cellar M. Niedermayer
Internet-Draft
Intended status: Informational D. Rice
Expires: 27 November 2020
J. Martinez
26 May 2020
FFV1 Video Coding Format Version 0, 1, and 3
draft-ietf-cellar-ffv1-14
Abstract
This document defines FFV1, a lossless intra-frame video encoding
format. FFV1 is designed to efficiently compress video data in a
variety of pixel formats. Compared to uncompressed video, FFV1
offers storage compression, frame fixity, and self-description, which
makes FFV1 useful as a preservation or intermediate video format.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Notation and Conventions . . . . . . . . . . . . . . . . . . 5
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1. Pseudo-code . . . . . . . . . . . . . . . . . . . . . 6
2.2.2. Arithmetic Operators . . . . . . . . . . . . . . . . 6
2.2.3. Assignment Operators . . . . . . . . . . . . . . . . 6
2.2.4. Comparison Operators . . . . . . . . . . . . . . . . 7
2.2.5. Mathematical Functions . . . . . . . . . . . . . . . 7
2.2.6. Order of Operation Precedence . . . . . . . . . . . . 8
2.2.7. Range . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.8. NumBytes . . . . . . . . . . . . . . . . . . . . . . 8
2.2.9. Bitstream Functions . . . . . . . . . . . . . . . . . 8
3. Sample Coding . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Border . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Samples . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Median Predictor . . . . . . . . . . . . . . . . . . . . 10
3.4. Context . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5. Quantization Table Sets . . . . . . . . . . . . . . . . . 12
3.6. Quantization Table Set Indexes . . . . . . . . . . . . . 12
3.7. Color spaces . . . . . . . . . . . . . . . . . . . . . . 12
3.7.1. YCbCr . . . . . . . . . . . . . . . . . . . . . . . . 13
3.7.2. RGB . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.8. Coding of the Sample Difference . . . . . . . . . . . . . 15
3.8.1. Range Coding Mode . . . . . . . . . . . . . . . . . . 15
3.8.2. Golomb Rice Mode . . . . . . . . . . . . . . . . . . 20
4. Bitstream . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1. Parameters . . . . . . . . . . . . . . . . . . . . . . . 26
4.1.1. version . . . . . . . . . . . . . . . . . . . . . . . 28
4.1.2. micro_version . . . . . . . . . . . . . . . . . . . . 28
4.1.3. coder_type . . . . . . . . . . . . . . . . . . . . . 29
4.1.4. state_transition_delta . . . . . . . . . . . . . . . 29
4.1.5. colorspace_type . . . . . . . . . . . . . . . . . . . 30
4.1.6. chroma_planes . . . . . . . . . . . . . . . . . . . . 30
4.1.7. bits_per_raw_sample . . . . . . . . . . . . . . . . . 31
4.1.8. log2_h_chroma_subsample . . . . . . . . . . . . . . . 31
4.1.9. log2_v_chroma_subsample . . . . . . . . . . . . . . . 31
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4.1.10. extra_plane . . . . . . . . . . . . . . . . . . . . . 31
4.1.11. num_h_slices . . . . . . . . . . . . . . . . . . . . 32
4.1.12. num_v_slices . . . . . . . . . . . . . . . . . . . . 32
4.1.13. quant_table_set_count . . . . . . . . . . . . . . . . 32
4.1.14. states_coded . . . . . . . . . . . . . . . . . . . . 32
4.1.15. initial_state_delta . . . . . . . . . . . . . . . . . 32
4.1.16. ec . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.1.17. intra . . . . . . . . . . . . . . . . . . . . . . . . 33
4.2. Configuration Record . . . . . . . . . . . . . . . . . . 34
4.2.1. reserved_for_future_use . . . . . . . . . . . . . . . 34
4.2.2. configuration_record_crc_parity . . . . . . . . . . . 34
4.2.3. Mapping FFV1 into Containers . . . . . . . . . . . . 34
4.3. Frame . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.4. Slice . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.5. Slice Header . . . . . . . . . . . . . . . . . . . . . . 38
4.5.1. slice_x . . . . . . . . . . . . . . . . . . . . . . . 38
4.5.2. slice_y . . . . . . . . . . . . . . . . . . . . . . . 38
4.5.3. slice_width . . . . . . . . . . . . . . . . . . . . . 38
4.5.4. slice_height . . . . . . . . . . . . . . . . . . . . 38
4.5.5. quant_table_set_index_count . . . . . . . . . . . . . 39
4.5.6. quant_table_set_index . . . . . . . . . . . . . . . . 39
4.5.7. picture_structure . . . . . . . . . . . . . . . . . . 39
4.5.8. sar_num . . . . . . . . . . . . . . . . . . . . . . . 39
4.5.9. sar_den . . . . . . . . . . . . . . . . . . . . . . . 40
4.6. Slice Content . . . . . . . . . . . . . . . . . . . . . . 40
4.6.1. primary_color_count . . . . . . . . . . . . . . . . . 40
4.6.2. plane_pixel_height . . . . . . . . . . . . . . . . . 41
4.6.3. slice_pixel_height . . . . . . . . . . . . . . . . . 41
4.6.4. slice_pixel_y . . . . . . . . . . . . . . . . . . . . 41
4.7. Line . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.7.1. plane_pixel_width . . . . . . . . . . . . . . . . . . 41
4.7.2. slice_pixel_width . . . . . . . . . . . . . . . . . . 42
4.7.3. slice_pixel_x . . . . . . . . . . . . . . . . . . . . 42
4.7.4. sample_difference . . . . . . . . . . . . . . . . . . 42
4.8. Slice Footer . . . . . . . . . . . . . . . . . . . . . . 42
4.8.1. slice_size . . . . . . . . . . . . . . . . . . . . . 42
4.8.2. error_status . . . . . . . . . . . . . . . . . . . . 43
4.8.3. slice_crc_parity . . . . . . . . . . . . . . . . . . 43
4.9. Quantization Table Set . . . . . . . . . . . . . . . . . 43
4.9.1. quant_tables . . . . . . . . . . . . . . . . . . . . 44
4.9.2. context_count . . . . . . . . . . . . . . . . . . . . 44
5. Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 45
6. Security Considerations . . . . . . . . . . . . . . . . . . . 45
7. Media Type Definition . . . . . . . . . . . . . . . . . . . . 46
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
9. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 48
10. Normative References . . . . . . . . . . . . . . . . . . . . 48
11. Informative References . . . . . . . . . . . . . . . . . . . 49
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Appendix A. Multi-theaded decoder implementation suggestions . . 50
Appendix B. Future handling of some streams created by non
conforming encoders . . . . . . . . . . . . . . . . . . . 50
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
1. Introduction
This document describes FFV1, a lossless video encoding format. The
design of FFV1 considers the storage of image characteristics, data
fixity, and the optimized use of encoding time and storage
requirements. FFV1 is designed to support a wide range of lossless
video applications such as long-term audiovisual preservation,
scientific imaging, screen recording, and other video encoding
scenarios that seek to avoid the generational loss of lossy video
encodings.
This document defines version 0, 1 and 3 of FFV1. The distinctions
of the versions are provided throughout the document, but in summary:
* Version 0 of FFV1 was the original implementation of FFV1 and has
been in non-experimental use since April 14, 2006 [FFV1_V0].
* Version 1 of FFV1 adds support of more video bit depths and has
been in use since April 24, 2009 [FFV1_V1].
* Version 2 of FFV1 only existed in experimental form and is not
described by this document, but is available as a LyX file at
https://github.com/FFmpeg/FFV1/
blob/8ad772b6d61c3dd8b0171979a2cd9f11924d5532/ffv1.lyx
(https://github.com/FFmpeg/FFV1/
blob/8ad772b6d61c3dd8b0171979a2cd9f11924d5532/ffv1.lyx).
* Version 3 of FFV1 adds several features such as increased
description of the characteristics of the encoding images and
embedded CRC data to support fixity verification of the encoding.
Version 3 has been in non-experimental use since August 17, 2013
[FFV1_V3].
This document assumes familiarity with mathematical and coding
concepts such as Range coding [range-coding] and YCbCr color spaces
[YCbCr].
This specification describes the valid bitstream and how to decode
such valid bitstream. Bitstreams not conforming to this
specification or how they are handled is outside this specification.
A decoder could reject every invalid bitstream or attempt to perform
error concealment or re-download or use a redundant copy of the
invalid part or any other action it deems appropriate.
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2. Notation and Conventions
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.1. Definitions
"Container": Format that encapsulates "Frames" (see Section 4.3) and
(when required) a "Configuration Record" into a bitstream.
"Sample": The smallest addressable representation of a color
component or a luma component in a "Frame". Examples of "Sample" are
Luma, Blue Chrominance, Red Chrominance, Transparency, Red, Green,
and Blue.
"Plane": A discrete component of a static image comprised of
"Samples" that represent a specific quantification of "Samples" of
that image.
"Pixel": The smallest addressable representation of a color in a
"Frame". It is composed of one or more "Samples".
