The tiles in a frame are scanned in raster order. Within a tile, the MBs are scanned in raster order. Each MB is comprised of one (MbWidth) x (MbHeight) luma array and two corresponding chroma sample arrays. For example, a frame may be divided into 6 tiles (3 tile columns and 2 tile rows) as shown in Figure 3: Frame with 10 by 8 MBs that is partitioned into 6 tiles. In this example, the tile size is defined as 4 column MBs and 4 row MBs. In case of the third and sixth tiles (in raster order), the tile size is 2 column MBs and 4 row MBs since the frame width is not multiple of the tile width.

Frame with 10 by 8 MBs that is partitioned into 6 tiles

Spatial or component-wise partitioning The following divisions of processing elements form spatial or component-wise partitioning:

the division of each frame into components;
the division of each frame into tile columns;
the division of each frame into tile rows;
the division of each tile column into tiles;
the division of each tile row into tiles;
the division of each tile into color components;
the division of each tile into MBs;
the division of each MB into blocks.

Scanning processes

Zig-zag scan Inputs to this process are:

a variable blkWidth specifying the width of a block, and
a variable blkHeight specifying the height of a block.

Output of this process is the array zigZagScan[sPos]. The array index sPos specifies the scan position ranging from 0 to (blkWidth * blkHeight)-1. Depending on the value of blkWidth and blkHeight, the array zigZagScan is derived as follows:

Pseudo-code for zig-zag scan =0&&y=0&&x

Inverse scan Inputs to this process are:

a variable blkWidth specifying the width of a block, and
a variable blkHeight specifying the height of a block.

Output of this process is the array inverseScan[rPos]. The array index rPos specifies the raster scan position ranging from 0 to (blkWidth * blkHeight)-1. Depending on the value of blkWidth and blkHeight, the array inverseScan is derived as follows:

The variable forwardScan is derived by invoking zig-zag scan order 1D array initialization process as specified in with input parameters blkWidth and blkHeight.
The output variable inverseScan is derived as follows:

Pseudo-code for inverse zig-zag scan

Syntax and semantics

Method of specifying syntax The syntax tables specify a superset of the syntax of all allowedbitstreams. Note that an actual decoder must implement some meansfor identifying entry points into the bitstream and some means toidentify and handle non-conforming bitstreams. The methods foridentifying and handling errors and other such situations are notspecified in this document. The APV bitstream is described in this document using syntax code based on the C programming language and uses its if/else, while,and for keywords as well as functions defined within this document. The syntax table in syntax code is presented in a two-column formatsuch as shown in . In this form, the type column provides a type referenced in that same line of syntax code by using syntax elements processing function defined in

A depiction of type-labeled syntax code for syntax description in this document

Syntax functions and descriptors The functions presented in this document are used in the syntacticaldescription. These functions are expressed in terms of the value ofa bitstream pointer that indicates the position of the next bit tobe read by the decoding process from the bitstream.

byte_aligned()

If the current position in the bitstream is on a byte boundary, i.e., the next bit in the bitstream is the first bit in a byte, the return value of byte_aligned() is equal to TRUE.
Otherwise, the return value of byte_aligned() is equal to FALSE.

more_data_in_tile()

If the current position in the tileIdx-th tile() syntax structure is less than TileSize[ tileIdx ] in bytes from the beginning of the tile_header() syntax structure of the tileIdx-th tile, the return value of more_data_in_tile() is equal to TURE.
Otherwise, the return value of more_data_in_tile() is equal to FALSE.

next_bits(n) This function provides the next bits in the bitstream for comparison purposes, without advancing the bitstream pointer. Provides a lookat the next n bits in the bitstream with n being its argument.

read_bits(n) This function indicate to read the next n bits from the bitstreamand advances the bitstream pointer by n bit positions. When n isequal to 0, read_bits(n) is specified to return a value equal to 0and to not advance the bitstream pointer.

