Advance Professional Video
draft-lim-apv-00
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Youngkwon Lim , Minwoo Park , Madhukar Budagavi , Rajan Joshi , Kwang Pyo Choi | ||
| Last updated | 2024-03-01 | ||
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draft-lim-apv-00
Independent Submission Y. Lim
Internet-Draft M. Park
Intended status: Informational M. Budagavi
Expires: 2 September 2024 R. Joshi
K. Choi
Samsung Electronics
1 March 2024
Advance Professional Video
draft-lim-apv-00
Abstract
This document describes bitstream format of Advanced Professional
Video and decoding process of it.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 2 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Terms and definitions . . . . . . . . . . . . . . . . . . 4
2.2. Abbreviated terms . . . . . . . . . . . . . . . . . . . . 6
3. Conventions used in this document . . . . . . . . . . . . . . 6
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Operators . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Arithmetic operators . . . . . . . . . . . . . . . . 7
3.2.2. Bitwise operators . . . . . . . . . . . . . . . . . . 7
3.3. Range notation . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Order of operations precedence . . . . . . . . . . . 8
3.4. Variables, syntax elements and tables . . . . . . . . . . 9
3.5. Processes . . . . . . . . . . . . . . . . . . . . . . . . 11
4. Formats and processes used in this document . . . . . . . . . 11
4.1. Bitstream formats . . . . . . . . . . . . . . . . . . . . 11
4.2. Source, decoded and output frame formats . . . . . . . . 11
4.3. Partitioning of a frame . . . . . . . . . . . . . . . . . 14
4.3.1. Partitioning of a frame into tiles . . . . . . . . . 14
4.3.2. Spatial or component-wise partitioning . . . . . . . 15
4.4. Scanning processes . . . . . . . . . . . . . . . . . . . 15
4.4.1. Zig-zag scan . . . . . . . . . . . . . . . . . . . . 15
4.4.2. Inverse scan . . . . . . . . . . . . . . . . . . . . 16
5. Syntax and semantics . . . . . . . . . . . . . . . . . . . . 17
5.1. Method of specifying syntax . . . . . . . . . . . . . . . 17
5.2. Syntax functions and descriptors . . . . . . . . . . . . 17
5.2.1. byte_aligned() . . . . . . . . . . . . . . . . . . . 18
5.2.2. more_data_in_tile() . . . . . . . . . . . . . . . . . 18
5.2.3. next_bits(n) . . . . . . . . . . . . . . . . . . . . 18
5.2.4. read_bits(n) . . . . . . . . . . . . . . . . . . . . 18
5.2.5. Syntax element processing functions . . . . . . . . . 18
5.3. List of syntax . . . . . . . . . . . . . . . . . . . . . 19
5.3.1. Frame Data . . . . . . . . . . . . . . . . . . . . . 19
5.3.2. Frame header syntax . . . . . . . . . . . . . . . . . 19
5.3.3. Quantization matrix syntax . . . . . . . . . . . . . 23
5.3.4. Tile info syntax . . . . . . . . . . . . . . . . . . 23
5.3.5. Metadata syntax . . . . . . . . . . . . . . . . . . . 25
5.3.6. Filler data syntax . . . . . . . . . . . . . . . . . 25
5.3.7. Tile syntax . . . . . . . . . . . . . . . . . . . . . 25
5.3.8. Tile header syntax . . . . . . . . . . . . . . . . . 26
5.3.9. Tile data syntax . . . . . . . . . . . . . . . . . . 27
5.3.10. Macroblock layer syntax . . . . . . . . . . . . . . . 27
5.3.11. AC coefficient coding syntax . . . . . . . . . . . . 28
5.3.12. Byte alignment syntax . . . . . . . . . . . . . . . . 30
6. Decoding process . . . . . . . . . . . . . . . . . . . . . . 30
6.1. MB decoding process . . . . . . . . . . . . . . . . . . . 31
6.2. Block reconstruction process . . . . . . . . . . . . . . 32
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6.3. Scaling and transformation process . . . . . . . . . . . 33
6.3.1. Scaling process for transform coefficients . . . . . 34
6.3.2. Process for scaled transform coefficients . . . . . . 35
7. Parsing process . . . . . . . . . . . . . . . . . . . . . . . 36
7.1. Process for syntax element type h(v) . . . . . . . . . . 37
7.1.1. Process for abs_dc_coeff_diff . . . . . . . . . . . . 37
7.1.2. Process for coeff_zero_run . . . . . . . . . . . . . 37
7.1.3. Process for abs_ac_coeff_minus1 . . . . . . . . . . . 37
7.1.4. Process for variable length codes . . . . . . . . . . 38
7.2. Codeword generation process for h(v) (informative) . . . 39
7.2.1. Process for abs_dc_coeff_diff . . . . . . . . . . . . 39
7.2.2. Process for coeff_zero_run . . . . . . . . . . . . . 39
7.2.3. Process for abs_ac_coeff_minus1 . . . . . . . . . . . 39
7.2.4. Process for variable length codes . . . . . . . . . . 40
8. Security Considerations . . . . . . . . . . . . . . . . . . . 41
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
10. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 41
10.1. Appendix A . . . . . . . . . . . . . . . . . . . . . . . 41
10.1.1. Overview of profiles, levels and toolsets . . . . . 41
10.1.2. Requirements on video decoder capability . . . . . . 41
10.1.3. Profiles . . . . . . . . . . . . . . . . . . . . . . 42