"ESC": An ESCape symbol to indicate that the symbol to be stored is
too large for normal storage and that an alternate storage method is
used.
"MSB": Most Significant Bit, the bit that can cause the largest
change in magnitude of the symbol.
"VLC": Variable Length Code, a code that maps source symbols to a
variable number of bits.
"RGB": A reference to the method of storing the value of a "Pixel" by
using three numeric values that represent Red, Green, and Blue.
"YCbCr": A reference to the method of storing the value of a "Pixel"
by using three numeric values that represent the luma of the "Pixel"
(Y) and the chrominance of the "Pixel" (Cb and Cr). YCbCr word is
used for historical reasons and currently references any color space
relying on 1 luma "Sample" and 2 chrominance "Samples", e.g. YCbCr,
YCgCo or ICtCp. The exact meaning of the three numeric values is
unspecified.
2.2. Conventions
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2.2.1. Pseudo-code
The FFV1 bitstream is described in this document using pseudo-code.
Note that the pseudo-code is used for clarity in order to illustrate
the structure of FFV1 and not intended to specify any particular
implementation. The pseudo-code used is based upon the C programming
language [ISO.9899.1990] and uses its "if/else", "while" and "for"
keywords as well as functions defined within this document.
2.2.2. Arithmetic Operators
Note: the operators and the order of precedence are the same as used
in the C programming language [ISO.9899.2018], with the exception of
">>" (removal of implementation defined behavior) and "^" (power
instead of XOR) operators which are re-defined within this section.
"a + b" means a plus b.
"a - b" means a minus b.
"-a" means negation of a.
"a * b" means a multiplied by b.
"a / b" means a divided by b.
"a ^ b" means a raised to the b-th power.
"a & b" means bit-wise "and" of a and b.
"a | b" means bit-wise "or" of a and b.
"a >> b" means arithmetic right shift of two's complement integer
representation of a by b binary digits. This is equivalent to
dividing a by 2, b times, with rounding toward negative infinity.
"a << b" means arithmetic left shift of two's complement integer
representation of a by b binary digits.
2.2.3. Assignment Operators
"a = b" means a is assigned b.
"a++" is equivalent to a is assigned a + 1.
"a--" is equivalent to a is assigned a - 1.
"a += b" is equivalent to a is assigned a + b.
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"a -= b" is equivalent to a is assigned a - b.
"a *= b" is equivalent to a is assigned a * b.
2.2.4. Comparison Operators
"a > b" means a is greater than b.
"a >= b" means a is greater than or equal to b.
"a < b" means a is less than b.
"a <= b" means a is less than or equal b.
"a == b" means a is equal to b.
"a != b" means a is not equal to b.
"a && b" means Boolean logical "and" of a and b.
"a || b" means Boolean logical "or" of a and b.
"!a" means Boolean logical "not" of a.
"a ? b : c" if a is true, then b, otherwise c.
2.2.5. Mathematical Functions
"floor(a)" means the largest integer less than or equal to a.
"ceil(a)" means the smallest integer greater than or equal to a.
"sign(a)" extracts the sign of a number, i.e. if a < 0 then -1, else
if a > 0 then 1, else 0.
"abs(a)" means the absolute value of a, i.e. "abs(a)" = "sign(a) *
a".
"log2(a)" means the base-two logarithm of a.
"min(a,b)" means the smallest of two values a and b.
"max(a,b)" means the largest of two values a and b.
"median(a,b,c)" means the numerical middle value in a data set of a,
b, and c, i.e. a+b+c-min(a,b,c)-max(a,b,c).
"A <== B" means B implies A.
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"A <==> B" means A <== B , B <== A.
2.2.6. Order of Operation Precedence
When order of precedence is not indicated explicitly by use of
parentheses, operations are evaluated in the following order (from
top to bottom, operations of same precedence being evaluated from
left to right). This order of operations is based on the order of
operations used in Standard C.
a++, a--
!a, -a
a ^ b
a * b, a / b, a % b
a + b, a - b
a << b, a >> b
a < b, a <= b, a > b, a >= b
a == b, a != b
a & b
a | b
a && b
a || b
a ? b : c
a = b, a += b, a -= b, a *= b
2.2.7. Range
"a...b" means any value starting from a to b, inclusive.
2.2.8. NumBytes
"NumBytes" is a non-negative integer that expresses the size in 8-bit
octets of a particular FFV1 "Configuration Record" or "Frame". FFV1
relies on its "Container" to store the "NumBytes" values; see
Section 4.2.3.
2.2.9. Bitstream Functions
2.2.9.1. remaining_bits_in_bitstream
"remaining_bits_in_bitstream( )" means the count of remaining bits
after the pointer in that "Configuration Record" or "Frame". It is
computed from the "NumBytes" value multiplied by 8 minus the count of
bits of that "Configuration Record" or "Frame" already read by the
bitstream parser.
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2.2.9.2. remaining_symbols_in_syntax
"remaining_symbols_in_syntax( )" is true as long as the RangeCoder
has not consumed all the given input bytes.
2.2.9.3. byte_aligned
"byte_aligned( )" is true if "remaining_bits_in_bitstream( NumBytes
)" is a multiple of 8, otherwise false.
2.2.9.4. get_bits
"get_bits( i )" is the action to read the next "i" bits in the
bitstream, from most significant bit to least significant bit, and to
return the corresponding value. The pointer is increased by "i".
3. Sample Coding
For each "Slice" (as described in Section 4.4) of a "Frame", the
"Planes", "Lines", and "Samples" are coded in an order determined by
the "Color Space" (see Section 3.7). Each "Sample" is predicted by
the median predictor as described in Section 3.3 from other "Samples"
within the same "Plane" and the difference is stored using the method
described in Section 3.8.
3.1. Border
A border is assumed for each coded "Slice" for the purpose of the
median predictor and context according to the following rules:
* one column of "Samples" to the left of the coded slice is assumed
as identical to the "Samples" of the leftmost column of the coded
slice shifted down by one row. The value of the topmost "Sample"
of the column of "Samples" to the left of the coded slice is
assumed to be "0"
* one column of "Samples" to the right of the coded slice is assumed
as identical to the "Samples" of the rightmost column of the coded
slice
* an additional column of "Samples" to the left of the coded slice
and two rows of "Samples" above the coded slice are assumed to be
"0"
Figure 1 depicts a slice of 9 "Samples" "a,b,c,d,e,f,g,h,i" in a 3x3
arrangement along with its assumed border.
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+---+---+---+---+---+---+---+---+
| 0 | 0 | | 0 | 0 | 0 | | 0 |
+---+---+---+---+---+---+---+---+
| 0 | 0 | | 0 | 0 | 0 | | 0 |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| 0 | 0 | | a | b | c | | c |
+---+---+---+---+---+---+---+---+
| 0 | a | | d | e | f | | f |
+---+---+---+---+---+---+---+---+
| 0 | d | | g | h | i | | i |
+---+---+---+---+---+---+---+---+
Figure 1: A depiction of FFV1's assumed border for a set example
Samples.
3.2. Samples
Relative to any "Sample" "X", six other relatively positioned
"Samples" from the coded "Samples" and presumed border are identified
according to the labels used in Figure 2. The labels for these
relatively positioned "Samples" are used within the median predictor
and context.
+---+---+---+---+
| | | T | |
+---+---+---+---+
| |tl | t |tr |
+---+---+---+---+
| L | l | X | |
+---+---+---+---+
Figure 2: A depiction of how relatively positions Samples are
references within this document.
The labels for these relative "Samples" are made of the first letters
of the words Top, Left and Right.
3.3. Median Predictor
The prediction for any "Sample" value at position "X" may be computed
based upon the relative neighboring values of "l", "t", and "tl" via
this equation:
median(l, t, l + t - tl)
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Note, this prediction template is also used in [ISO.14495-1.1999] and
[HuffYUV].
Exception for the median predictor: if "colorspace_type == 0 &&
bits_per_raw_sample == 16 && ( coder_type == 1 || coder_type == 2 )",
the following median predictor MUST be used:
median(left16s, top16s, left16s + top16s - diag16s)
where:
left16s = l >= 32768 ? ( l - 65536 ) : l top16s = t >= 32768 ? ( t -
65536 ) : t diag16s = tl >= 32768 ? ( tl - 65536 ) : tl
Background: a two's complement signed 16-bit signed integer was used
for storing "Sample" values in all known implementations of FFV1
bitstream. So in some circumstances, the most significant bit was
wrongly interpreted (used as a sign bit instead of the 16th bit of an
unsigned integer). Note that when the issue was discovered, the only
configuration of all known implementations being impacted is 16-bit
YCbCr with no Pixel transformation with Range Coder coder, as other
potentially impacted configurations (e.g. 15/16-bit JPEG2000-RCT with
Range Coder coder, or 16-bit content with Golomb Rice coder) were
implemented nowhere [ISO.15444-1.2016]. In the meanwhile, 16-bit
JPEG2000-RCT with Range Coder coder was implemented without this
issue in one implementation and validated by one conformance checker.
