FFV1 Video Coding Format Version 4
draft-ietf-cellar-ffv1-v4-17
cellar M. Niedermayer
Internet-Draft
Intended status: Standards Track D. Rice
Expires: 26 November 2021
J. Martinez
25 May 2021
FFV1 Video Coding Format Version 4
draft-ietf-cellar-ffv1-v4-17
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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 November 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
Niedermayer, et al. Expires 26 November 2021 [Page 1]
Internet-Draft FFV1 May 2021
This document is subject to BCP 78 and the IETF Trust's Legal
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
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Notation and Conventions . . . . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . . . . . 7
2.2.4. Comparison Operators . . . . . . . . . . . . . . . . 7
2.2.5. Mathematical Functions . . . . . . . . . . . . . . . 7
2.2.6. Order of Operation Precedence . . . . . . . . . . . . 8
2.2.7. Range . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.8. NumBytes . . . . . . . . . . . . . . . . . . . . . . 9
2.2.9. Bitstream Functions . . . . . . . . . . . . . . . . . 9
3. Sample Coding . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Border . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Samples . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Median Predictor . . . . . . . . . . . . . . . . . . . . 11
3.3.1. Exception . . . . . . . . . . . . . . . . . . . . . . 11
3.4. Quantization Table Sets . . . . . . . . . . . . . . . . . 12
3.5. Context . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.6. Quantization Table Set Indexes . . . . . . . . . . . . . 13
3.7. Color spaces . . . . . . . . . . . . . . . . . . . . . . 13
3.7.1. YCbCr . . . . . . . . . . . . . . . . . . . . . . . . 13
3.7.2. RGB . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.8. Coding of the Sample Difference . . . . . . . . . . . . . 16
3.8.1. Range Coding Mode . . . . . . . . . . . . . . . . . . 16
3.8.2. Golomb Rice Mode . . . . . . . . . . . . . . . . . . 23
4. Bitstream . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1. Quantization Table Set . . . . . . . . . . . . . . . . . 30
4.1.1. quant_tables . . . . . . . . . . . . . . . . . . . . 31
4.1.2. context_count . . . . . . . . . . . . . . . . . . . . 32
4.2. Parameters . . . . . . . . . . . . . . . . . . . . . . . 32
4.2.1. version . . . . . . . . . . . . . . . . . . . . . . . 34
4.2.2. micro_version . . . . . . . . . . . . . . . . . . . . 34
4.2.3. coder_type . . . . . . . . . . . . . . . . . . . . . 35
4.2.4. state_transition_delta . . . . . . . . . . . . . . . 36
4.2.5. colorspace_type . . . . . . . . . . . . . . . . . . . 36
Niedermayer, et al. Expires 26 November 2021 [Page 2]
Internet-Draft FFV1 May 2021
4.2.6. chroma_planes . . . . . . . . . . . . . . . . . . . . 37
4.2.7. bits_per_raw_sample . . . . . . . . . . . . . . . . . 37
4.2.8. log2_h_chroma_subsample . . . . . . . . . . . . . . . 38
4.2.9. log2_v_chroma_subsample . . . . . . . . . . . . . . . 38
4.2.10. extra_plane . . . . . . . . . . . . . . . . . . . . . 38
4.2.11. num_h_slices . . . . . . . . . . . . . . . . . . . . 38
4.2.12. num_v_slices . . . . . . . . . . . . . . . . . . . . 39
4.2.13. quant_table_set_count . . . . . . . . . . . . . . . . 39
4.2.14. states_coded . . . . . . . . . . . . . . . . . . . . 39
4.2.15. initial_state_delta . . . . . . . . . . . . . . . . . 39
4.2.16. ec . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.2.17. intra . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3. Configuration Record . . . . . . . . . . . . . . . . . . 40
4.3.1. reserved_for_future_use . . . . . . . . . . . . . . . 41
4.3.2. configuration_record_crc_parity . . . . . . . . . . . 41
4.3.3. Mapping FFV1 into Containers . . . . . . . . . . . . 41
4.4. Frame . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.5. Slice . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.6. Slice Header . . . . . . . . . . . . . . . . . . . . . . 45
4.6.1. slice_x . . . . . . . . . . . . . . . . . . . . . . . 45
4.6.2. slice_y . . . . . . . . . . . . . . . . . . . . . . . 45
4.6.3. slice_width . . . . . . . . . . . . . . . . . . . . . 45
4.6.4. slice_height . . . . . . . . . . . . . . . . . . . . 46
4.6.5. quant_table_set_index_count . . . . . . . . . . . . . 46
4.6.6. quant_table_set_index . . . . . . . . . . . . . . . . 46
4.6.7. picture_structure . . . . . . . . . . . . . . . . . . 46
4.6.8. sar_num . . . . . . . . . . . . . . . . . . . . . . . 47
4.6.9. sar_den . . . . . . . . . . . . . . . . . . . . . . . 47
4.6.10. reset_contexts . . . . . . . . . . . . . . . . . . . 47
4.6.11. slice_coding_mode . . . . . . . . . . . . . . . . . . 47
4.7. Slice Content . . . . . . . . . . . . . . . . . . . . . . 48
4.7.1. primary_color_count . . . . . . . . . . . . . . . . . 48
4.7.2. plane_pixel_height . . . . . . . . . . . . . . . . . 48