Syntax element processing functions

b(8): byte having any pattern of bit string (8 bits). The parsing process for this descriptor is specified by the return value of the function read_bits(8).
f(n): fixed-pattern bit string using n bits written (from left to right) with the left bit first. The parsing process for this descriptor is specified by the return value of the function read_bits(n).
u(n): unsigned integer using n bits. The parsing process for this descriptor is specified by the return value of the function read_bits(n) interpreted as a binary representation of an unsigned integer with most significant bit written first.
h(v): variable-length entropy coded syntax element with the left bit first. The parsing process for this descriptor is specified in .

List of syntax

Frame Data

tile_size_minus1[tileIdx]

plus 1 indicates the size in bytes of tileIdx-th tile data (i.e., tile(tileIdx)) in raster order in a frame.

The variable TileSize[ tileIdx ] is set equal to tile_size_minus1[ tildIdx ] + 1

Frame header syntax

frame_header_size

indicates the size of the frame header in bytes.

profile_idc

indicates a profile to which the Frame Data stream conforms to as specified in . Bitstreams shall not contain values of profiles_idc other than those specified in Appendix A. Other values of profile_idc are reserved for future use.

level_idc

indicates a level to which the Frame Data stream conforms to as specified in Appendix A. Bitstreams shall not contain values of level_idc other than those specified in . Other values of level_idc are reserved for future use.

reserved_zero_8bits

shall be equal to 0 in bitstreams conforming to this version of document. Values of reserved_zero_8bits greater than 0 are reserved for future use. Decoders conforming to a profile specified in . MUST ignore Frame Data with values of reserved_zero_8bits greater than 0.

frame_width_minus1

plus 1 specifies the width of frame in units of luma samples. frame_width_minus1 plus 1 MUST be as multiple of 2 when chroma_format_idc has a value of 2.

frame_height_minus1

plus 1 specifies the height of frame in units of luma samples.

The variables FrameWidthInMbsY, FrameHeightInMbsY, FrameWidthInSamplesY, FrameHeightInSamplesY, FrameWidthInSamplesC, FrameHeightInSamplesC, FrameSizeInMbsY, and FrameSizeInSamplesY are derived as follows:

- FrameWidthInSamplesY = frame_width_minus1 + 1
- FrameHeightInSamplesY = frame_height_minus1 + 1
- FrameWidthInMbsY = ceil(FrameWidthInSamplesY / MbWidth)
- FrameHeightInMbsY = ceil(FrameHeightInSamplesY / MbHeight)
- FrameWidthInSamplesC = FrameWidthInSamplesY // SubWidthC
- FrameHeightInSamplesC = FrameHeightInSamplesY // SubHeightC
- FrameSizeInMbsY = FrameWidthInMbsY * FrameHeightInMbsY
- FrameSizeInSamplesY = FrameWidthInSamplesY * FrameHeightInSamplesY

chroma_format_idc

specifies the chroma sampling relative to the luma sampling as specified in The value of chroma_format_idc MUST be in the range of 2 to 3, inclusive. Other values of chroma_format_idc are reserved for future use.

bit_depth_minus8

specifies the bit depth of the samples. The variables BitDepth and QpBdOffset are derived as follows:

- - BitDepth = bit_depth_minus8 + 8

- - QpBdOffset = bit_depth_minus8 * 6

bit_depth_minus8

MUST be in the range of 2 to 8, inclusive. Other values of bit_depth_minus8 are reserved for future use.

capture_time_distance

indicates time difference between the capture time of the previous frame and the current frame if there has been any frame preceding this frame.

reserved_zero_16bits

MUST be equal to 0 in bitstreams conforming to this version of document. Values of reserved_zero_16bits greater than 0 are reserved for future use. Decoders conforming to a profile specified in MUST ignore Frame Data with values of reserved_zero_16bits greater than 0.

color_description_present_flag equal to 1

specifies that color_primaries, transfer_characteristics and matrix_coefficients are present. color_description_present_flag equal to 0 specifies that color_primaries, transfer_characteristics and matrix_coefficients are not present.