It is expected (to be confirmed) to remove this exception for the
median predictor in the next version of the FFV1 bitstream.
3.4. Context
Relative to any "Sample" "X", the Quantized Sample Differences "L-l",
"l-tl", "tl-t", "T-t", and "t-tr" are used as context:
context = Q_{0}[l - tl] +
Q_{1}[tl - t] +
Q_{2}[t - tr] +
Q_{3}[L - l] +
Q_{4}[T - t]
Figure 3
If "context >= 0" then "context" is used and the difference between
the "Sample" and its predicted value is encoded as is, else
"-context" is used and the difference between the "Sample" and its
predicted value is encoded with a flipped sign.
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3.5. Quantization Table Sets
The FFV1 bitstream contains one or more Quantization Table Sets.
Each Quantization Table Set contains exactly 5 Quantization Tables
with each Quantization Table corresponding to one of the five
Quantized Sample Differences. For each Quantization Table, both the
number of quantization steps and their distribution are stored in the
FFV1 bitstream; each Quantization Table has exactly 256 entries, and
the 8 least significant bits of the Quantized Sample Difference are
used as index:
Q_{j}[k] = quant_tables[i][j][k&255]
Figure 4
In this formula, "i" is the Quantization Table Set index, "j" is the
Quantized Table index, "k" the Quantized Sample Difference.
3.6. Quantization Table Set Indexes
For each "Plane" of each slice, a Quantization Table Set is selected
from an index:
* For Y "Plane", "quant_table_set_index[ 0 ]" index is used
* For Cb and Cr "Planes", "quant_table_set_index[ 1 ]" index is used
* For extra "Plane", "quant_table_set_index[ (version <= 3 ||
chroma_planes) ? 2 : 1 ]" index is used
Background: in first implementations of FFV1 bitstream, the index for
Cb and Cr "Planes" was stored even if it is not used (chroma_planes
set to 0), this index is kept for "version" <= 3 in order to keep
compatibility with FFV1 bitstreams in the wild.
3.7. Color spaces
FFV1 supports several color spaces. The count of allowed coded
planes and the meaning of the extra "Plane" are determined by the
selected color space.
The FFV1 bitstream interleaves data in an order determined by the
color space. In YCbCr for each "Plane", each "Line" is coded from
top to bottom and for each "Line", each "Sample" is coded from left
to right. In JPEG2000-RCT for each "Line" from top to bottom, each
"Plane" is coded and for each "Plane", each "Sample" is encoded from
left to right.
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3.7.1. YCbCr
This color space allows 1 to 4 "Planes".
The Cb and Cr "Planes" are optional, but if used then MUST be used
together. Omitting the Cb and Cr "Planes" codes the frames in
grayscale without color data.
An optional transparency "Plane" can be used to code transparency
data.
An FFV1 "Frame" using YCbCr MUST use one of the following
arrangements:
* Y
* Y, Transparency
* Y, Cb, Cr
* Y, Cb, Cr, Transparency
The Y "Plane" MUST be coded first. If the Cb and Cr "Planes" are
used then they MUST be coded after the Y "Plane". If a transparency
"Plane" is used, then it MUST be coded last.
3.7.2. RGB
This color space allows 3 or 4 "Planes".
An optional transparency "Plane" can be used to code transparency
data.
JPEG2000-RCT is a Reversible Color Transform that codes RGB (red,
green, blue) "Planes" losslessly in a modified YCbCr color space
[ISO.15444-1.2016]. Reversible Pixel transformations between YCbCr
and RGB use the following formulae.
Cb = b - g
Cr = r - g
Y = g + (Cb + Cr) >> 2
g = Y - (Cb + Cr) >> 2
r = Cr + g
b = Cb + g
Figure 5
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Exception for the JPEG2000-RCT conversion: if "bits_per_raw_sample"
is between 9 and 15 inclusive and "extra_plane" is 0, the following
formulae for reversible conversions between YCbCr and RGB MUST be
used instead of the ones above:
Cb = g - b
Cr = r - b
Y = b +(Cb + Cr) >> 2
b = Y -(Cb + Cr) >> 2
r = Cr + b
g = Cb + b
Figure 6
Background: At the time of this writing, in all known implementations
of FFV1 bitstream, when "bits_per_raw_sample" was between 9 and 15
inclusive and "extra_plane" is 0, GBR "Planes" were used as BGR
"Planes" during both encoding and decoding. In the meanwhile, 16-bit
JPEG2000-RCT was implemented without this issue in one implementation
and validated by one conformance checker. Methods to address this
exception for the transform are under consideration for the next
version of the FFV1 bitstream.
Cb and Cr are positively offset by "1 << bits_per_raw_sample" after
the conversion from RGB to the modified YCbCr and are negatively
offseted by the same value before the conversion from the modified
YCbCr to RGB, in order to have only non-negative values after the
conversion.
When FFV1 uses the JPEG2000-RCT, the horizontal "Lines" are
interleaved to improve caching efficiency since it is most likely
that the JPEG2000-RCT will immediately be converted to RGB during
decoding. The interleaved coding order is also Y, then Cb, then Cr,
and then if used transparency.
As an example, a "Frame" that is two "Pixels" wide and two "Pixels"
high, could comprise the following structure:
+------------------------+------------------------+
| Pixel(1,1) | Pixel(2,1) |
| Y(1,1) Cb(1,1) Cr(1,1) | Y(2,1) Cb(2,1) Cr(2,1) |
+------------------------+------------------------+
| Pixel(1,2) | Pixel(2,2) |
| Y(1,2) Cb(1,2) Cr(1,2) | Y(2,2) Cb(2,2) Cr(2,2) |
+------------------------+------------------------+
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In JPEG2000-RCT, the coding order would be left to right and then top
to bottom, with values interleaved by "Lines" and stored in this
order:
Y(1,1) Y(2,1) Cb(1,1) Cb(2,1) Cr(1,1) Cr(2,1) Y(1,2) Y(2,2) Cb(1,2)
Cb(2,2) Cr(1,2) Cr(2,2)
3.8. Coding of the Sample Difference
Instead of coding the n+1 bits of the Sample Difference with Huffman
or Range coding (or n+2 bits, in the case of JPEG2000-RCT), only the
n (or n+1, in the case of JPEG2000-RCT) least significant bits are
used, since this is sufficient to recover the original "Sample". In
the equation below, the term "bits" represents "bits_per_raw_sample +
1" for JPEG2000-RCT or "bits_per_raw_sample" otherwise:
coder_input =
[(sample_difference + 2 ^ (bits-1)) & (2 ^ bits - 1)] - 2 ^ (bits - 1)
Figure 7
3.8.1. Range Coding Mode
Early experimental versions of FFV1 used the CABAC Arithmetic coder
from H.264 as defined in [ISO.14496-10.2014] but due to the uncertain
patent/royalty situation, as well as its slightly worse performance,
CABAC was replaced by a Range coder based on an algorithm defined by
G. Nigel and N. Martin in 1979 [range-coding].
3.8.1.1. Range Binary Values
To encode binary digits efficiently a Range coder is used. "C(i)" is
the i-th Context. "B(i)" is the i-th byte of the bytestream. "b(i)"
is the i-th Range coded binary value, "S(0,i)" is the i-th initial
state. The length of the bytestream encoding n binary symbols is
"j(n)" bytes.
r_{i} = floor( ( R_{i} * S_{i,C_{i}} ) / 2 ^ 8 )
Figure 8
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S_{i+1,C_{i}} = zero_state_{S_{i,C_{i}}} AND
l_i = L_i AND
t_i = R_i - r_i <==
b_i = 0 <==>
L_i < R_i - r_i
S_{i+1,C_{i}} = one_state_{S_{i,C_{i}}} AND
l_i = L_i - R_i + r_i AND
t_i = r_i <==
b_i = 1 <==>
L_i >= R_i - r_i
Figure 9
S_{i+1,k} = S_{i,k} <== C_i != k
Figure 10
R_{i+1} = 2 ^ 8 * t_{i} AND
L_{i+1} = 2 ^ 8 * l_{i} + B_{j_{i}} AND
j_{i+1} = j_{i} + 1 <==
t_{i} < 2 ^ 8
R_{i+1} = t_{i} AND
L_{i+1} = l_{i} AND
j_{i+1} = j_{i} <==
t_{i} >= 2 ^ 8
Figure 11
R_{0} = 65280
Figure 12
L_{0} = 2 ^ 8 * B_{0} + B_{1}
Figure 13
j_{0} = 2
Figure 14
3.8.1.1.1. Termination
The range coder can be used in three modes.
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* In "Open mode" when decoding, every symbol the reader attempts to
read is available. In this mode arbitrary data can have been
appended without affecting the range coder output. This mode is
not used in FFV1.
* In "Closed mode" the length in bytes of the bytestream is provided
to the range decoder. Bytes beyond the length are read as 0 by
the range decoder. This is generally one byte shorter than the
open mode.