4.7.3. slice_pixel_height . . . . . . . . . . . . . . . . . 49
4.7.4. slice_pixel_y . . . . . . . . . . . . . . . . . . . . 49
4.8. Line . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.8.1. plane_pixel_width . . . . . . . . . . . . . . . . . . 49
4.8.2. slice_pixel_width . . . . . . . . . . . . . . . . . . 50
4.8.3. slice_pixel_x . . . . . . . . . . . . . . . . . . . . 50
4.8.4. sample_difference . . . . . . . . . . . . . . . . . . 50
4.9. Slice Footer . . . . . . . . . . . . . . . . . . . . . . 50
4.9.1. slice_size . . . . . . . . . . . . . . . . . . . . . 51
4.9.2. error_status . . . . . . . . . . . . . . . . . . . . 51
4.9.3. slice_crc_parity . . . . . . . . . . . . . . . . . . 51
5. Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 51
6. Security Considerations . . . . . . . . . . . . . . . . . . . 52
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 52
7.1. Media Type Definition . . . . . . . . . . . . . . . . . . 52
Niedermayer, et al. Expires 26 November 2021 [Page 3]
Internet-Draft FFV1 May 2021
8. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 54
9. Normative References . . . . . . . . . . . . . . . . . . . . 54
10. Informative References . . . . . . . . . . . . . . . . . . . 55
Appendix A. Multi-theaded decoder implementation suggestions . . 56
Appendix B. Future handling of some streams created by non
conforming encoders . . . . . . . . . . . . . . . . . . . 57
Appendix C. FFV1 Implementations . . . . . . . . . . . . . . . . 57
C.1. FFmpeg FFV1 Codec . . . . . . . . . . . . . . . . . . . . 57
C.2. FFV1 Decoder in Go . . . . . . . . . . . . . . . . . . . 57
C.3. MediaConch . . . . . . . . . . . . . . . . . . . . . . . 58
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 58
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 a version 4 of FFV1. Prior versions of FFV1
are defined within [I-D.ietf-cellar-ffv1].
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.
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.
Niedermayer, et al. Expires 26 November 2021 [Page 4]
Internet-Draft FFV1 May 2021
2.1. Definitions
"FFV1": chosen name of this video encoding format, short version of
"FF Video 1", the letters "FF" coming from "FFmpeg", the name of the
reference decoder, whose first letters originally meant "Fast
Forward".
"Container": Format that encapsulates Frames (see Section 4.4) 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 (Y), Blue-difference Chroma (Cb), Red-difference Chroma (Cr),
Transparency, Red, Green, and Blue.
"Symbol": A value stored in the bitstream, which is defined and
decoded through one of the methods described in Table 4.
"Line": A discrete component of a static image composed of Samples
that represent a specific quantification of Samples of that image.
"Plane": A discrete component of a static image composed of Lines
that represent a specific quantification of Lines of that image.
"Pixel": The smallest addressable representation of a color in a
Frame. It is composed of one or more Samples.
"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 chroma 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 chroma Samples, e.g. YCbCr, YCgCo or ICtCp.
The exact meaning of the three numeric values is unspecified.
"TBA": To Be Announced. Used in reference to the development of
future iterations of the FFV1 specification.
2.2. Conventions
Niedermayer, et al. Expires 26 November 2021 [Page 5]
Internet-Draft FFV1 May 2021
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.9899.2018] and uses its "if/else", "while" and "for"
keywords as well as functions defined within this document.
In some instances, pseudo-code is presented in a two-column format
such as shown in Figure 1. In this form the "type" column provides a
Symbol as defined in Table 4 that defines the storage of the data
referenced in that same line of pseudo-code.
pseudo-code | type
--------------------------------------------------------------|-----
ExamplePseudoCode( ) { |
value | ur
} |
Figure 1: A depiction of type-labelled pseudo-code used 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.
Niedermayer, et al. Expires 26 November 2021 [Page 6]
Internet-Draft FFV1 May 2021
"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.
"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" is true when a is greater than b.
"a >= b" is true when a is greater than or equal to b.
"a < b" is true when a is less than b.
"a <= b" is true when a is less than or equal b.
"a == b" is true when a is equal to b.
"a != b" is true when a is not equal to b.
"a && b" is true when both a is true and b is true.
"a || b" is true when either a is true or b is true.
"!a" is true when a is not true.
"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.
Niedermayer, et al. Expires 26 November 2021 [Page 7]
Internet-Draft FFV1 May 2021
"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 smaller of two values a and b.