10.1.4. Levels . . . . . . . . . . . . . . . . . . . . . . . 42
10.2. Appendix B . . . . . . . . . . . . . . . . . . . . . . . 43
10.2.1. Raw bitstream Frame Data syntax and semantics . . . 43
11. Normative References . . . . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44
1. 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
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* 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
2. Terms
2.1. 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
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* 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
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* 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
2.2. Abbreviated terms
* I: intra
* LSB: least significant bit
* MSB: most significant bit
* RGB: Red, Green and Blue
3. Conventions used in this document
3.1. 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
[RFC2119].
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3.2. Operators
The operators and the order of precedence are the same as used in the
C programming language [ISO9899-2018], with the exception of the
operators described in the Section 3.2.1 and Section 3.2.2
3.2.1. 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
3.2.2. 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.
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* 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.
3.3. 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
3.3.1. 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. Table 1 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.
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+=========================================+
| 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" |
+-----------------------------------------+
Table 1: Operation precedence from
highest (top of the table) to lowest
(bottom of the table)
3.4. 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
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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 Section 5.2 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.
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3.5. 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.
4. Formats and processes used in this document
4.1. 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.
4.2. 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).
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* 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
Table 2, 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.
+===================+==========+===========+============+==========+
| chroma_format_idc | Chroma | SubWidthC | SubHeightC | NumpComp |
| | format | | | |
+===================+==========+===========+============+==========+
| 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 |
+-------------------+----------+-----------+------------+----------+
Table 2: SubWidthC, SubHeightC and NumComp values derived from
chroma_format_idc
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 Figure 1.
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& * & * & * & * & * ...
& * & * & * & * & * ...
& * & * & * & * & * ...
& * & * & * & * & * ...
...
& - location where both luma and chroma sample exist
* - location where only luma sample exist
Figure 1: 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 Figure 2.
& & & & & & & & & & ...
& & & & & & & & & & ...
& & & & & & & & & & ...
& & & & & & & & & & ...
...
& - location where both luma and chroma sample exist
Figure 2: 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
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* MbHeightC = MbHeight // SubHeightC
4.3. Partitioning of a frame
4.3.1. 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.
+===================+===================+=========+
# | | | # MB | MB | MB | MB # MB | MB #
+-------------------+-------------------+---------+
# | | | # MB | MB | MB | MB # MB | MB #
+----- tile -----+-------------------+---------+
# | | | # MB | MB | MB | MB # MB | MB #
+-------------------+-------------------+---------+
# | | | # MB | MB | MB | MB # MB | MB #
+===================+===================+=========+
# MB | MB | MB | MB # MB | MB | MB | MB # MB | MB #
+-------------------+-------------------+---------+
# MB | MB | MB | MB # MB | MB | MB | MB # MB | MB #
+-------------------+-------------------+---------+
# MB | MB | MB | MB # MB | MB | MB | MB # MB | MB #
+-------------------+-------------------+---------+
# MB | MB | MB | MB # MB | MB | MB | MB # MB | MB #
+===================+===================+=========+
#,= tile boundary
|,- MB boundary
Figure 3: Frame with 10 by 8 MBs that is partitioned into 6 tiles
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4.3.2. 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.