* In "Sentinel mode" the exact length in bytes is not known and thus
the range decoder MAY read into the data that follows the range
coded bytestream by one byte. In "Sentinel mode", the end of the
range coded bytestream is a binary symbol with state 129, which
value SHALL be discarded. After reading this symbol, the range
decoder will have read one byte beyond the end of the range coded
bytestream. This way the byte position of the end can be
determined. Bytestreams written in "Sentinel mode" can be read in
"Closed mode" if the length can be determined, in this case the
last (sentinel) symbol will be read non-corrupted and be of value
0.
Above describes the range decoding. Encoding is defined as any
process which produces a decodable bytestream.
There are three places where range coder termination is needed in
FFV1. First is in the "Configuration Record", in this case the size
of the range coded bytestream is known and handled as "Closed mode".
Second is the switch from the "Slice Header" which is range coded to
Golomb coded slices as "Sentinel mode". Third is the end of range
coded Slices which need to terminate before the CRC at their end.
This can be handled as "Sentinel mode" or as "Closed mode" if the CRC
position has been determined.
3.8.1.2. Range Non Binary Values
To encode scalar integers, it would be possible to encode each bit
separately and use the past bits as context. However that would mean
255 contexts per 8-bit symbol that is not only a waste of memory but
also requires more past data to reach a reasonably good estimate of
the probabilities. Alternatively assuming a Laplacian distribution
and only dealing with its variance and mean (as in Huffman coding)
would also be possible, however, for maximum flexibility and
simplicity, the chosen method uses a single symbol to encode if a
number is 0, and if not, encodes the number using its exponent,
mantissa and sign. The exact contexts used are best described by
Figure 15, followed by some comments.
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pseudo-code | type
--------------------------------------------------------------|-----
void put_symbol(RangeCoder *c, uint8_t *state, int v, int \ |
is_signed) { |
int i; |
put_rac(c, state+0, !v); |
if (v) { |
int a= abs(v); |
int e= log2(a); |
|
for (i = 0; i < e; i++) { |
put_rac(c, state+1+min(i,9), 1); //1..10 |
} |
|
put_rac(c, state+1+min(i,9), 0); |
for (i = e-1; i >= 0; i--) { |
put_rac(c, state+22+min(i,9), (a>>i)&1); //22..31 |
} |
|
if (is_signed) { |
put_rac(c, state+11 + min(e, 10), v < 0); //11..21|
} |
} |
} |
Figure 15: A pseudo-code description of the contexts of Range Non
Binary Values.
3.8.1.3. Initial Values for the Context Model
At keyframes all Range coder state variables are set to their initial
state.
3.8.1.4. State Transition Table
one_state_{i} =
default_state_transition_{i} + state_transition_delta_{i}
Figure 16
zero_state_{i} = 256 - one_state_{256-i}
Figure 17
3.8.1.5. default_state_transition
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0, 0, 0, 0, 0, 0, 0, 0, 20, 21, 22, 23, 24, 25, 26, 27,
28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42,
43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 56, 57,
58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73,
74, 75, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88,
89, 90, 91, 92, 93, 94, 94, 95, 96, 97, 98, 99,100,101,102,103,
104,105,106,107,108,109,110,111,112,113,114,114,115,116,117,118,
119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,133,
134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,
150,151,152,152,153,154,155,156,157,158,159,160,161,162,163,164,
165,166,167,168,169,170,171,171,172,173,174,175,176,177,178,179,
180,181,182,183,184,185,186,187,188,189,190,190,191,192,194,194,
195,196,197,198,199,200,201,202,202,204,205,206,207,208,209,209,
210,211,212,213,215,215,216,217,218,219,220,220,222,223,224,225,
226,227,227,229,229,230,231,232,234,234,235,236,237,238,239,240,
241,242,243,244,245,246,247,248,248, 0, 0, 0, 0, 0, 0, 0,
3.8.1.6. Alternative State Transition Table
The alternative state transition table has been built using iterative
minimization of frame sizes and generally performs better than the
default. To use it, the "coder_type" (see Section 4.1.3) MUST be set
to 2 and the difference to the default MUST be stored in the
"Parameters", see Section 4.1. The reference implementation of FFV1
in FFmpeg uses Figure 18 by default at the time of this writing when
Range coding is used.
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0, 10, 10, 10, 10, 16, 16, 16, 28, 16, 16, 29, 42, 49, 20, 49,
59, 25, 26, 26, 27, 31, 33, 33, 33, 34, 34, 37, 67, 38, 39, 39,
40, 40, 41, 79, 43, 44, 45, 45, 48, 48, 64, 50, 51, 52, 88, 52,
53, 74, 55, 57, 58, 58, 74, 60,101, 61, 62, 84, 66, 66, 68, 69,
87, 82, 71, 97, 73, 73, 82, 75,111, 77, 94, 78, 87, 81, 83, 97,
85, 83, 94, 86, 99, 89, 90, 99,111, 92, 93,134, 95, 98,105, 98,
105,110,102,108,102,118,103,106,106,113,109,112,114,112,116,125,
115,116,117,117,126,119,125,121,121,123,145,124,126,131,127,129,
165,130,132,138,133,135,145,136,137,139,146,141,143,142,144,148,
147,155,151,149,151,150,152,157,153,154,156,168,158,162,161,160,
172,163,169,164,166,184,167,170,177,174,171,173,182,176,180,178,
175,189,179,181,186,183,192,185,200,187,191,188,190,197,193,196,
197,194,195,196,198,202,199,201,210,203,207,204,205,206,208,214,
209,211,221,212,213,215,224,216,217,218,219,220,222,228,223,225,
226,224,227,229,240,230,231,232,233,234,235,236,238,239,237,242,
241,243,242,244,245,246,247,248,249,250,251,252,252,253,254,255,
Figure 18: Alternative state transition table for Range coding.
3.8.2. Golomb Rice Mode
The end of the bitstream of the "Frame" is filled with 0-bits until
that the bitstream contains a multiple of 8 bits.
3.8.2.1. Signed Golomb Rice Codes
This coding mode uses Golomb Rice codes. The VLC is split into two
parts. The prefix stores the most significant bits and the suffix
stores the k least significant bits or stores the whole number in the
ESC case.
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pseudo-code | type
--------------------------------------------------------------|-----
int get_ur_golomb(k) { |
for (prefix = 0; prefix < 12; prefix++) { |
if (get_bits(1)) { |
return get_bits(k) + (prefix << k) |
} |
} |
return get_bits(bits) + 11 |
} |
|
int get_sr_golomb(k) { |
v = get_ur_golomb(k); |
if (v & 1) return - (v >> 1) - 1; |
else return (v >> 1); |
}
3.8.2.1.1. Prefix
+----------------+-------+
| bits | value |
+================+=======+
| 1 | 0 |
+----------------+-------+
| 01 | 1 |
+----------------+-------+
| ... | ... |
+----------------+-------+
| 0000 0000 01 | 9 |
+----------------+-------+
| 0000 0000 001 | 10 |
+----------------+-------+
| 0000 0000 0001 | 11 |
+----------------+-------+
| 0000 0000 0000 | ESC |
+----------------+-------+
Table 1
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3.8.2.1.2. Suffix
+---------+----------------------------------------+
+=========+========================================+
| non ESC | the k least significant bits MSB first |
+---------+----------------------------------------+
| ESC | the value - 11, in MSB first order |
+---------+----------------------------------------+
Table 2
"ESC" MUST NOT be used if the value can be coded as "non ESC".
3.8.2.1.3. Examples
+-----+-------------------------+-------+
| k | bits | value |
+=====+=========================+=======+
| 0 | "1" | 0 |
+-----+-------------------------+-------+
| 0 | "001" | 2 |
+-----+-------------------------+-------+
| 2 | "1 00" | 0 |
+-----+-------------------------+-------+
| 2 | "1 10" | 2 |
+-----+-------------------------+-------+
| 2 | "01 01" | 5 |
+-----+-------------------------+-------+
| any | "000000000000 10000000" | 139 |
+-----+-------------------------+-------+
Table 3
3.8.2.2. Run Mode
Run mode is entered when the context is 0 and left as soon as a non-0
difference is found. The level is identical to the predicted one.
The run and the first different level are coded.
3.8.2.2.1. Run Length Coding
The run value is encoded in two parts. The prefix part stores the
more significant part of the run as well as adjusting the "run_index"
that determines the number of bits in the less significant part of
the run. The second part of the value stores the less significant
part of the run as it is. The run_index is reset for each "Plane"
and slice to 0.
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pseudo-code | type
--------------------------------------------------------------|-----
log2_run[41]={ |
0, 0, 0, 0, 1, 1, 1, 1, |
2, 2, 2, 2, 3, 3, 3, 3, |
4, 4, 5, 5, 6, 6, 7, 7, |
8, 9,10,11,12,13,14,15, |
16,17,18,19,20,21,22,23, |
24, |
}; |
|
if (run_count == 0 && run_mode == 1) { |
if (get_bits(1)) { |
run_count = 1 << log2_run[run_index]; |
if (x + run_count <= w) { |
run_index++; |
} |
} else { |
if (log2_run[run_index]) { |
run_count = get_bits(log2_run[run_index]); |
} else { |
run_count = 0; |
} |
if (run_index) { |
run_index--; |
} |
run_mode = 2; |
} |
} |
The "log2_run" array is also used within [ISO.14495-1.1999].