color_primaries

MUST have the semantics of ColourPrimaries as specified in . When the color_primaries syntax element is not present, the value of color_primaries is inferred to be equal to 2.

transfer_characteristics

MUST have the semantics of TransferCharacteristics as specified in . When the transfer_characteristics syntax element is not present, the value of transfer_characteristics is inferred to be equal to 2.

matrix_coefficients

MUST have the semnatics of MatrixCoefficients as specified in . When the matrix_coefficients syntax element is not present, the value of matrix_coefficients is inferred to be equal to 2.

use_q_matrix

equal to 1 specifies that the quantization matrices are present. use_q_matrix equal to 0 specifies that the quantization matrices are not present.

reserved_zero_8bits

MUST be equal to 0 in bitstreams conforming to this version of document. Values of reserved_zero_8bits greater than 0 are reserved for future use. Decoders conforming to a profile specified in MUST ignore Frame Data with values of reserved_zero_8bits greater than 0.

Quantization matrix syntax

q_matrix_minus1[cIdx][x0][y0]

plus 1 specifies a scaling value in the quantization matrices. When q_matrix_minus1[cIdx][x0][y0] is not present, it is inferred to be equal to 15. The array index cIdx specifies an indicator for the color component; when chroma_format_idc is equal to 2 or 3, 0 for Y, 1 for Cb and 2 for Cr.

The quantization matrix, QMatrix[cIdx][x0][y0], is derived as follows:

QMatrix[cIdx][x0][y0] = q_matrix_minus1[cIdx][x0][y0] + 1

Tile info syntax

tile_width_in_mbs_minus1

plus 1 specifies the width of a tile in units of MBs.

tile_height_in_mbs_minus1

plus 1 specifies the height of a tile in units of MBs.

tile_size_present_in_fh_flag

equal to 1 specifies that tile_size_in_fh_minus1[tileIdx] is present in Frame header. tile_size_present_in_fh_flag equal to 0 specifies that tile_size_in_fh_minus1[tileIdx] is not present in Frame header.

tile_size_in_fh_minus1[tileIdx]

plus 1 indicates the size in bytes of tileIdx-th tile data in raster order in a frame. The value of tile_size_in_fh_minus1[tileIdx] MUST have the same value with tile_size_minus[tileIdx]. When it is not present, the value of tile_size_in_fh_minus1[tileIdx] is inferred to be equal to tile_size_minus1[tileIdx].

Metadata syntax

metadata_size

specifies the size of metadata in current Frame Data. Syntax and semantics of metadata_payload() is not defined in this document.

Filler data syntax

ff_byte

is a byte equal to 0xFF.

Tile syntax

tile_dummy_byte

has any pattern of 8-bit string.

Tile header syntax

tile_header_size

indicates the size of the tile header in bytes.

tile_index

specifies the tile index in raster order in a frame. tile_index MUST have the same value with tileIdx.

tile_data_size_minus1[i] plus 1

indicates the size of i-th color component data in a tile in bytes. The array index i specifies an indicator for the color component; when chroma_format_idc is equal to 2 or 3, 0 for Y, 1 for Cb and 2 for Cr

tile_qp[i]

specify the quantization parameter value for i-th color component. The array index i specifies an indicator for the color component; when chroma_format_idc is equal to 2 or 3, 0 for Y, 1 for Cb and 2 for Cr. Qp[i] to be used for the MBs in the tile are derived as follows

- - Qp[i] = tile_qp[i] - QpBdOffset

- - Qp[i] MUST be in the range of -QpBdOffset to 51, inclusive.

reserved_zero_8bits

MUST be equal to 0 in bitstreams conforming to this version of document. Values of reserved_zero_8bits greater than 0 are reserved for future use. Decoders conforming to a profile specified in MUST ignore Frame Data with values of reserved_zero_8bits greater than 0.

Tile data syntax

Macroblock layer syntax

abs_dc_coeff_diff

specifies the absolute value of the difference between the current DC transform coefficient level and PrevDC.

sign_dc_coeff_diff

specifies the sign of the difference between the current DC transform coefficient level and PrevDC. sign_dc_coeff_diff equal to 0 specifies that the difference has a positive value. sign_dc_coeff_diff equal to 1 specifies that the difference has a negative value.