4.4. Scanning processes
4.4.1. 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:
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pos=0
zigZagScan[pos]=0
pos++
for(line=1;line<(blkWidth+blkHeight-1);line++){
if(line%2){
x=min(line,blkWidth-1)
y=max(0,line-(blkWidth-1))
while(x>=0&&y<blkHeight){
zigZagScan[pos]=y*blkWidth+x
pos++
x--
y++
}
}
else{
y=min(line,blkHeight-1)
x=max(0,line-(blkHeight-1))
while(y>=0&&x<blkWidth){
zigZagScan[pos]=y*blkWidth+x
pos++
x++
y--
}
}
}
Figure 4: Pseudo-code for zig-zag scan
4.4.2. 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 Section 4.4.1 with
input parameters blkWidth and blkHeight.
* The output variable inverseScan is derived as follows:
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for(pos=0;pos<blkWidth*blkHeight;pos++){
inverseScan[forwardScan[pos]]=pos
}
Figure 5: Pseudo-code for inverse zig-zag scan
5. Syntax and semantics
5.1. 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 [ISO9899-2018] 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 Figure 6. 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 Section 5.2.5
syntax code | type
--------------------------------------------------------------|-----
ExampleSyntaxCode( ) { |
operations |
syntax_element | u(n)
} |
Figure 6: A depiction of type-labeled syntax code for syntax
description in this document
5.2. 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.
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5.2.1. 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.
5.2.2. 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.
5.2.3. 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.
5.2.4. 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.
5.2.5. 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.
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* h(v): variable-length entropy coded syntax element with the left
bit first. The parsing process for this descriptor is specified
in Section 7.1.
5.3. List of syntax
5.3.1. Frame Data
syntax code | type
--------------------------------------------------------|--------
frame_data(){ |
frame_header() |
for(tileIdx=0;tileIdx<NumTiles;tileIdx++){ |
tile_size_minus1[tileIdx] | u(32)
tile(tileIdx) |
} |
metadata() |
filler_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
5.3.2. Frame header syntax
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syntax code | type
---------------------------------------------------|-------
frame_header(){ |
frame_header_size | u(16)
profile_idc | u(8)
level_idc | u(8)
reserved_zero_8bits | u(8)
frame_width_minus1 | u(32)
frame_height_minus1 | u(32)
chroma_format_idc | u(4)
bit_depth_minus8 | u(4)
capture_time_distance | u(8)
reserved_zero_16bits | u(16)
color_description_present_flag | u(1)
if(color_description_present_flag){ |
color_primaries | u(8)
transfer_characteristics | u(8)
matrix_coefficients | u(8)
} |
use_q_matrix | u(1)
if(use_q_matrix){ |
quantization_matrix() |
} |
tile_info() |
reserved_zero_8bits | u(8)
byte_alignment() |
} |
* 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 Section 10.1. 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 Section 10.1. Other
values of level_idc are reserved for future use.
* reserved_zero_8bits
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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 Section 10.1. 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 Table 2 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
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specifies the bit depth of the samples. The variables BitDepth
and QpBdOffset are derived as follows:
o BitDepth = bit_depth_minus8 + 8
o 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 Section 10.1 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
[ISO23091-2]. 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
[ISO23091-2]. When the transfer_characteristics syntax element is
not present, the value of transfer_characteristics is inferred to
be equal to 2.
* matrix_coefficients
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MUST have the semnatics of MatrixCoefficients as specified in
[ISO23091-2]. 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 Section 10.1 MUST ignore Frame Data with values of
reserved_zero_8bits greater than 0.