3.8.2.3. Scalar Mode
Each difference is coded with the per context mean prediction removed
and a per context value for k.
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get_vlc_symbol(state) {
i = state->count;
k = 0;
while (i < state->error_sum) {
k++;
i += i;
}
v = get_sr_golomb(k);
if (2 * state->drift < -state->count) {
v = -1 - v;
}
ret = sign_extend(v + state->bias, bits);
state->error_sum += abs(v);
state->drift += v;
if (state->count == 128) {
state->count >>= 1;
state->drift >>= 1;
state->error_sum >>= 1;
}
state->count++;
if (state->drift <= -state->count) {
state->bias = max(state->bias - 1, -128);
state->drift = max(state->drift + state->count,
-state->count + 1);
} else if (state->drift > 0) {
state->bias = min(state->bias + 1, 127);
state->drift = min(state->drift - state->count, 0);
}
return ret;
}
3.8.2.3.1. Level Coding
Level coding is identical to the normal difference coding with the
exception that the 0 value is removed as it cannot occur:
diff = get_vlc_symbol(context_state);
if (diff >= 0) {
diff++;
}
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Note, this is different from JPEG-LS, which doesn't use prediction in
run mode and uses a different encoding and context model for the last
difference. On a small set of test "Samples" the use of prediction
slightly improved the compression rate.
3.8.2.4. Initial Values for the VLC context state
At keyframes all coder state variables are set to their initial
state.
drift = 0;
error_sum = 4;
bias = 0;
count = 1;
4. Bitstream
An FFV1 bitstream is composed of a series of one or more "Frames" and
(when required) a "Configuration Record".
Within the following sub-sections, pseudo-code is used to explain the
structure of each FFV1 bitstream component, as described in
Section 2.2.1. Table 4 lists symbols used to annotate that pseudo-
code in order to define the storage of the data referenced in that
line of pseudo-code.
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+--------+----------------------------------------------+
| Symbol | Definition |
+========+==============================================+
| u(n) | unsigned big endian integer using n bits |
+--------+----------------------------------------------+
| sg | Golomb Rice coded signed scalar symbol coded |
| | with the method described in Section 3.8.2 |
+--------+----------------------------------------------+
| br | Range coded Boolean (1-bit) symbol with the |
| | method described in Section 3.8.1.1 |
+--------+----------------------------------------------+
| ur | Range coded unsigned scalar symbol coded |
| | with the method described in Section 3.8.1.2 |
+--------+----------------------------------------------+
| sr | Range coded signed scalar symbol coded with |
| | the method described in Section 3.8.1.2 |
+--------+----------------------------------------------+
| sd | Sample difference coded with the method |
| | described in Section 3.8 |
+--------+----------------------------------------------+
Table 4: Definition of pseudo-code symbols for this
document.
The same context that is initialized to 128 is used for all fields in
the header.
The following MUST be provided by external means during
initialization of the decoder:
"frame_pixel_width" is defined as "Frame" width in "Pixels".
"frame_pixel_height" is defined as "Frame" height in "Pixels".
Default values at the decoder initialization phase:
"ConfigurationRecordIsPresent" is set to 0.
4.1. Parameters
The "Parameters" section contains significant characteristics about
the decoding configuration used for all instances of "Frame" (in FFV1
version 0 and 1) or the whole FFV1 bitstream (other versions),
including the stream version, color configuration, and quantization
tables. Figure 19 describes the contents of the bitstream.
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pseudo-code | type
--------------------------------------------------------------|-----
Parameters( ) { |
version | ur
if (version >= 3) { |
micro_version | ur
} |
coder_type | ur
if (coder_type > 1) { |
for (i = 1; i < 256; i++) { |
state_transition_delta[ i ] | sr
} |
} |
colorspace_type | ur
if (version >= 1) { |
bits_per_raw_sample | ur
} |
chroma_planes | br
log2_h_chroma_subsample | ur
log2_v_chroma_subsample | ur
extra_plane | br
if (version >= 3) { |
num_h_slices - 1 | ur
num_v_slices - 1 | ur
quant_table_set_count | ur
} |
for (i = 0; i < quant_table_set_count; i++) { |
QuantizationTableSet( i ) |
} |
if (version >= 3) { |
for (i = 0; i < quant_table_set_count; i++) { |
states_coded | br
if (states_coded) { |
for (j = 0; j < context_count[ i ]; j++) { |
for (k = 0; k < CONTEXT_SIZE; k++) { |
initial_state_delta[ i ][ j ][ k ] | sr
} |
} |
} |
} |
ec | ur
intra | ur
} |
} |
Figure 19: A pseudo-code description of the bitstream contents.
CONTEXT_SIZE is 32.
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4.1.1. version
"version" specifies the version of the FFV1 bitstream.
Each version is incompatible with other versions: decoders SHOULD
reject FFV1 bitstreams due to an unknown version.
Decoders SHOULD reject FFV1 bitstreams with version <= 1 &&
ConfigurationRecordIsPresent == 1.
Decoders SHOULD reject FFV1 bitstreams with version >= 3 &&
ConfigurationRecordIsPresent == 0.
+-------+-------------------------+
| value | version |
+=======+=========================+
| 0 | FFV1 version 0 |
+-------+-------------------------+
| 1 | FFV1 version 1 |
+-------+-------------------------+
| 2 | reserved* |
+-------+-------------------------+
| 3 | FFV1 version 3 |
+-------+-------------------------+
| Other | reserved for future use |
+-------+-------------------------+
Table 5
* Version 2 was experimental and this document does not describe it.
4.1.2. micro_version
"micro_version" specifies the micro-version of the FFV1 bitstream.
After a version is considered stable (a micro-version value is
assigned to be the first stable variant of a specific version), each
new micro-version after this first stable variant is compatible with
the previous micro-version: decoders SHOULD NOT reject FFV1
bitstreams due to an unknown micro-version equal or above the micro-
version considered as stable.
Meaning of "micro_version" for "version" 3:
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+-------+-------------------------+
| value | micro_version |
+=======+=========================+
| 0...3 | reserved* |
+-------+-------------------------+
| 4 | first stable variant |
+-------+-------------------------+
| Other | reserved for future use |
+-------+-------------------------+
Table 6: The definitions for
"micro_version" values for FFV1
version 3.
* development versions may be incompatible with the stable variants.
4.1.3. coder_type
"coder_type" specifies the coder used.
+-------+-------------------------------------------------+
| value | coder used |
+=======+=================================================+
| 0 | Golomb Rice |
+-------+-------------------------------------------------+
| 1 | Range Coder with default state transition table |
+-------+-------------------------------------------------+
| 2 | Range Coder with custom state transition table |
+-------+-------------------------------------------------+
| Other | reserved for future use |
+-------+-------------------------------------------------+
Table 7
Restrictions:
If "coder_type" is 0, then "bits_per_raw_sample" SHOULD NOT be > 8.
Background: At the time of this writing, there is no known
implementation of FFV1 bitstream supporting Golomb Rice algorithm
with "bits_per_raw_sample" greater than 8, and Range Coder is
prefered.
4.1.4. state_transition_delta
"state_transition_delta" specifies the Range coder custom state
transition table.
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If "state_transition_delta" is not present in the FFV1 bitstream, all
Range coder custom state transition table elements are assumed to be
0.
4.1.5. colorspace_type
"colorspace_type" specifies the color space encoded, the pixel
transformation used by the encoder, the extra plane content, as well
as interleave method.
+-------+-------------+----------------+--------------+-------------+
| value | color space | pixel | extra plane | interleave |
| | encoded | transformation | content | method |
+=======+=============+================+==============+=============+
| 0 | YCbCr | None | Transparency | "Plane" |
| | | | | then |
| | | | | "Line" |
+-------+-------------+----------------+--------------+-------------+
| 1 | RGB | JPEG2000-RCT | Transparency | "Line" |
| | | | | then |
| | | | | "Plane" |
+-------+-------------+----------------+--------------+-------------+
| Other | reserved | reserved for | reserved for | reserved |
| | for future | future use | future use | for future |
| | use | | | use |
+-------+-------------+----------------+--------------+-------------+
Table 8
FFV1 bitstreams with "colorspace_type" == 1 && ("chroma_planes" !=
1 || "log2_h_chroma_subsample" != 0 || "log2_v_chroma_subsample" !=
0) are not part of this specification.
4.1.6. chroma_planes
"chroma_planes" indicates if chroma (color) "Planes" are present.