AC coefficient coding syntax >log2BlkWidth | TransCoeff[cIdx][x0+xC][y0+yC]=0 | scanPos++ | } | PrevRun=coeff_zero_run | if(scanPos<(1<<(log2BlkWidth+log2BlkHeight))){ | abs_ac_coeff_minus1 | h(v) sign_ac_coeff | u(1) level=(abs_ac_coeff_minus1+1) | *(1-2*sign_ac_coeff) | blkPos=ScanOrder[scanPos] | xC=blkPos&((1<>log2BlkWidth | TransCoeff[cIdx][x0+xC][y0+yC]=level | scanPos++ | PrevLevel=abs_ac_coeff_minus1+1 | if(firstAC==1){ | firstAC=0 | Prev1stAcLevel=PrevLevel | } | } | }while(scanPos<(1<<(log2BlkWidth+log2BlkHeight))) | } | ]]>

coeff_zero_run

specifies the number of zero-valued transform coefficient levels that are located before the position of the next non-zero transform coefficient level in a scan of transform coefficient levels.

abs_ac_coeff_minus1

plus 1 specifies the absolute value of an AC transform coefficient level at the given scanning position.

sign_ac_coeff

specifies the sign of an AC transform coefficient level for the given scanning position. sign_ac_coeff equal to 0 specifies that the corresponding AC transform coefficient level has a positive value. sign_ac_coeff equal to 1 specifies that the corresponding AC transform coefficient level has a negative value.

Byte alignment syntax

alignment_bit_equal_to_zero

MUST be equal to 0.

Decoding process This process is invoked to obtain a decoded frame from a bitstream. Input to this process is a bitstream of a Frame Data. Output of this process is a decoded frame. The decoding process operates as follows for the current frame:

The syntax structure for a Frame Data is parsed to obtain the parsed syntax structures.
The processes in , and specify the decoding processes using syntax elements in all syntax structures. It is the requirement of bitstream conformance that the coded tiles of the frame MUST contain tile data for every MB of the frame, such that the division of the frame into tiles and the division of the tiles into MBs each forms a partitioning of the frame.
After all the tiles in the current frame have been decoded, the decoded frame is cropped using the cropping rectangle if FrameWidthInSamplesY is not equal to FrameWidthInMbY * MbWidth or FrameHeightInSamplesY is not equal to FrameHeightInMbY * MbHeight.
The cropping rectangle, which specifies the samples of a frame that are output, is derived as follows.

- The cropping rectangle contains the luma samples with horizontal frame coordinates from 0 to FrameWidthInSampleY - 1 and vertical frame coordinates from 0 to FrameHeightInSampleY - 1, inclusive.

- The cropping rectangle contains the two chroma arrays having frame coordinates (x//SubWidthC, y//SubHeightC), where (x,y) are the frame coordinates of the specified luma samples.

MB decoding process This process is invoked for each MB. Input to this process is a luma location (xMb, yMb) specifying the top-left sample of the current luma MB relative to the top left luma sample of the current frame. Outputs of this process are the reconstructed samples of all the NumComp color components (when chorma_format_idc is equal to 2 or 3, Y, Cb, and Cr) for the current MB. The following steps applies:

Let recSamples[0] be a (MbWidth)x(MbHeight) array of the reconstructed samples of the first color component (when chroma_format_idc is equal to 2 or 3, Y).
The block reconstruction process as specified in is invoked with the luma location (xMb, yMb), the variable nBlkW set equal to MbWidth, the variable nBlkH set equal to MbHeight, the variable cIdx set equal to 0, and the (MbWidth)x(MbHeight) array recSamples[0] as inputs, the output is a modified version of the (MbWidth)x(MbHeight) array resSamples[0], which is the reconstructed samples of the first color component for the current MB.
Let recSamples[1] be a (MbWidthC)x(MbHeightC) array of the reconstructed samples of the second color component (when chroma_format_idc is equal to 2 or 3, Cb).
The block reconstruction process as specified in is invoked with the luma location (xMb, yMb), the variable nBlkW set equal to MbWidthC, the variable nBlkH set equal to MbHeightC, the variable cIdx set equal to 1, and the (MbWidthC)x(MbHeightC) array recSamples[1] as inputs, the output is a modified version of the (MbWidthC)x(MbHeightC) array recSamples[1], which is the reconstructed samples of the second color component for the current MB.
Let recSamples[2] be a (MbWidthC)x(MbHeightC) array of the reconstructed samples of the third color component(when chroma_format_idc is equal to 2 or 3, Cr).
The block reconstruction process as specified in is invoked with the luma location (xMb, yMb), the variable nBlkW set equal to MbWidthC, the variable nBlkH set equal to MbHeightC, the variable cIdx set equal to 2, and the (MbWidthC)x(MbHeightC) array recSamples[2] as inputs, the output is a modified version of the (MbWidthC)x(MbHeightC) array recSamples[2], which is the reconstructed samples of the third color component for the current MB.

Block reconstruction process Inputs to this process are:

a luma location (xMb, yMb) specifying the top-left sample of the current MB relative to the top left luma sample of the current frame,
two variables nBlkW and nBlkH specifying the width and the height of the current block,
a variable cIdx specifying the color componnet of the current block, and
an (nBlkW)x(nBlkH) array recSamples of reconstructed block.

Output of this process is a modified version of the (nBlkW)x(nBlkH) array recSamples of reconstructed samples. The following applies:

The variables numBlkX and numBlkY are derived as follows:

- - numBlkX = nBlkW // TrSize

- - numBlkY = nBlkH // TrSize

For yIdx = 0..numBlkY - 1, the following applies:

- - For xIdx = 0..numBlkX - 1, the following applies:

The variables xBlk and yBlk are derived as follows:

- - xBlk = xMb // (cIdx==0? 1: SubWidthC) + xIdx*TrSize

- - yBlk = yMb // (cIdx==0? 1: SubHeightC) + yIdx*TrSize

The scaling and transformation process as specified in is invoked with the location ( xBlk, yBlk ), the variable cIdx set equal to cIdx, the transform width nBlkW set equal to TrSize and the transform height nBlkH set equal to TrSize as inputs, and the output is a (TrSize)x(TrSize) array r of reconstructed block.
The (TrSize)x(TrSize) array recSamples is modified as follows:

- recSamples[(xIdxTrSize) + i, (yIdxTrSize) + j] = r[i,j], with i=0..TrSize-1, j=0..TrSize-1

Scaling and transformation process Inputs to this process are:

a location (xBlkY, yBlkY) of the current color component specifying the top-left sample of the current block relative to the top-left sample of the current frame,
a variable cIdx specifying the color component of the current block,
a variable nBlkW specifying the width of the current block, and
a variable nBlkH specifying the height of the current block.

Output of this process is the (nBlkW)x(nBlkH) array of reconstructed samples r with elements r[x][y]. The quantization parameter qP is derived as follows:

- qP = Qp[cIdx] + QpBdOffset

The (nBlKW)x(nBlkH) array of reconstructed samples r is derived as follows:

The scaling process for transform coefficients as specified in is invoked with the block location (xBlkY, yBlkY), the block width nBlkW and the block height nBlkH, the color component variable cIdx, and the quantization parameter qP as inputs, and the output is an (nBlkW)x(nBlkH) array of scaled transform coefficients d.
The transformation process for scaled transform coefficients as specified in is invoked with the block location (xBlkY, yBlkY), the block width nBlkW and the block height nBlkH, the color component variable cIdx, and the (nBlkW)x(nBlkH) array of scaled transform coefficients d as inputs, and the output is an (nBlkW)x(nBlkH) array of reconstructed samples r.
The variable bdShift is derived as follows:

- bdShift = 20 - BitDepth

The reconstructed sample values r[x][y] with x = 0..nBlkW - 1, y = 0..nBlkH - 1 are modified as follows:

- r[x][y] = clip(0, (1 << BitDepth)-1, ((r[x][y]+(1 << (bdShift-1)))>>bdShift) + (1 << (BitDepth-1)))

Scaling process for transform coefficients Inputs to this process are:

a location (xBlkY, yBlkY) of the current color component specifying the top-left sample of the current block relative to the top-left sample of the current frame,
a variable nBlkW specifying the width of the current block,
a variable nBlkH specifying the height of the current block,
a variable cIdx specifying the color component of the current block, and
a variable qP specifying the quantization parameter.

Output of this process is the (nBlkW)x(nBlkH) array d of scaled transform coefficients with elements d[x][y]. The variable bdShift is derived as follows:

- bdShift = BitDepth + ((Log2(nBlkW) + Log2(nBlkH)) // 2) - 5

The list levelScale[] is specified as follows:

- levelScale[k] = {40, 45, 51, 57, 64, 71} with k = 0..5.

For the derivation of the scaled transform coefficients d[x][y] with x = 0..nBlkW - 1, y = 0..nBlkH - 1, the following applies:

The scaled transform coefficient d[x][y] is derived as follows:

- d[x][y] = clip(-32768, 32767, ( ( TransCoeff[cIdx][xBlkY][yBlkY] * QMatrix[cIdx][x][y] * levelScale[qP%6] << (qP//6) ) + ( 1 << (bdShift-1) ) >> bdShift ))

Process for scaled transform coefficients

General Inputs to this process are:

a location (xBlkY, yBlkY) of the current color component specifying the top-left sample of the current block relative to the top-left sample of the current frame,
a variable nBlkW specifying the width of the current block,
a variable nBlkH specifying the height of the current block, and
an (nBlkW)x(nBlkH) array d of scaled transform coefficients with elements d[ x ][ y ].

Output of this process is the (nBlkW)x(nBlkH) array r of reconstructed samples with elements r[x][y]. The (nBlkW)x(nBlkH) array r of reconstructed samples is derived as follows:

Each (vertical) column of scaled transform coefficients d[x][y] with x = 0..nBlkW - 1, y = 0..nBlkH - 1 is transformed to e[x][y] with x = 0..nBlkW - 1, y = 0..nBlkH - 1 by invoking the one- dimensional transformation process as specified in for each column x = 0..nBlkW - 1 with the size of the transform block nBlkH, and the list d[x][y] with y = 0..nBlkH - 1 as inputs, and the output is the list e[x][y] with y = 0..nBlkH - 1.
The following applies:

- g[x][y] = (e[x][y] + 64) >> 7

Each (horizontal) row of the resulting array g[x][y] with x = 0..nBlkW - 1, y = 0..nBlkH - 1 is transformed to r[x][y] with x = 0..nBlkW - 1, y = 0..nBlkH - 1 by invoking the one-dimensional transformation process as specified in for each row y = 0..nBlkH - 1 with the size of the transform block nBlkW, and the list g[x][y] with x = 0..nBlkW - 1 as inputs, and the output is the list r[x][y] with x = 0..nBlkW - 1.

Transformation process Inputs to this process are:

a variable nTbS specifying the sample size of scaled transform coefficients, and
a list of scaled transform coefficients x with elements x[j], with j = 0..nTbS - 1.
Output of this process is the list of transformed samples y with elements y[i], with i = 0..nTbS - 1.
The transformation matrix derivation process as specified in . invoked with the transform size nTbS as input, and the transformation matrix transMatrix as output.
The list of transformed samples y[i] with i = 0..nTbS - 1 is derived as follows:

- y[i] = sum("j" =0,"nTbS" -1,transMatrix[ i][j]*x[j])

Transformation matrix derivation process Input to this process is a variable nTbS specifying the horizontal sample size of scaled transform coefficients. Output of this process is the transformation matrix transMatrix. The transformation matrix transMatrix is derived based on nTbs as follows:

If nTbs is equal to 8, the following applies:

Parsing process

Process for syntax element type h(v) This process is invoked for the parsing of syntax elements with descriptor h(v) in and .

