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Versions: 00 01 02

cellar                                                    M. Niedermayer
Internet-Draft                                           January 8, 2017
Intended status: Standards Track
Expires: July 12, 2017

FF Video Codec 1
draft-niedermayer-cellar-ffv1-01

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.

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This Internet-Draft will expire on July 12, 2017.

Copyright (c) 2017 IETF Trust and the persons identified as the

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

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1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
2.  Notation and Conventions  . . . . . . . . . . . . . . . . . .   4
2.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
2.2.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   4
2.2.1.  Arithmetic operators  . . . . . . . . . . . . . . . .   4
2.2.2.  Assignment operators  . . . . . . . . . . . . . . . .   5
2.2.3.  Comparison operators  . . . . . . . . . . . . . . . .   5
2.2.4.  Mathematical functions  . . . . . . . . . . . . . . .   6
2.2.5.  Order of operation precedence . . . . . . . . . . . .   6
2.2.6.  Range . . . . . . . . . . . . . . . . . . . . . . . .   6
2.2.7.  NumBytes  . . . . . . . . . . . . . . . . . . . . . .   6
2.2.8.  Bitstream functions . . . . . . . . . . . . . . . . .   7
3.  General Description . . . . . . . . . . . . . . . . . . . . .   7
3.1.  Border  . . . . . . . . . . . . . . . . . . . . . . . . .   7
3.2.  Median predictor  . . . . . . . . . . . . . . . . . . . .   8
3.3.  Context . . . . . . . . . . . . . . . . . . . . . . . . .   8
3.4.  Quantization  . . . . . . . . . . . . . . . . . . . . . .   9
3.5.  Colorspace  . . . . . . . . . . . . . . . . . . . . . . .   9
3.5.1.  JPEG2000-RCT  . . . . . . . . . . . . . . . . . . . .   9
3.6.  Coding of the sample difference . . . . . . . . . . . . .   9
3.6.1.  Range coding mode . . . . . . . . . . . . . . . . . .  10
3.6.2.  Huffman coding mode . . . . . . . . . . . . . . . . .  13
4.  Bitstream . . . . . . . . . . . . . . . . . . . . . . . . . .  15
4.1.  Configuration Record  . . . . . . . . . . . . . . . . . .  16
4.1.1.  reserved_for_future_use . . . . . . . . . . . . . . .  17
4.1.2.  configuration_record_crc_parity . . . . . . . . . . .  17
4.1.3.  Mapping FFV1 into Containers  . . . . . . . . . . . .  17
4.2.  Frame . . . . . . . . . . . . . . . . . . . . . . . . . .  18
4.3.  Slice . . . . . . . . . . . . . . . . . . . . . . . . . .  18
4.4.  Slice Header  . . . . . . . . . . . . . . . . . . . . . .  18
4.4.1.  slice_x . . . . . . . . . . . . . . . . . . . . . . .  19
4.4.2.  slice_y . . . . . . . . . . . . . . . . . . . . . . .  19
4.4.3.  slice_width . . . . . . . . . . . . . . . . . . . . .  19
4.4.4.  slice_height  . . . . . . . . . . . . . . . . . . . .  19
4.4.5.  quant_table_index_count . . . . . . . . . . . . . . .  19
4.4.6.  quant_table_index . . . . . . . . . . . . . . . . . .  19
4.4.7.  picture_structure . . . . . . . . . . . . . . . . . .  20
4.4.8.  sar_num . . . . . . . . . . . . . . . . . . . . . . .  20
4.4.9.  sar_den . . . . . . . . . . . . . . . . . . . . . . .  20
4.4.10. reset_contexts  . . . . . . . . . . . . . . . . . . .  20
4.4.11. slice_coding_mode . . . . . . . . . . . . . . . . . .  20
4.5.  Slice Content . . . . . . . . . . . . . . . . . . . . . .  20
4.5.1.  primary_color_count . . . . . . . . . . . . . . . . .  21
4.5.2.  plane_pixel_height  . . . . . . . . . . . . . . . . .  21
4.5.3.  slice_pixel_height  . . . . . . . . . . . . . . . . .  21
4.5.4.  slice_pixel_y . . . . . . . . . . . . . . . . . . . .  21