+-------+---------------------------------+
| value | presence |
+=======+=================================+
| 0 | chroma "Planes" are not present |
+-------+---------------------------------+
| 1 | chroma "Planes" are present |
+-------+---------------------------------+
Table 9
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4.1.7. bits_per_raw_sample
"bits_per_raw_sample" indicates the number of bits for each "Sample".
Inferred to be 8 if not present.
+-------+-----------------------------------+
| value | bits for each sample |
+=======+===================================+
| 0 | reserved* |
+-------+-----------------------------------+
| Other | the actual bits for each "Sample" |
+-------+-----------------------------------+
Table 10
* Encoders MUST NOT store "bits_per_raw_sample" = 0. Decoders SHOULD
accept and interpret "bits_per_raw_sample" = 0 as 8.
4.1.8. log2_h_chroma_subsample
"log2_h_chroma_subsample" indicates the subsample factor, stored in
powers to which the number 2 must be raised, between luma and chroma
width ("chroma_width = 2 ^ -log2_h_chroma_subsample * luma_width").
4.1.9. log2_v_chroma_subsample
"log2_v_chroma_subsample" indicates the subsample factor, stored in
powers to which the number 2 must be raised, between luma and chroma
height ("chroma_height = 2 ^ -log2_v_chroma_subsample *
luma_height").
4.1.10. extra_plane
"extra_plane" indicates if an extra "Plane" is present.
+-------+------------------------------+
| value | presence |
+=======+==============================+
| 0 | extra "Plane" is not present |
+-------+------------------------------+
| 1 | extra "Plane" is present |
+-------+------------------------------+
Table 11
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4.1.11. num_h_slices
"num_h_slices" indicates the number of horizontal elements of the
slice raster.
Inferred to be 1 if not present.
4.1.12. num_v_slices
"num_v_slices" indicates the number of vertical elements of the slice
raster.
Inferred to be 1 if not present.
4.1.13. quant_table_set_count
"quant_table_set_count" indicates the number of Quantization
Table Sets. "quant_table_set_count" MUST be less than or equal to 8.
Inferred to be 1 if not present.
MUST NOT be 0.
4.1.14. states_coded
"states_coded" indicates if the respective Quantization Table Set has
the initial states coded.
Inferred to be 0 if not present.
+-------+--------------------------------+
| value | initial states |
+=======+================================+
| 0 | initial states are not present |
| | and are assumed to be all 128 |
+-------+--------------------------------+
| 1 | initial states are present |
+-------+--------------------------------+
Table 12
4.1.15. initial_state_delta
"initial_state_delta[ i ][ j ][ k ]" indicates the initial Range
coder state, it is encoded using "k" as context index and
pred = j ? initial_states[ i ][j - 1][ k ] : 128
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Figure 20
initial_state[ i ][ j ][ k ] =
( pred + initial_state_delta[ i ][ j ][ k ] ) & 255
Figure 21
4.1.16. ec
"ec" indicates the error detection/correction type.
+-------+--------------------------------------------+
| value | error detection/correction type |
+=======+============================================+
| 0 | 32-bit CRC on the global header |
+-------+--------------------------------------------+
| 1 | 32-bit CRC per slice and the global header |
+-------+--------------------------------------------+
| Other | reserved for future use |
+-------+--------------------------------------------+
Table 13
4.1.17. intra
"intra" indicates the constraint on "keyframe" in each instance of
"Frame".
Inferred to be 0 if not present.
+-------+-------------------------------------------------------+
| value | relationship |
+=======+=======================================================+
| 0 | "keyframe" can be 0 or 1 (non keyframes or keyframes) |
+-------+-------------------------------------------------------+
| 1 | "keyframe" MUST be 1 (keyframes only) |
+-------+-------------------------------------------------------+
| Other | reserved for future use |
+-------+-------------------------------------------------------+
Table 14
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4.2. Configuration Record
In the case of a FFV1 bitstream with "version >= 3", a "Configuration
Record" is stored in the underlying "Container", at the track header
level. It contains the "Parameters" used for all instances of
"Frame". The size of the "Configuration Record", "NumBytes", is
supplied by the underlying "Container".
pseudo-code | type
-----------------------------------------------------------|-----
ConfigurationRecord( NumBytes ) { |
ConfigurationRecordIsPresent = 1 |
Parameters( ) |
while (remaining_symbols_in_syntax(NumBytes - 4)) { |
reserved_for_future_use | br/ur/sr
} |
configuration_record_crc_parity | u(32)
} |
4.2.1. reserved_for_future_use
"reserved_for_future_use" has semantics that are reserved for future
use.
Encoders conforming to this version of this specification SHALL NOT
write this value.
Decoders conforming to this version of this specification SHALL
ignore its value.
4.2.2. configuration_record_crc_parity
"configuration_record_crc_parity" 32 bits that are chosen so that the
"Configuration Record" as a whole has a CRC remainder of 0.
This is equivalent to storing the CRC remainder in the 32-bit parity.
The CRC generator polynomial used is described in Section 4.8.3.
4.2.3. Mapping FFV1 into Containers
This "Configuration Record" can be placed in any file format
supporting "Configuration Records", fitting as much as possible with
how the file format uses to store "Configuration Records". The
"Configuration Record" storage place and "NumBytes" are currently
defined and supported by this version of this specification for the
following formats:
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4.2.3.1. AVI File Format
The "Configuration Record" extends the stream format chunk ("AVI ",
"hdlr", "strl", "strf") with the ConfigurationRecord bitstream.
See [AVI] for more information about chunks.
"NumBytes" is defined as the size, in bytes, of the strf chunk
indicated in the chunk header minus the size of the stream format
structure.
4.2.3.2. ISO Base Media File Format
The "Configuration Record" extends the sample description box
("moov", "trak", "mdia", "minf", "stbl", "stsd") with a "glbl" box
that contains the ConfigurationRecord bitstream. See
[ISO.14496-12.2015] for more information about boxes.
"NumBytes" is defined as the size, in bytes, of the "glbl" box
indicated in the box header minus the size of the box header.
4.2.3.3. NUT File Format
The "codec_specific_data" element (in "stream_header" packet)
contains the ConfigurationRecord bitstream. See [NUT] for more
information about elements.
"NumBytes" is defined as the size, in bytes, of the
"codec_specific_data" element as indicated in the "length" field of
"codec_specific_data".
4.2.3.4. Matroska File Format
FFV1 SHOULD use "V_FFV1" as the Matroska "Codec ID". For FFV1
versions 2 or less, the Matroska "CodecPrivate" Element SHOULD NOT be
used. For FFV1 versions 3 or greater, the Matroska "CodecPrivate"
Element MUST contain the FFV1 "Configuration Record" structure and no
other data. See [Matroska] for more information about elements.
"NumBytes" is defined as the "Element Data Size" of the
"CodecPrivate" Element.
4.3. Frame
A "Frame" is an encoded representation of a complete static image.
The whole "Frame" is provided by the underlaying container.
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A "Frame" consists of the "keyframe" field, "Parameters" (if
"version" <= 1), and a sequence of independent slices. The pseudo-
code below describes the contents of a "Frame".
pseudo-code | type
--------------------------------------------------------------|-----
Frame( NumBytes ) { |
keyframe | br
if (keyframe && !ConfigurationRecordIsPresent { |
Parameters( ) |
} |
while (remaining_bits_in_bitstream( NumBytes )) { |
Slice( ) |
} |
} |
Architecture overview of slices in a "Frame":
+-----------------------------------------------------------------+
+=================================================================+
| first slice header |
+-----------------------------------------------------------------+
| first slice content |
+-----------------------------------------------------------------+
| first slice footer |
+-----------------------------------------------------------------+
| --------------------------------------------------------------- |
+-----------------------------------------------------------------+
| second slice header |
+-----------------------------------------------------------------+
| second slice content |
+-----------------------------------------------------------------+
| second slice footer |
+-----------------------------------------------------------------+
| --------------------------------------------------------------- |
+-----------------------------------------------------------------+
| ... |
+-----------------------------------------------------------------+
| --------------------------------------------------------------- |
+-----------------------------------------------------------------+
| last slice header |
+-----------------------------------------------------------------+
| last slice content |
+-----------------------------------------------------------------+
| last slice footer |
+-----------------------------------------------------------------+
Table 15
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4.4. Slice
A "Slice" is an independent spatial sub-section of a "Frame" that is
encoded separately from another region of the same "Frame". The use
of more than one "Slice" per "Frame" can be useful for taking
advantage of the opportunities of multithreaded encoding and
decoding.
A "Slice" consists of a "Slice Header" (when relevant), a "Slice
Content", and a "Slice Footer" (when relevant). The pseudo-code
below describes the contents of a "Slice".
pseudo-code | type
--------------------------------------------------------------|-----
Slice( ) { |
if (version >= 3) { |
SliceHeader( ) |
} |
SliceContent( ) |
if (coder_type == 0) { |
while (!byte_aligned()) { |
padding | u(1)
} |
} |
if (version <= 1) { |
while (remaining_bits_in_bitstream( NumBytes ) != 0) {|
reserved | u(1)
} |
} |
if (version >= 3) { |
SliceFooter( ) |
} |
} |
"padding" specifies a bit without any significance and used only for
byte alignment. MUST be 0.