5.3.3. Quantization matrix syntax
syntax code | type
---------------------------------------------------|--------
quantization_matrix(){ |
for(cIdx=0;cIdx<NumComp;cIdx++){ |
for(y=0;y<8;y++){ |
for(x=0;x<8;x++){ |
q_matrix_minus1[cIdx][x][y] | u(8)
} |
} |
} |
} |
* 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
5.3.4. Tile info syntax
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syntax code | type
---------------------------------------------------|-------
tile_info(){ |
tile_width_in_mbs_minus1 | u(28)
tile_height_in_mbs_minus1 | u(28)
startMb=0 |
for(i=0;startMb<FrameWidthInMbsY;i++){ |
ColStarts[i]=startMb*MbWidth |
startMb+=tile_width_in_mbs_minus1+1 |
} |
ColStarts[i]=FrameWidthInMbsY*MbWidth |
TileCols=i |
startMb=0 |
for(i=0;startMb<FrameHeightMbsY;i++){ |
RowStarts[i]=startMb*MbHeight |
startMb+=tile_height_in_mbs_minus1+1 |
} |
RowStarts[i]=FrameHeightMbsY*MbHeight |
TileRows=i |
NumTiles=TileCols*TileRows |
tile_size_present_in_fh_flag | u(1)
if(tile_size_present_in_fh_flag){ |
for(tileIdx=0;tileIdx<NumTiles;tileIdx++){ |
tile_size_in_fh_minus1[tileIdx] | u(32)
} |
} |
} |
* 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
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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].
5.3.5. Metadata syntax
syntax code | type
---------------------------------------------------|-------
metadata(){ |
metadata_size | u(32)
metadata_payload(metadata_size) |
} |
* metadata_size
specifies the size of metadata in current Frame Data. Syntax and
semantics of metadata_payload() is not defined in this document.
5.3.6. Filler data syntax
syntax code | type
---------------------------------------------------|-------
filler_data(){ |
while(next_bits(8)==0xFF) |
ff_byte | f(8)
} |
* ff_byte
is a byte equal to 0xFF.
5.3.7. Tile syntax
syntax code | type
---------------------------------------------------|-------
tile(tileIdx){ |
tile_header() |
for(i=0;i<NumComp;i++){ |
tile_data(tileIdx,i) |
} |
while(more_data_in_tile()){ |
tile_dummy_byte | b(8)
} |
} |
* tile_dummy_byte
has any pattern of 8-bit string.
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5.3.8. Tile header syntax
syntax code | type
---------------------------------------------------|-------
tile_header(){ |
tile_header_size | u(16)
tile_index | u(16)
for(i=0;i<NumComp;i++){ |
tile_data_size_minus1[i] | u(32)
} |
for(i=0;i<NumComp;i++){ |
tile_qp[i] | u(8)
} |
reserved_zero_8bits | u(8)
byte_alignment() |
} |
* 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
o Qp[i] = tile_qp[i] - QpBdOffset
o Qp[i] MUST be in the range of -QpBdOffset to 51, inclusive.
* reserved_zero_8bits
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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 Section 10.1 MUST ignore Frame Data with values of
reserved_zero_8bits greater than 0.
5.3.9. Tile data syntax
syntax code | type
----------------------------------------------------|-------
tile_data(tileIdx,cIdx){ |
x0=ColStarts[tileIdx%TileCols] |
y0=RowStarts[tileIdx//TileCols] |
numMbColsInTile=(ColStarts[tileIdx%TileCols+1]- |
ColStarts[tileIdx%TileCols])//MbWidth |
numMbRowsInTile=(RowStarts[tileIdx//TileCols+1]- |
RowStarts[tileIdx//TileCols])//MbHeight |
numMbsInTile=numMbColsInTile*numMbRowsInTile |
PrevDC=0 |
PrevDcDiff=20 |
Prev1stAcLevel=0 |
for(i=0;i<numMbsInTile;i++){ |
xMb=x0+((i%numMbColsInTile)*MbWidth) |
yMb=y0+((i//numMbColsInTile)*MbHeight) |
macroblock_layer(xMb,yMb,cIdx) |
} |
byte_alignment() |
} |
5.3.10. Macroblock layer syntax
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syntax code | type
----------------------------------------------------|-------
macroblock_layer(xMb,yMb,cIdx){ |
subW=(cIdx==0)?1:SubWidthC |
subH=(cIdx==0)?1:SubHeightC |
blkWidth=(cIdx==0)?MbWidth:MbWidthC |
blkHeight=(cIdx==0)?MbHeight:MbHeightC |
TrSize=8 |
for(y=0;y<blkHeight;y+=TrSize){ |
for(x=0;x<blkWidth;x+=TrSize){ |
abs_dc_coeff_diff | h(v)
if(abs_dc_coeff_diff) |
sign_dc_coeff_diff | u(1)
TransCoeff[cIdx][xMb//subW+x][yMb//subH+y]= |
PrevDC+abs_dc_coeff_diff |
*(1-2*sign_dc_coeff_diff) |
PrevDC= |
TransCoeff[cIdx][xMb//subW+x][yMb//subH+y] |
PrevDcDiff=abs_dc_coeff_diff |
ac_coeff_coding(xMb//subW+x,yMb//subH+y, |
Log2(TrSize),Log2(TrSize),cIdx) |
} |
} |
} |
* 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.