"max(a,b)" means the larger 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 A implies B.
"A <==> B" means A ==> B , B ==> A.
a_b means the b-th value of a sequence of a
a_(b,c) means the 'b,c'-th value of a sequence of 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 : c
a = b, a += b, a -= b, a *= b
Niedermayer, et al. Expires 26 November 2021 [Page 8]
Internet-Draft FFV1 May 2021
2.2.7. Range
"a...b" means any value 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 4.3.3.
2.2.9. Bitstream Functions
2.2.9.1. remaining_bits_in_bitstream
"remaining_bits_in_bitstream( NumBytes )" 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.
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 4.5) 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.
Niedermayer, et al. Expires 26 November 2021 [Page 9]
Internet-Draft FFV1 May 2021
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 2 depicts a slice of 9 Samples "a,b,c,d,e,f,g,h,i" in a 3x3
arrangement along with its assumed border.
+---+---+---+---+---+---+---+---+
| 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 2: 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 3. The labels for these relatively
positioned Samples are used within the median predictor and context.
Niedermayer, et al. Expires 26 November 2021 [Page 10]
Internet-Draft FFV1 May 2021
+---+---+---+---+
| | | T | |
+---+---+---+---+
| |tl | t |tr |
+---+---+---+---+
| L | l | X | |
+---+---+---+---+
Figure 3: A depiction of how relatively positioned Samples are
referenced 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)
Note, this prediction template is also used in [ISO.14495-1.1999] and
[HuffYUV].
3.3.1. Exception
If "colorspace_type == 0 && bits_per_raw_sample == 16 && ( coder_type
== 1 || coder_type == 2 )" (see Section 4.2.5, Section 4.2.7 and
Section 4.2.3), 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 16-bit signed integer was used for
storing Sample values in all known implementations of FFV1 bitstream
(see Appendix C). 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
Niedermayer, et al. Expires 26 November 2021 [Page 11]
Internet-Draft FFV1 May 2021
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. Quantization Table Sets
Quantization Tables are used on Sample Differences (see Section 3.8),
so Quantized Sample Differences are stored in the bitstream.
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 (see
Section 4.1.1).
3.5. 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 5
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.
Niedermayer, et al. Expires 26 November 2021 [Page 12]
Internet-Draft FFV1 May 2021
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.
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
Niedermayer, et al. Expires 26 November 2021 [Page 13]
Internet-Draft FFV1 May 2021
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
Figure 6: Description of the transformation of pixels from RGB
color space to coded modified YCbCr color space.
g = Y - (Cb + Cr) >> 2
r = Cr + g
b = Cb + g
Figure 7: Description of the transformation of pixels from coded
modified YCbCr color space to RGB color space.
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:
Niedermayer, et al. Expires 26 November 2021 [Page 14]
Internet-Draft FFV1 May 2021
+------------------------+------------------------+
| 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) |
+------------------------+------------------------+
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)
3.7.2.1. Exception
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
Figure 8: Description of the transformation of pixels from RGB
color space to coded modified YCbCr color space (in case of
exception).
b = Y - (Cb + Cr) >> 2
r = Cr + b
g = Cb + b
Figure 9: Description of the transformation of pixels from coded
modified YCbCr color space to RGB color space (in case of
exception).
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.
Niedermayer, et al. Expires 26 November 2021 [Page 15]
Internet-Draft FFV1 May 2021
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 10: Description of the coding of the Sample Difference in
the bitstream.
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 N. Martin in 1979 [range-coding].
3.8.1.1. Range Binary Values
To encode binary digits efficiently a Range coder is used. A Range
coder encodes a series of binary symbols by using a probability
estimation within each context. The sizes of each of the 2 sub-
ranges are proportional to their estimated probability. The
quantization table is used to choose the context used from the
surrounding image sample values for the case of coding the sample
differences. Coding integers is done by coding multiple binary
values. The range decoder will read bytes until it can determine
which sub-range the input falls into to return the next binary
symbol.
To describe Range coding for FFV1 the following values are used:
C_i the i-th Context.
B_i the i-th byte of the bytestream.
R_i the Range at the i-th symbol.
r_i the boundary between two sub-ranges of R_i: a sub-range of r_i
values and a sub-range R_i - r_i values.
L_i the Low value of the Range at the i-th symbol.
Niedermayer, et al. Expires 26 November 2021 [Page 16]
Internet-Draft FFV1 May 2021
l_i a temporary variable to carry-over or adjust the Low value of
the Range between range coding operations.
t_i a temporary variable to transmit sub-ranges between range coding
operations.
b_i the i-th Range coded binary value.
S_(0, i) the i-th initial state.
j_n the length of the bytestream encoding n binary symbols.