Process for abs_dc_coeff_diff Inputs to this process are bits for the abs_dc_coeff_diff syntax element. Output of this process is a value of the abs_dc_coeff_diff syntax element. The variable kParam is derived as follows:

- kParam = clip( 0, 5, PrevDcDiff >> 1 )

The value of syntax element abs_dc_coeff_diff is obtained by invoking the parsing process for variable length codes as specified in with kParam.

Process for coeff_zero_run Inputs to this process are bits for the coeff_zero_run syntax element. Output of this process is a value of the coeff_zero_run syntax element. The variable kParam is derived as follows:

- kParam = clip( 0, 2, PrevRun >> 2 )

The value of syntax element coeff_zero_run is obtained by invoking the parsing process for variable length codes as specified in with kParam.

Process for abs_ac_coeff_minus1 Inputs to this process are bits for the abs_ac_coeff_minus1 syntax element. Output of this process is a value of the abs_ac_coeff_minus1 syntax element. The variable kParam is derived as follows:

- kParam = clip( 0, 4, PrevLevel >> 2 )

The value of syntax element abs_ac_coeff_minus1 is obtained by invoking the parsing process for variable length codes as specified in with kParam.

Process for variable length codes Input to this process is kParam. Output of this process is a value, symbolValue, of a syntax element. The symbolValue is derived as follows: 0) symbolValue += read_bits(k) ]]> where the value returned from read_bits(n) is interpreted as a binary representation of a n-bit unsigned integer with most significant bit written first.

Codeword generation process for h(v) (informative) This process specifies the code generation process for syntax elements with descriptor h(v) in sections between 7.1.1. and 7.1.3.

Process for abs_dc_coeff_diff Input to this process is a symbol value of the abs_dc_coeff_diff syntax element. Output of this process is a codeword of the abs_dc_coeff_diff syntax element. The variable kParam is derived as follows:

- kParam = clip( 0, 5, PrevDcDiff >> 1 )

The codeword of syntax element abs_dc_coeff_diff is obtained by invoking the generation process for variable length codes as specified in with the symbol value symbolValue and kParam.

Process for coeff_zero_run Input to this process is a symbol value of the coeff_zero_run syntax element. Output of this process is a codeword of the coeff_zero_run syntax element. The variable kParam is derived as follows:

- kParam = clip( 0, 2, PrevRun >> 2 )

The codeword of syntax element coeff_zero_run is obtained by invoking the generation process for variable length codes as specified in with the symbol value symbolValue and kParam.

Process for abs_ac_coeff_minus1 Input to this process is a symbol value of the abs_ac_coeff_minus1 syntax element. Output of this process is a codeword of the abs_ac_coeff_minus1 syntax element. The variable kParam is derived as follows:

- kParam = clip( 0, 4, PrevLevel >> 2 )

The codeword of syntax element abs_ac_coeff_minus1 is obtained by invoking the generation for variable length codes as specified in with the symbol value symbolValue and kParam.

Process for variable length codes Inputs to this process are

symbolVal and
kParam.

Output of this process is a codeword of a syntax element. The codeword is derived as follows: > kParam) bitCount = 0 k = kParam while(symbolValue >= (1 << k)) { symbolValue -= (1 << k) if(bitCount < 2) put_bits(SimpleVLCTable[valSimpleVLC][ bitCount ], 1) else put_bits(0, 1) if(bitCount >= 2) k++ bitCount++ } if(bitCount < 2) put_bits(SimpleVLCTable[valSimpleVLC][ bitCount ], 1) else put_bits(1, 1) if(k > 0) put_bits(symbolValue, k) ]]> where a codeword generated from put_bits( v, n ) is interpreted as a binary representation of an n-bit unsigned integer value v with most significant bit written first.

Security Considerations APV decoder should take appropriate security considerations into account. A decoder MUST be robust against any non-compliant or malicious payloads.