5.3.11. AC coefficient coding syntax
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syntax code | type
----------------------------------------------------|-------
ac_coeff_coding(x0,y0,log2BlkWidth, |
log2BlkHeight,cIdx){ |
scanPos=1 |
firstAC=1 |
PrevLevel=Prev1stAcLevel |
PrevRun=0 |
do{ |
coeff_zero_run | h(v)
for(i=0;i<coeff_zero_run;i++){ |
blkPos=ScanOrder[scanPos] |
xC=blkPos&((1<<log2BlkWidth)-1) |
yC=blkPos>>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)-1) |
yC=blkPos>>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.
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* 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.
5.3.12. Byte alignment syntax
syntax code | type
---------------------------------------------------|-------
byte_alignment(){ |
while(!byte_aligned()) |
alignment_bit_equal_to_zero | f(1)
} |
* alignment_bit_equal_to_zero
MUST be equal to 0.
6. 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 Section 6.1, Section 6.2 and Section 6.3 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.
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- 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.
6.1. 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 Section 6.2 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 Section 6.2 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.
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* 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 Section 6.2 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.
6.2. 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:
o numBlkX = nBlkW // TrSize
o numBlkY = nBlkH // TrSize
* For yIdx = 0..numBlkY - 1, the following applies:
o For xIdx = 0..numBlkX - 1, the following applies:
The variables xBlk and yBlk are derived as follows:
o xBlk = xMb // (cIdx==0? 1: SubWidthC) + xIdx*TrSize
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o yBlk = yMb // (cIdx==0? 1: SubHeightC) + yIdx*TrSize
* The scaling and transformation process as specified in Section 6.3
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[(xIdx_TrSize) + i, (yIdx_TrSize) + j] = r[i,j], with
i=0..TrSize-1, j=0..TrSize-1
6.3. 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
Section 6.3.1 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 Section 6.3.2 is invoked with the block location
(xBlkY, yBlkY), the block width nBlkW and the block height nBlkH,
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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)))
6.3.1. 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:
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d[x][y] = clip(-32768, 32767, ( (
TransCoeff[cIdx][xBlkY][yBlkY] * QMatrix[cIdx][x][y] *
levelScale[qP%6] << (qP//6) ) + ( 1 << (bdShift-1) ) >> bdShift
))
6.3.2. Process for scaled transform coefficients
6.3.2.1. 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 Section 6.3.2.2
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 Section 6.3.2.2 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.
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6.3.2.2. 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
Section 6.3.2.3. 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])
6.3.2.3. 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:
transMatrix[ m ][ n ] =
{
{ 64, 64, 64, 64, 64, 64, 64, 64 }
{ 89, 75, 50, 18, -18, -50, -75, -89 }
{ 84, 35, -35, -84, -84, -35, 35, 84 }
{ 75, -18, -89, -50, 50, 89, 18, -75 }
{ 64, -64, -64, 64, 64, -64, -64, 64 }
{ 50, -89, 18, 75, -75, -18, 89, -50 }
{ 35, -84, 84, -35, -35, 84, -84, 35 }
{ 18, -50, 75, -89, 89, -75, 50, -18 }
}
7. Parsing process
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7.1. Process for syntax element type h(v)
This process is invoked for the parsing of syntax elements with
descriptor h(v) in Section 5.3.10 and Section 5.3.11.