The following Range coder state variables are initialized to the
following values. The Range is initialized to a value of 65,280
(expressed in base 16 as 0xFF00) as depicted in Figure 11. The Low
is initialized according to the value of the first two bytes as
depicted in Figure 12. j_i tracks the length of the bytestream
encoding while incremening from an initial value of j_0 to a final
value of j_n. j_0 is initialized to 2 as depicted in Figure 13.
R_(0) = 65280
Figure 11: The initial value for "Range".
L_(0) = 2 ^ 8 * B_(0) + B_(1)
Figure 12: The initial value for "Low" is set according to the
first two bytes of the bytestream.
j_(0) = 2
Figure 13: The initial value for "j", the length of the
bytestream encoding.
The following equations define how the Range coder variables evolve
as it reads or writes symbols.
r_(i) = floor( ( R_(i) * S_(i, C_(i)) ) / 2 ^ 8 )
Figure 14: This formula shows the positioning of range split
based on the State.
Niedermayer, et al. Expires 26 November 2021 [Page 17]
Internet-Draft FFV1 May 2021
b_(i) = 0 <==>
L_(i) < R_(i) - r_(i) ==>
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) = 1 <==>
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)
Figure 15: This formula shows the linking of the decoded symbol
(represented as b_i), the updated State (represented as
S_(i+1,C_(i))), and the updated range (represented as a range
from l_i to t_i).
C_(i) != k ==> S_(i + 1, k) = S_(i, k)
Figure 16: If the value of "k" is unequal to the i-th value of
Context, in other words if the State is unchanged from the last
symbol coding, then the value of the State is carried over to the
next symbol coding.
t_(i) < 2 ^ 8 ==>
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)
Figure 17: This formula shows the linking of the Range coder with
the reading or writing of the bytestream.
range = 0xFF00;
end = 0;
low = get_bits(16);
if (low >= range) {
low = range;
end = 1;
}
Figure 18: A pseudo-code description of the initialization of
Range coder variables in Range Binary mode.
Niedermayer, et al. Expires 26 November 2021 [Page 18]
Internet-Draft FFV1 May 2021
refill() {
if (range < 256) {
range = range * 256;
low = low * 256;
if (!end) {
c.low += get_bits(8);
if (remaining_bits_in_bitstream( NumBytes ) == 0) {
end = 1;
}
}
}
}
Figure 19: A pseudo-code description of refilling the Range
Binary Value coder buffer.
get_rac(state) {
rangeoff = (range * state) / 256;
range -= rangeoff;
if (low < range) {
state = zero_state[state];
refill();
return 0;
} else {
low -= range;
state = one_state[state];
range = rangeoff;
refill();
return 1;
}
}
Figure 20: A pseudo-code description of the read of a binary
value in Range Binary mode.
3.8.1.1.1. Termination
The range coder can be used in three modes.
* 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.
Niedermayer, et al. Expires 26 November 2021 [Page 19]
Internet-Draft FFV1 May 2021
* 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 21.
Niedermayer, et al. Expires 26 November 2021 [Page 20]
Internet-Draft FFV1 May 2021
int get_symbol(RangeCoder *c, uint8_t *state, int is_signed) {
if (get_rac(c, state + 0) {
return 0;
}
int e = 0;
while (get_rac(c, state + 1 + min(e, 9)) { //1..10
e++;
}
int a = 1;
for (int i = e - 1; i >= 0; i--) {
a = a * 2 + get_rac(c, state + 22 + min(i, 9)); // 22..31
}
if (!is_signed) {
return a;
}
if (get_rac(c, state + 11 + min(e, 10))) { //11..21
return -a;
} else {
return a;
}
}
Figure 21: A pseudo-code description of the contexts of Range Non
Binary Values.
"get_symbol" is used for the read out of "sample_difference"
indicated in Figure 10.
"get_rac" returns a boolean, computed from the bytestream as
described in Figure 14 as a formula and in Figure 20 as pseudo-code.
3.8.1.3. Initial Values for the Context Model
When "keyframe" (see Section 4.4) value is 1, all Range coder state
variables are set to their initial state.
3.8.1.4. State Transition Table
In this mode a State Transition Table is used, indicating in which
state the decoder will move to, based on the current state and the
value extracted from Figure 20.
one_state_(i) =
default_state_transition_(i) + state_transition_delta_(i)
Niedermayer, et al. Expires 26 November 2021 [Page 21]
Internet-Draft FFV1 May 2021
Figure 22
zero_state_(i) = 256 - one_state_(256-i)
Figure 23
3.8.1.5. default_state_transition
By default, the following State Transition Table is used:
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,
Niedermayer, et al. Expires 26 November 2021 [Page 22]
Internet-Draft FFV1 May 2021
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 4.2.3) MUST be set
to 2 and the difference to the default MUST be stored in the
"Parameters", see Section 4.2. The reference implementation of FFV1
in FFmpeg uses Figure 24 by default at the time of this writing when
Range coding is used.
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 24: Alternative state transition table for Range coding.