"reserved" specifies a bit without any significance in this revision
of the specification and may have a significance in a later revision
of this specification.
Encoders SHOULD NOT fill these bits.
Decoders SHOULD ignore these bits.
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4.5. Slice Header
A "Slice Header" provides information about the decoding
configuration of the "Slice", such as its spatial position, size, and
aspect ratio. The pseudo-code below describes the contents of the
"Slice Header".
pseudo-code | type
--------------------------------------------------------------|-----
SliceHeader( ) { |
slice_x | ur
slice_y | ur
slice_width - 1 | ur
slice_height - 1 | ur
for (i = 0; i < quant_table_set_index_count; i++) { |
quant_table_set_index[ i ] | ur
} |
picture_structure | ur
sar_num | ur
sar_den | ur
} |
4.5.1. slice_x
"slice_x" indicates the x position on the slice raster formed by
num_h_slices.
Inferred to be 0 if not present.
4.5.2. slice_y
"slice_y" indicates the y position on the slice raster formed by
num_v_slices.
Inferred to be 0 if not present.
4.5.3. slice_width
"slice_width" indicates the width on the slice raster formed by
num_h_slices.
Inferred to be 1 if not present.
4.5.4. slice_height
"slice_height" indicates the height on the slice raster formed by
num_v_slices.
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Inferred to be 1 if not present.
4.5.5. quant_table_set_index_count
"quant_table_set_index_count" is defined as:
1 + ( ( chroma_planes || version <= 3 ) ? 1 : 0 ) + ( extra_plane ? 1
: 0 )
4.5.6. quant_table_set_index
"quant_table_set_index" indicates the Quantization Table Set index to
select the Quantization Table Set and the initial states for the
slice.
Inferred to be 0 if not present.
4.5.7. picture_structure
"picture_structure" specifies the temporal and spatial relationship
of each "Line" of the "Frame".
Inferred to be 0 if not present.
+-------+-------------------------+
| value | picture structure used |
+=======+=========================+
| 0 | unknown |
+-------+-------------------------+
| 1 | top field first |
+-------+-------------------------+
| 2 | bottom field first |
+-------+-------------------------+
| 3 | progressive |
+-------+-------------------------+
| Other | reserved for future use |
+-------+-------------------------+
Table 16
4.5.8. sar_num
"sar_num" specifies the "Sample" aspect ratio numerator.
Inferred to be 0 if not present.
A value of 0 means that aspect ratio is unknown.
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Encoders MUST write 0 if "Sample" aspect ratio is unknown.
If "sar_den" is 0, decoders SHOULD ignore the encoded value and
consider that "sar_num" is 0.
4.5.9. sar_den
"sar_den" specifies the "Sample" aspect ratio denominator.
Inferred to be 0 if not present.
A value of 0 means that aspect ratio is unknown.
Encoders MUST write 0 if "Sample" aspect ratio is unknown.
If "sar_num" is 0, decoders SHOULD ignore the encoded value and
consider that "sar_den" is 0.
4.6. Slice Content
A "Slice Content" contains all "Line" elements part of the "Slice".
Depending on the configuration, "Line" elements are ordered by
"Plane" then by row (YCbCr) or by row then by "Plane" (RGB).
pseudo-code | type
--------------------------------------------------------------|-----
SliceContent( ) { |
if (colorspace_type == 0) { |
for (p = 0; p < primary_color_count; p++) { |
for (y = 0; y < plane_pixel_height[ p ]; y++) { |
Line( p, y ) |
} |
} |
} else if (colorspace_type == 1) { |
for (y = 0; y < slice_pixel_height; y++) { |
for (p = 0; p < primary_color_count; p++) { |
Line( p, y ) |
} |
} |
} |
} |
4.6.1. primary_color_count
"primary_color_count" is defined as:
1 + ( chroma_planes ? 2 : 0 ) + ( extra_plane ? 1 : 0 )
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4.6.2. plane_pixel_height
"plane_pixel_height[ p ]" is the height in "Pixels" of "Plane" p of
the "Slice". It is defined as:
(chroma_planes == 1 && (p == 1 || p == 2)) ? ceil(slice_pixel_height
/ (1 << log2_v_chroma_subsample)) : slice_pixel_height
4.6.3. slice_pixel_height
"slice_pixel_height" is the height in pixels of the slice. It is
defined as:
floor( ( slice_y + slice_height ) * slice_pixel_height / num_v_slices
) - slice_pixel_y.
4.6.4. slice_pixel_y
"slice_pixel_y" is the slice vertical position in pixels. It is
defined as:
floor( slice_y * frame_pixel_height / num_v_slices )
4.7. Line
A "Line" is a list of the sample differences (relative to the
predictor) of primary color components. The pseudo-code below
describes the contents of the "Line".
pseudo-code | type
--------------------------------------------------------------|-----
Line( p, y ) { |
if (colorspace_type == 0) { |
for (x = 0; x < plane_pixel_width[ p ]; x++) { |
sample_difference[ p ][ y ][ x ] | sd
} |
} else if (colorspace_type == 1) { |
for (x = 0; x < slice_pixel_width; x++) { |
sample_difference[ p ][ y ][ x ] | sd
} |
} |
} |
4.7.1. plane_pixel_width
"plane_pixel_width[ p ]" is the width in "Pixels" of "Plane" p of the
"Slice". It is defined as:
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(chroma_planes == 1 && (p == 1 || p == 2)) ? ceil( slice_pixel_width
/ (1 << log2_h_chroma_subsample) ) : slice_pixel_width.
4.7.2. slice_pixel_width
"slice_pixel_width" is the width in "Pixels" of the slice. It is
defined as:
floor( ( slice_x + slice_width ) * slice_pixel_width / num_h_slices )
- slice_pixel_x
4.7.3. slice_pixel_x
"slice_pixel_x" is the slice horizontal position in "Pixels". It is
defined as:
floor( slice_x * frame_pixel_width / num_h_slices )
4.7.4. sample_difference
"sample_difference[ p ][ y ][ x ]" is the sample difference for
"Sample" at "Plane" "p", y position "y", and x position "x". The
"Sample" value is computed based on median predictor and context
described in Section 3.2.
4.8. Slice Footer
A "Slice Footer" provides information about slice size and
(optionally) parity. The pseudo-code below describes the contents of
the "Slice Footer".
Note: "Slice Footer" is always byte aligned.
pseudo-code | type
--------------------------------------------------------------|-----
SliceFooter( ) { |
slice_size | u(24)
if (ec) { |
error_status | u(8)
slice_crc_parity | u(32)
} |
} |
4.8.1. slice_size
"slice_size" indicates the size of the slice in bytes.
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Note: this allows finding the start of slices before previous slices
have been fully decoded, and allows parallel decoding as well as
error resilience.
4.8.2. error_status
"error_status" specifies the error status.
+-------+--------------------------------------+
| value | error status |
+=======+======================================+
| 0 | no error |
+-------+--------------------------------------+
| 1 | slice contains a correctable error |
+-------+--------------------------------------+
| 2 | slice contains a uncorrectable error |
+-------+--------------------------------------+
| Other | reserved for future use |
+-------+--------------------------------------+
Table 17
4.8.3. slice_crc_parity
"slice_crc_parity" 32 bits that are chosen so that the slice as a
whole has a crc remainder of 0.
This is equivalent to storing the crc remainder in the 32-bit parity.
The CRC generator polynomial used is the standard IEEE CRC polynomial
(0x104C11DB7), with initial value 0, without pre-inversion and
without post-inversion.
4.9. Quantization Table Set
The Quantization Table Sets are stored by storing the number of equal
entries -1 of the first half of the table (represented as "len - 1"
in the pseudo-code below) using the method described in
Section 3.8.1.2. The second half doesn't need to be stored as it is
identical to the first with flipped sign. "scale" and "len_count[ i
][ j ]" are temporary values used for the computing of
"context_count[ i ]" and are not used outside Quantization Table Set
pseudo-code.
Example:
Table: 0 0 1 1 1 1 2 2 -2 -2 -2 -1 -1 -1 -1 0
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Stored values: 1, 3, 1
pseudo-code | type
--------------------------------------------------------------|-----
QuantizationTableSet( i ) { |
scale = 1 |
for (j = 0; j < MAX_CONTEXT_INPUTS; j++) { |
QuantizationTable( i, j, scale ) |
scale *= 2 * len_count[ i ][ j ] - 1 |
} |
context_count[ i ] = ceil( scale / 2 ) |
} |
"MAX_CONTEXT_INPUTS" is 5.
pseudo-code | type
--------------------------------------------------------------|-----
QuantizationTable(i, j, scale) { |
v = 0 |
for (k = 0; k < 128;) { |
len - 1 | ur
for (a = 0; a < len; a++) { |
quant_tables[ i ][ j ][ k ] = scale * v |
k++ |
} |
v++ |
} |
for (k = 1; k < 128; k++) { |
quant_tables[ i ][ j ][ 256 - k ] = \ |
-quant_tables[ i ][ j ][ k ] |
} |
quant_tables[ i ][ j ][ 128 ] = \ |
-quant_tables[ i ][ j ][ 127 ] |
len_count[ i ][ j ] = v |
} |
4.9.1. quant_tables
"quant_tables[ i ][ j ][ k ]" indicates the quantification table
value of the Quantized Sample Difference "k" of the Quantization
Table "j" of the Set Quantization Table Set "i".