7.1.1. 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
Section 7.1.4 with kParam.
7.1.2. 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
Section 7.1.4 with kParam.
7.1.3. 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 Section 7.1.4 with kParam.
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7.1.4. 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:
symbolValue = 0
parseExpGolomb = 1
k = kParam
stopLoop = 0
if(read_bits(1) = = 1) {
parseExpGolomb = 0
}
else { (9 4)
if(read_bits (1) = = 0) {
symbolValue += (1 << k)
parseExpGolomb = 0
}
else {
symbolValue += (2 << k)
parseExpGolomb = 1
}
}
if(parseExpGolomb) {
do {
if(read_bits(1) = = 1) {
stopLoop = 1
}
else {
symbolValue += (1 << k)
k++
}
} while(!stopLoop)
}
if(k > 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.
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7.2. 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.
7.2.1. 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 Section 7.2.4 with the symbol value symbolValue and
kParam.
7.2.2. 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
Section 7.2.4 with the symbol value symbolValue and kParam.
7.2.3. 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:
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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
Section 7.2.4 with the symbol value symbolValue and kParam.
7.2.4. 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:
SimpleVLCTable[3][2] = { {1, 0}, {0, 0}, {0, 1} }
symbolValue = symbolVal
valSimpleVLC = clip(0, 2, symbolVal >> 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.
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8. Security Considerations
APV decoder should take appropriate security considerations into
account. A decoder MUST be robust against any non-compliant or
malicious payloads.
9. IANA Considerations
This document has no actions for IANA.
10. Appendix
10.1. Appendix A
10.1.1. 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 Section 10.1.3 are also referred to as
the profiles specified in Section 10.1
10.1.2. 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.
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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.
10.1.3. Profiles
10.1.3.1. General
All constraints for Frame Datas that are specified are constraints
for Frame Datas that are activated when the bitstream is decoded.
10.1.3.1.1. 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
Section 10.1.4. 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.
10.1.4. Levels
10.1.4.1. 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.
Table 3 specifies the limits for each level. A level to which a
bitstream conforms is indicated by the syntax element level_idc as
follows:
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* level_idc MUST be set equal to a value of 30 times the level
number specified in Table 3.
+=======+===================================+=================+
| 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 |
+-------+-----------------------------------+-----------------+
Table 3: General level limits
10.2. Appendix B
10.2.1. Raw bitstream Frame Data syntax and semantics
syntax code | type
--------------------------------------------------------------|-----
raw_bitstream_frame_data( ) { |
frame_data_size | u(32)
frame_data( ) |
} |
Figure 7: Raw bitstream Frame Data syntax
* frame_data_size
indicates the length of the Frame Data, in bytes, within the
frame_data( ) syntax structure.
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11. Normative References
[ISO23091-2]
"Recommendation ITU-T H.273 | ISO/IEC 23091-2, Information
technology — Coding-independent code points — Part 2
Video", n.d., <https://www.iso.org/standard/81546.html>.
[ISO9899-2018]
"International Organization for Standardization,
"Information technology - Programming languages - C", ISO/
IEC 9899:2018, June 2018.", n.d.,
<https://www.iso.org/standard/74528.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
Authors' Addresses
Youngkwon Lim
Samsung Electronics
6105 Tennyson Pkwy, Ste 300
Plano, TX, 75024
United States of America
Email: yklwhite@gmail.com
Minwoo Park
Samsung Electronics
34, Seongchon-gil, Seocho-gu
Seoul
3573
Republic of Korea
Email: m.w.park@samsung.com
Madhukar Budagavi
Samsung Electronics
6105 Tennyson Pkwy, Ste 300
Plano, TX, 75024
United States of America
Email: m.budagavi@samsung.com
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Rajan Joshi
Samsung Electronics
11488 Tree Hollow Ln
San Diego, CA, 92128
United States of America
Email: rajan_joshi@ieee.org
Kwang Pyo Choi
Samsung Electronics
11 Byeoryang-ro
Gwacheon
13839
Republic of Korea
Email: kwangpyo.choi@gmail.com
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