3.8.2. Golomb Rice Mode
The end of the bitstream of the Frame is padded with 0-bits until the
bitstream contains a multiple of 8 bits.
Niedermayer, et al. Expires 26 November 2021 [Page 23]
Internet-Draft FFV1 May 2021
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.
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;
}
Figure 25: A pseudo-code description of the read of an unsigned
integer in Golomb Rice mode.
int get_sr_golomb(k) {
v = get_ur_golomb(k);
if (v & 1) return - (v >> 1) - 1;
else return (v >> 1);
}
Figure 26: A pseudo-code description of the read of a signed
integer in Golomb Rice mode.
Niedermayer, et al. Expires 26 November 2021 [Page 24]
Internet-Draft FFV1 May 2021
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
"ESC" is 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.
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
Table 3 shows practical examples of how Signed Golomb Rice Codes are
decoded based on the series of bits extracted from the bitstream as
described by the method above:
Niedermayer, et al. Expires 26 November 2021 [Page 25]
Internet-Draft FFV1 May 2021
+=====+=======================+=======+
| 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: Examples of decoded Signed
Golomb Rice Codes.
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 sample difference is identical to the
predicted one. The run and the first different sample difference are
coded as defined in Section 3.8.2.4.1.
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.
Niedermayer, et al. Expires 26 November 2021 [Page 26]
Internet-Draft FFV1 May 2021
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. Sign extension
"sign_extend" is the function of increasing the number of bits of an
input binary number in twos complement signed number representation
while preserving the input number's sign (positive/negative) and
value, in order to fit in the output bit width. It MAY be computed
with:
sign_extend(input_number, input_bits) {
negative_bias = 1 << (input_bits - 1);
bits_mask = negative_bias - 1;
output_number = input_number & bits_mask; // Remove negative bit
is_negative = input_number & negative_bias; // Test negative bit
if (is_negative)
output_number -= negative_bias;
return output_number
}
Niedermayer, et al. Expires 26 November 2021 [Page 27]
Internet-Draft FFV1 May 2021
3.8.2.4. Scalar Mode
Each difference is coded with the per context mean prediction removed
and a per context value for k.
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;
}
3.8.2.4.1. Golomb Rice Sample Difference Coding
Level coding is identical to the normal difference coding with the
exception that the 0 value is removed as it cannot occur:
Niedermayer, et al. Expires 26 November 2021 [Page 28]
Internet-Draft FFV1 May 2021
diff = get_vlc_symbol(context_state);
if (diff >= 0) {
diff++;
}
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.
3.8.2.5. Initial Values for the VLC context state
When "keyframe" (see Section 4.4) value is 1, all VLC 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, as described
in Section 2.2.1, to explain the structure of each FFV1 bitstream
component. 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.
Niedermayer, et al. Expires 26 November 2021 [Page 29]
Internet-Draft FFV1 May 2021
+========+=================================================+
| Symbol | Definition |
+========+=================================================+
| u(n) | unsigned big endian integer Symbol 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 Symbol coded with the method |
| | described in Section 3.8 |
+--------+-------------------------------------------------+
Table 4: Definition of pseudo-code symbols for this
document.
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. 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:
Niedermayer, et al. Expires 26 November 2021 [Page 30]
Internet-Draft FFV1 May 2021
Table: 0 0 1 1 1 1 2 2 -2 -2 -2 -1 -1 -1 -1 0
Stored values: 1, 3, 1
"QuantizationTableSet" has its own initial states, all set to 128.
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 (n = 0; n < len; n++) { |
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 |
} |
4.1.1. quant_tables
"quant_tables[ i ][ j ][ k ]" indicates the quantization table value
of the Quantized Sample Difference "k" of the Quantization Table "j"
of the Quantization Table Set "i".
Niedermayer, et al. Expires 26 November 2021 [Page 31]
Internet-Draft FFV1 May 2021
4.1.2. 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.
4.2. 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 27 describes the contents of the bitstream.
"Parameters" has its own initial states, all set to 128.
Niedermayer, et al. Expires 26 November 2021 [Page 32]
Internet-Draft FFV1 May 2021
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 27: A pseudo-code description of the bitstream contents.
CONTEXT_SIZE is 32.
Niedermayer, et al. Expires 26 November 2021 [Page 33]
Internet-Draft FFV1 May 2021
4.2.1. 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 |
+-------+-------------------------+
| 4 | FFV1 version 4 |
+-------+-------------------------+
| Other | reserved for future use |
+-------+-------------------------+
Table 5
* Version 2 was experimental and this document does not describe it.
4.2.2. 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:
Niedermayer, et al. Expires 26 November 2021 [Page 34]
Internet-Draft FFV1 May 2021
+=======+=========================+
| 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.