IANA Considerations This document has no actions for IANA.

Appendix

Appendix A

Overview of profiles, levels and toolsets Profiles and levels specify restrictions on the bitstreams and hence limits on the capabilities needed to decode the bitstreams. Profiles and levels may also be used to indicate interoperability points between individual decoder implementations. NOTE This document does not include individually selectable "options" at the decoder, as this would increase interoperability difficulties. Each profile specifies a subset of algorithmic features and limits that MUST be supported by all decoders conforming to that profile. NOTE Encoders are not required to make use of any particular subset of features supported in a profile. Each level specifies a set of limits on the values that may be taken by the syntax elements of this document. The same set of level definitions is used with all profiles, but individual implementations may support a different level for each supported profile. For any given profile, a level generally corresponds to a particular decoder processing load and memory capability. The profiles that are specified in are also referred to as the profiles specified in

Requirements on video decoder capability Capabilities of video decoders conforming to this document are specified in terms of the ability to decode video streams conforming to the constraints of profiles and levels specified in this section. When expressing the capabilities of a decoder for a specified profile, the level supported for that profile should also be expressed. Specific values are specified in this section for the syntax elements profile__idc and level__idc. All other values of profile_idc and level_idc are reserved for future use. NOTE Decoders must not infer that a reserved value of profile__idc between the values specified in this document indicates intermediate capabilities between the specified profiles, as there are no restrictions on the method to be chosen for the use of such future reserved values. However, decoders must infer that a reserved value of level__idc between the values specified in this document indicates intermediate capabilities between the specified levels.

Profiles

General All constraints for Frame Datas that are specified are constraints for Frame Datas that are activated when the bitstream is decoded.

Baseline profile Conformance of a bitstream to the Baseline profile is indicated by profile_idc equal to 33. Bitstreams conforming to the Baseline profile MUST obey the following constraints: + chroma_format_idc MUST be equal to 2. + bit_depth_minus8 MUST be in the range of 2 to 4. The level constraints specified for the Baseline profile in . MUST be fulfilled. Decoders conforming to the Baseline profile at a specific level (identified by a specific value of L) MUST be capable of decoding all bitstreams for which all of the following conditions apply: + The bitstream is indicated to conform to the Baseline profile. + The bitstream is indicated to conform to a level (by a specific value of level_idc) that is lower than or equal to level L.

Levels

General level limits For purposes of comparison of level capabilities, a particular level is considered to be a lower level than some other level when the value of the level_idc of the particular level is less than that of the other level. + FrameSizeInSamplesY MUST be less than or equal to MaxLumaSr, where MaxLumaSr is specified in Table 3. + The luma sample rate (luma samples per second) MUST be less than or equal to MaxLumaSr. + The coded data rate (bits per second) MUST be less than or equal to MaxCodedDr. + The value of tile_width_in_mbs_minus1 MUST be greater than or equal to 15. + The value of tile_height_in_mbs_minus1 MUST be greater than or equal to 7. + The value of TileCols MUST be less than or equal to 20. + The value of TileRows MUST be less than or equal to 20. specifies the limits for each level. A level to which a bitstream conforms is indicated by the syntax element level_idc as follows:

level_idc MUST be set equal to a value of 30 times the level number specified in .

General level limits

level	Max luma sample rate (sample/sec)	Max coded data rate (bits/sec)
1	70,778,880	200,400,000
1.1	141,557,760	400,800,000
2	267,386,880	780,000,000
2.1	534,773,760	1,560,000,000
3	1,069,547,520	3,324,000,000
3.1	2,139,095,040	6,648,000,000
4	4,278,190,080	13,296,000,000
4.1	8,556,380,160	26,592,000,000
5	17,112,760,320	53,184,000,000
5.1	34,225,520,640	106,368,000,000

Appendix B

Raw bitstream Frame Data syntax and semantics

Raw bitstream Frame Data syntax

frame_data_size

indicates the length of the Frame Data, in bytes, within the frame_data( ) syntax structure.