4.9.2. context_count
"context_count[ i ]" indicates the count of contexts for Quantization
Table Set "i". "context_count[ i ]" MUST be less than or equal to
32768.
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5. Restrictions
To ensure that fast multithreaded decoding is possible, starting with
version 3 and if "frame_pixel_width * frame_pixel_height" is more
than 101376, "slice_width * slice_height" MUST be less or equal to
"num_h_slices * num_v_slices / 4". Note: 101376 is the frame size in
"Pixels" of a 352x288 frame also known as CIF ("Common Intermediate
Format") frame size format.
For each "Frame", each position in the slice raster MUST be filled by
one and only one slice of the "Frame" (no missing slice position, no
slice overlapping).
For each "Frame" with "keyframe" value of 0, each slice MUST have the
same value of "slice_x", "slice_y", "slice_width", "slice_height" as
a slice in the previous "Frame".
6. Security Considerations
Like any other codec, (such as [RFC6716]), FFV1 should not be used
with insecure ciphers or cipher-modes that are vulnerable to known
plaintext attacks. Some of the header bits as well as the padding
are easily predictable.
Implementations of the FFV1 codec need to take appropriate security
considerations into account, as outlined in [RFC4732]. It is
extremely important for the decoder to be robust against malicious
payloads. Malicious payloads must not cause the decoder to overrun
its allocated memory or to take an excessive amount of resources to
decode. The same applies to the encoder, even though problems in
encoders are typically rarer. Malicious video streams must not cause
the encoder to misbehave because this would allow an attacker to
attack transcoding gateways. A frequent security problem in image
and video codecs is also to not check for integer overflows in
"Pixel" count computations, that is to allocate width * height
without considering that the multiplication result may have
overflowed the arithmetic types range. The range coder could, if
implemented naively, read one byte over the end. The implementation
must ensure that no read outside allocated and initialized memory
occurs.
The reference implementation [REFIMPL] contains no known buffer
overflow or cases where a specially crafted packet or video segment
could cause a significant increase in CPU load.
The reference implementation [REFIMPL] was validated in the following
conditions:
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* Sending the decoder valid packets generated by the reference
encoder and verifying that the decoder's output matches the
encoder's input.
* Sending the decoder packets generated by the reference encoder and
then subjected to random corruption.
* Sending the decoder random packets that are not FFV1.
In all of the conditions above, the decoder and encoder was run
inside the [VALGRIND] memory debugger as well as clangs address
sanitizer [Address-Sanitizer], which track reads and writes to
invalid memory regions as well as the use of uninitialized memory.
There were no errors reported on any of the tested conditions.
7. Media Type Definition
This section completes the media type registration template defined
in [RFC6838] and following [RFC4855].
Type name: video
Subtype name: FFV1
Required parameters: None.
Optional parameters:
This parameter is used to signal the capabilities of a receiver
implementation. This parameter MUST NOT be used for any other
purpose.
"version": The "version" of the FFV1 encoding as defined by
Section 4.1.1.
"micro_version": The "micro_version" of the FFV1 encoding as defined
by Section 4.1.2.
"coder_type": The "coder_type" of the FFV1 encoding as defined by
Section 4.1.3.
"colorspace_type": The "colorspace_type" of the FFV1 encoding as
defined by Section 4.1.5.
"bits_per_raw_sample": The "bits_per_raw_sample" of the FFV1 encoding
as defined by Section 4.1.7.
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"max_slices": The value of "max_slices" is an integer indicating the
maximum count of slices with a frames of the FFV1 encoding.
Encoding considerations:
This media type is defined for encapsulation in several audiovisual
container formats and contains binary data; see Section 4.2.3. This
media type is framed binary data; see Section 4.8 of [RFC6838].
Security considerations:
See Section 6 of this document.
Interoperability considerations: None.
Published specification:
RFC XXXX.
[RFC Editor: Upon publication as an RFC, please replace "XXXX" with
the number assigned to this document and remove this note.]
Applications which use this media type:
Any application that requires the transport of lossless video can use
this media type. Some examples are, but not limited to screen
recording, scientific imaging, and digital video preservation.
Fragment identifier considerations: N/A.
Additional information: None.
Person & email address to contact for further information: Michael
Niedermayer michael@niedermayer.cc (mailto:michael@niedermayer.cc)
Intended usage: COMMON
Restrictions on usage: None.
Author: Dave Rice dave@dericed.com (mailto:dave@dericed.com)
Change controller: IETF cellar working group delegated from the IESG.
8. IANA Considerations
The IANA is requested to register the following values:
* Media type registration as described in Section 7.
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9. Changelog
See https://github.com/FFmpeg/FFV1/commits/master
(https://github.com/FFmpeg/FFV1/commits/master)
[RFC Editor: Please remove this Changelog section prior to
publication.]
10. Normative References
[ISO.15444-1.2016]
International Organization for Standardization,
"Information technology -- JPEG 2000 image coding system:
Core coding system", October 2016.
[Matroska] IETF, "Matroska", 2019, .
[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
.
[ISO.9899.2018]
International Organization for Standardization,
"Programming languages - C", 2018.
[RFC6716] Valin, JM., Vos, K., and T. Terriberry, "Definition of the
Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716,
September 2012, .
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
[ISO.9899.1990]
International Organization for Standardization,
"Programming languages - C", 1990.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
11. Informative References
[YCbCr] Wikipedia, "YCbCr", undated,
.
[REFIMPL] Niedermayer, M., "The reference FFV1 implementation / the
FFV1 codec in FFmpeg", undated, .
[Address-Sanitizer]
The Clang Team, "ASAN AddressSanitizer website", undated,
.
[VALGRIND] Valgrind Developers, "Valgrind website", undated,
.
[ISO.14495-1.1999]
International Organization for Standardization,
"Information technology -- Lossless and near-lossless
compression of continuous-tone still images: Baseline",
December 1999.
[ISO.14496-10.2014]
International Organization for Standardization,
"Information technology -- Coding of audio-visual objects
-- Part 10: Advanced Video Coding", September 2014.
[ISO.14496-12.2015]
International Organization for Standardization,
"Information technology -- Coding of audio-visual objects
-- Part 12: ISO base media file format", December 2015.
[HuffYUV] Rudiak-Gould, B., "HuffYUV", December 2003,
.
[AVI] Microsoft, "AVI RIFF File Reference", undated,
.
[NUT] Niedermayer, M., "NUT Open Container Format", December
2013, .
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[FFV1_V3] Niedermayer, M., "Commit to mark FFV1 version 3 as non-
experimental", August 2013, .
[range-coding]
Nigel, G. and N. Martin, "Range encoding: an algorithm for
removing redundancy from a digitised message.", July 1979.
[FFV1_V0] Niedermayer, M., "Commit to mark FFV1 version 0 as non-
experimental", April 2006, .
[FFV1_V1] Niedermayer, M., "Commit to release FFV1 version 1", April
2009, .
Appendix A. Multi-theaded decoder implementation suggestions
This appendix is informative.
The FFV1 bitstream is parsable in two ways: in sequential order as
described in this document or with the pre-analysis of the footer of
each slice. Each slice footer contains a "slice_size" field so the
boundary of each slice is computable without having to parse the
slice content. That allows multi-threading as well as independence
of slice content (a bitstream error in a slice header or slice
content has no impact on the decoding of the other slices).
After having checked "keyframe" field, a decoder SHOULD parse
"slice_size" fields, from "slice_size" of the last slice at the end
of the "Frame" up to "slice_size" of the first slice at the beginning
of the "Frame", before parsing slices, in order to have slices
boundaries. A decoder MAY fallback on sequential order e.g. in case
of a corrupted "Frame" (frame size unknown, "slice_size" of slices
not coherent...) or if there is no possibility of seeking into the
stream.
Appendix B. Future handling of some streams created by non conforming
encoders
This appendix is informative.
Some bitstreams were found with 40 extra bits corresponding to
"error_status" and "slice_crc_parity" in the "reserved" bits of
"Slice()". Any revision of this specification SHOULD care about
avoiding to add 40 bits of content after "SliceContent" if "version"
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== 0 or "version" == 1. Else a decoder conforming to the revised
specification could not distinguish between a revised bitstream and
such buggy bitstream in the wild.
Authors' Addresses
Michael Niedermayer
Email: michael@niedermayer.cc
Dave Rice
Email: dave@dericed.com
Jerome Martinez
Email: jerome@mediaarea.net
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