Meaning of "micro_version" for "version" 4 (note: at the time of
writing of this specification, version 4 is not considered stable so
the first stable "micro_version" value is to be announced in the
future):
+=========+=========================+
| value | micro_version |
+=========+=========================+
| 0...TBA | reserved* |
+---------+-------------------------+
| TBA | first stable variant |
+---------+-------------------------+
| Other | reserved for future use |
+---------+-------------------------+
Table 7: The definitions for
"micro_version" values for FFV1
version 4.
* development versions which may be incompatible with the stable
variants.
4.2.3. coder_type
"coder_type" specifies the coder used.
Niedermayer, et al. Expires 26 November 2021 [Page 35]
Internet-Draft FFV1 May 2021
+=======+=================================================+
| 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 8
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.
4.2.4. state_transition_delta
"state_transition_delta" specifies the Range coder custom state
transition table.
If "state_transition_delta" is not present in the FFV1 bitstream, all
Range coder custom state transition table elements are assumed to be
0.
4.2.5. 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.
Niedermayer, et al. Expires 26 November 2021 [Page 36]
Internet-Draft FFV1 May 2021
+=======+==============+================+==============+============+
| 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 9
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.
4.2.6. 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 10
4.2.7. bits_per_raw_sample
"bits_per_raw_sample" indicates the number of bits for each Sample.
Inferred to be 8 if not present.
Niedermayer, et al. Expires 26 November 2021 [Page 37]
Internet-Draft FFV1 May 2021
+=======+=================================+
| value | bits for each sample |
+=======+=================================+
| 0 | reserved* |
+-------+---------------------------------+
| Other | the actual bits for each Sample |
+-------+---------------------------------+
Table 11
* Encoders MUST NOT store "bits_per_raw_sample" = 0. Decoders SHOULD
accept and interpret "bits_per_raw_sample" = 0 as 8.
4.2.8. log2_h_chroma_subsample
"log2_h_chroma_subsample" indicates the subsample factor, stored in
powers to which the number 2 is raised, between luma and chroma width
("chroma_width = 2 ^ -log2_h_chroma_subsample * luma_width").
4.2.9. log2_v_chroma_subsample
"log2_v_chroma_subsample" indicates the subsample factor, stored in
powers to which the number 2 is raised, between luma and chroma
height ("chroma_height = 2 ^ -log2_v_chroma_subsample *
luma_height").
4.2.10. 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 12
4.2.11. num_h_slices
"num_h_slices" indicates the number of horizontal elements of the
slice raster.
Inferred to be 1 if not present.
Niedermayer, et al. Expires 26 November 2021 [Page 38]
Internet-Draft FFV1 May 2021
4.2.12. num_v_slices
"num_v_slices" indicates the number of vertical elements of the slice
raster.
Inferred to be 1 if not present.
4.2.13. 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.
4.2.14. 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 13
4.2.15. 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
Figure 28
initial_state[ i ][ j ][ k ] =
( pred + initial_state_delta[ i ][ j ][ k ] ) & 255
Figure 29
Niedermayer, et al. Expires 26 November 2021 [Page 39]
Internet-Draft FFV1 May 2021
4.2.16. ec
"ec" indicates the error detection/correction type.
+=======+=================================================+
| value | error detection/correction type |
+=======+=================================================+
| 0 | 32-bit CRC in "ConfigurationRecord" |
+-------+-------------------------------------------------+
| 1 | 32-bit CRC in "Slice" and "ConfigurationRecord" |
+-------+-------------------------------------------------+
| Other | reserved for future use |
+-------+-------------------------------------------------+
Table 14
4.2.17. 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 15
4.3. Configuration Record
In the case of a FFV1 bitstream with "version >= 3", a "Configuration
Record" is stored in the underlying Container as described in
Section 4.3.3. It contains the "Parameters" used for all instances
of Frame. The size of the "Configuration Record", "NumBytes", is
supplied by the underlying Container.
Niedermayer, et al. Expires 26 November 2021 [Page 40]
Internet-Draft FFV1 May 2021
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)
} |
4.3.1. reserved_for_future_use
"reserved_for_future_use" is a placeholder for future updates of this
specification.
Encoders conforming to this version of this specification SHALL NOT
write "reserved_for_future_use".
Decoders conforming to this version of this specification SHALL
ignore "reserved_for_future_use".
4.3.2. 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 4.9.3.
4.3.3. 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:
4.3.3.1. 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.
Niedermayer, et al. Expires 26 November 2021 [Page 41]
Internet-Draft FFV1 May 2021
"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.
4.3.3.2. 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.
4.3.3.3. 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".
4.3.3.4. 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.
4.4. Frame
A Frame is an encoded representation of a complete static image. The
whole Frame is provided by the underlaying container.
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.
"keyframe" field has its own initial state, set to 128.
Niedermayer, et al. Expires 26 November 2021 [Page 42]
Internet-Draft FFV1 May 2021
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 16
Niedermayer, et al. Expires 26 November 2021 [Page 43]
Internet-Draft FFV1 May 2021
4.5. 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 "reserved".
Decoders SHOULD ignore "reserved".
Niedermayer, et al. Expires 26 November 2021 [Page 44]
Internet-Draft FFV1 May 2021
4.6. 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".
"Slice Header" has its own initial states, all set to 128.
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
if (version >= 4) { |
reset_contexts | br
slice_coding_mode | ur
} |
} |
4.6.1. slice_x
"slice_x" indicates the x position on the slice raster formed by
num_h_slices.
Inferred to be 0 if not present.
4.6.2. slice_y
"slice_y" indicates the y position on the slice raster formed by
num_v_slices.
Inferred to be 0 if not present.
4.6.3. slice_width
"slice_width" indicates the width on the slice raster formed by
num_h_slices.
Inferred to be 1 if not present.
Niedermayer, et al. Expires 26 November 2021 [Page 45]
Internet-Draft FFV1 May 2021
4.6.4. slice_height
"slice_height" indicates the height on the slice raster formed by
num_v_slices.
Inferred to be 1 if not present.
4.6.5. quant_table_set_index_count
"quant_table_set_index_count" is defined as:
1 + ( ( chroma_planes || version <= 3 ) ? 1 : 0 )
+ ( extra_plane ? 1 : 0 )
4.6.6. 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 Content".
Inferred to be 0 if not present.
4.6.7. 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 17
Niedermayer, et al. Expires 26 November 2021 [Page 46]
Internet-Draft FFV1 May 2021
4.6.8. 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.
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.
4.6.9. 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.
4.6.10. reset_contexts
"reset_contexts" indicates if slice contexts MUST be reset.
Inferred to be 0 if not present.
4.6.11. slice_coding_mode
"slice_coding_mode" indicates the slice coding mode.
Inferred to be 0 if not present.
Niedermayer, et al. Expires 26 November 2021 [Page 47]
Internet-Draft FFV1 May 2021
+=======+=============================+
| value | slice coding mode |
+=======+=============================+
| 0 | Range Coding or Golomb Rice |
+-------+-----------------------------+
| 1 | raw PCM |
+-------+-----------------------------+
| Other | reserved for future use |
+-------+-----------------------------+
Table 18
4.7. 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 ) |
} |
} |
} |
} |
4.7.1. primary_color_count
"primary_color_count" is defined as:
1 + ( chroma_planes ? 2 : 0 ) + ( extra_plane ? 1 : 0 )
4.7.2. plane_pixel_height
"plane_pixel_height[ p ]" is the height in Pixels of Plane p of the
"Slice". It is defined as:
Niedermayer, et al. Expires 26 November 2021 [Page 48]
Internet-Draft FFV1 May 2021
chroma_planes == 1 && (p == 1 || p == 2)
? ceil(slice_pixel_height / (1 << log2_v_chroma_subsample))
: slice_pixel_height
4.7.3. 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.
4.7.4. 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 )
4.8. 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
} |
} |
} |
4.8.1. plane_pixel_width
"plane_pixel_width[ p ]" is the width in Pixels of Plane p of the
"Slice". It is defined as:
Niedermayer, et al. Expires 26 November 2021 [Page 49]
Internet-Draft FFV1 May 2021
chroma_planes == 1 && (p == 1 || p == 2)
? ceil( slice_pixel_width / (1 << log2_h_chroma_subsample) )
: slice_pixel_width.
4.8.2. 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
4.8.3. 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 )
4.8.4. 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.
4.9. 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)
} |
} |
Niedermayer, et al. Expires 26 November 2021 [Page 50]
Internet-Draft FFV1 May 2021
4.9.1. slice_size
"slice_size" indicates the size of the slice in bytes.
Note: this allows finding the start of slices before previous slices
have been fully decoded, and allows parallel decoding as well as
error resilience.
4.9.2. 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 19
4.9.3. 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.
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.
Niedermayer, et al. Expires 26 November 2021 [Page 51]
Internet-Draft FFV1 May 2021
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, except if "reset_contexts" is 1.
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. Those related to denial of service are
outlined in Section 2.1 of [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. An overrun in
allocated memory could lead to arbitrary code execution by an
attacker. 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 failure to check for integer overflows. An
example is allocating "frame_pixel_width * frame_pixel_height" in
Pixel count computations 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.
None of the content carried in FFV1 is intended to be executable.
7. IANA Considerations
The IANA is requested to register the following values:
7.1. Media Type Definition
This registration is done using the template defined in [RFC6838] and
following [RFC4855].
Type name: video
Subtype name: FFV1
Niedermayer, et al. Expires 26 November 2021 [Page 52]
Internet-Draft FFV1 May 2021
Required parameters: None.
Optional parameters: These parameters are used to signal the
capabilities of a receiver implementation. These parameters MUST NOT
be used for any other purpose.
* "version": The "version" of the FFV1 encoding as defined by
Section 4.2.1.
* "micro_version": The "micro_version" of the FFV1 encoding as
defined by Section 4.2.2.
* "coder_type": The "coder_type" of the FFV1 encoding as defined by
Section 4.2.3.
* "colorspace_type": The "colorspace_type" of the FFV1 encoding as
defined by Section 4.2.5.
* "bits_per_raw_sample": The "bits_per_raw_sample" of the FFV1
encoding as defined by Section 4.2.7.
* "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 4.3.3. 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.
Niedermayer, et al. Expires 26 November 2021 [Page 53]
Internet-Draft FFV1 May 2021
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. 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.]
9. Normative References
[ISO.15444-1.2016]
International Organization for Standardization,
"Information technology -- JPEG 2000 image coding system:
Core coding system", October 2016.
[ISO.9899.2018]
International Organization for Standardization,
"Programming languages - C", ISO Standard 9899, 2018.
[Matroska] IETF, "Matroska", 2019, <https://datatracker.ietf.org/doc/
draft-ietf-cellar-matroska/>.
[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/info/rfc2119>.
[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
<https://www.rfc-editor.org/info/rfc4732>.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
<https://www.rfc-editor.org/info/rfc4855>.
Niedermayer, et al. Expires 26 November 2021 [Page 54]
Internet-Draft FFV1 May 2021
[RFC6716] Valin, JM., Vos, K., and T. Terriberry, "Definition of the
Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716,
September 2012, <https://www.rfc-editor.org/info/rfc6716>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10. Informative References
[Address-Sanitizer]
The Clang Team, "ASAN AddressSanitizer website", undated,
<https://clang.llvm.org/docs/AddressSanitizer.html>.
[AVI] Microsoft, "AVI RIFF File Reference", undated,
<https://msdn.microsoft.com/en-us/library/windows/desktop/
dd318189%28v=vs.85%29.aspx>.
[FFV1GO] Buitenhuis, D., "FFV1 Decoder in Go", 2019,
<https://github.com/dwbuiten/go-ffv1>.
[HuffYUV] Rudiak-Gould, B., "HuffYUV", December 2003,
<https://web.archive.org/web/20040402121343/
http://cultact-server.novi.dk/kpo/huffyuv/huffyuv.html>.
[I-D.ietf-cellar-ffv1]
Niedermayer, M., Rice, D., and J. Martinez, "FFV1 Video
Coding Format Version 0, 1, and 3", Work in Progress,
Internet-Draft, draft-ietf-cellar-ffv1-20, 23 February
2021,
<https://tools.ietf.org/html/draft-ietf-cellar-ffv1-20>.
[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.
Niedermayer, et al. Expires 26 November 2021 [Page 55]
Internet-Draft FFV1 May 2021
[ISO.14496-12.2015]
International Organization for Standardization,
"Information technology -- Coding of audio-visual objects
-- Part 12: ISO base media file format", December 2015.
[MediaConch]
MediaArea.net, "MediaConch", 2018,
<https://mediaarea.net/MediaConch>.
[NUT] Niedermayer, M., "NUT Open Container Format", December
2013, <https://ffmpeg.org/~michael/nut.txt>.
[range-coding]
Martin, G. N. N., "Range encoding: an algorithm for
removing redundancy from a digitised message", Proceedings
of the Conference on Video and Data Recording. Institution
of Electronic and Radio Engineers, Hampshire, England,
July 1979.
[REFIMPL] Niedermayer, M., "The reference FFV1 implementation / the
FFV1 codec in FFmpeg", undated, <https://ffmpeg.org>.
[VALGRIND] Valgrind Developers, "Valgrind website", undated,
<https://valgrind.org/>.
[YCbCr] Wikipedia, "YCbCr", undated,
<https://en.wikipedia.org/w/index.php?title=YCbCr>.
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.
Niedermayer, et al. Expires 26 November 2021 [Page 56]
Internet-Draft FFV1 May 2021
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"
== 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.
Appendix C. FFV1 Implementations
This appendix provides references to a few notable implementations of
FFV1.
C.1. FFmpeg FFV1 Codec
This 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:
* 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.
C.2. FFV1 Decoder in Go
An FFV1 decoder was [FFV1GO] written in Go by Derek Buitenhuis during
the work to development this document.
Niedermayer, et al. Expires 26 November 2021 [Page 57]
Internet-Draft FFV1 May 2021
C.3. MediaConch
The developers of the MediaConch project [MediaConch] created an
independent FFV1 decoder as part of that project to validate FFV1
bitstreams. This work led to the discovery of three conflicts
between existing FFV1 implementations and this document without the
added exceptions.
Authors' Addresses
Michael Niedermayer
Email: michael@niedermayer.cc
Dave Rice
Email: dave@dericed.com
Jerome Martinez
Email: jerome@mediaarea.net
Niedermayer, et al. Expires 26 November 2021 [Page 58]