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4.6.  Line  . . . . . . . . . . . . . . . . . . . . . . . . . .  21
4.6.1.  plane_pixel_width . . . . . . . . . . . . . . . . . .  22
4.6.2.  slice_pixel_width . . . . . . . . . . . . . . . . . .  22
4.6.3.  slice_pixel_x . . . . . . . . . . . . . . . . . . . .  22
4.7.  Slice Footer  . . . . . . . . . . . . . . . . . . . . . .  22
4.7.1.  slice_size  . . . . . . . . . . . . . . . . . . . . .  23
4.7.2.  error_status  . . . . . . . . . . . . . . . . . . . .  23
4.7.3.  slice_crc_parity  . . . . . . . . . . . . . . . . . .  23
4.8.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .  23
4.8.1.  version . . . . . . . . . . . . . . . . . . . . . . .  24
4.8.2.  micro_version . . . . . . . . . . . . . . . . . . . .  25
4.8.3.  coder_type  . . . . . . . . . . . . . . . . . . . . .  26
4.8.4.  state_transition_delta  . . . . . . . . . . . . . . .  26
4.8.5.  colorspace_type . . . . . . . . . . . . . . . . . . .  26
4.8.6.  chroma_planes . . . . . . . . . . . . . . . . . . . .  26
4.8.7.  bits_per_raw_sample . . . . . . . . . . . . . . . . .  27
4.8.8.  h_chroma_subsample  . . . . . . . . . . . . . . . . .  27
4.8.9.  v_chroma_subsample  . . . . . . . . . . . . . . . . .  27
4.8.10. alpha_plane . . . . . . . . . . . . . . . . . . . . .  27
4.8.11. num_h_slices  . . . . . . . . . . . . . . . . . . . .  27
4.8.12. num_v_slices  . . . . . . . . . . . . . . . . . . . .  27
4.8.13. quant_table_count . . . . . . . . . . . . . . . . . .  28
4.8.14. states_coded  . . . . . . . . . . . . . . . . . . . .  28
4.8.15. initial_state_delta . . . . . . . . . . . . . . . . .  28
4.8.16. ec  . . . . . . . . . . . . . . . . . . . . . . . . .  28
4.8.17. intra . . . . . . . . . . . . . . . . . . . . . . . .  28
4.9.  Quantization Tables . . . . . . . . . . . . . . . . . . .  29
4.9.1.  quant_tables  . . . . . . . . . . . . . . . . . . . .  30
4.9.2.  context_count . . . . . . . . . . . . . . . . . . . .  30
4.9.3.  Restrictions  . . . . . . . . . . . . . . . . . . . .  30
5.  Security Considerations . . . . . . . . . . . . . . . . . . .  31
6.  Appendixes  . . . . . . . . . . . . . . . . . . . . . . . . .  31
6.1.  Decoder implementation suggestions  . . . . . . . . . . .  32
6.1.1.  Multi-threading support and independence of slices  .  32
7.  Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  32
8.  ToDo  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  32
9.  Copyright . . . . . . . . . . . . . . . . . . . . . . . . . .  33
10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
10.1.  Normative References . . . . . . . . . . . . . . . . . .  33
10.2.  Informative References . . . . . . . . . . . . . . . . .  33
Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

The FFV1 video codec is a simple and efficient lossless intra-frame
only codec.

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<https://raw.github.com/FFmpeg/FFV1/master/ffv1.md>

This document assumes familiarity with mathematical and coding
concepts such as Range coding and YCbCr colorspaces.

2.  Notation and Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

2.1.  Definitions

"ESC": An ESCape symbol to indicate that the symbol to be stored is
too large for normal storage and that an alternate storage method.

"MSB": Most Significant Bit, the bit that can cause the largest
change in magnitude of the symbol.

"RCT": Reversible Color Transform, a near linear, exactly reversible
integer transform that converts between RGB and YCbCr representations
of a sample.

"VLC": Variable Length Code.

"RGB": A reference to the method of storing the value of a sample by
using three numeric values that represent Red, Green, and Blue.

"YCbCr": A reference to the method of storing the value of a sample
by using three numeric values that represent the luminance of the
sample (Y) and the chrominance of the sample (Cb and Cr).

"TBA": To Be Announced.  Used in reference to the development of
future iterations of the FFV1 specification.

2.2.  Conventions

Note: the operators and the order of precedence are the same as used
in the C programming language [ISO.9899.1990].

2.2.1.  Arithmetic operators

"a + b" means a plus b.

"a - b" means a minus b.

"-a" means negation of a.

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"a * b" means a multiplied by b.

"a / b" means a divided by b.

"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.

"a << b" means arithmetic left shift of two's complement integer
representation of a by b binary digits.

2.2.2.  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.

2.2.3.  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".

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"a ? b : c" if a is true, then b, otherwise c.

2.2.4.  Mathematical functions

\lfloor a \rfloor the largest integer less than or equal to a

\lceil a \rceil the smallest integer greater than or equal to a

abs(a) the absolute value of a, i.e. abs(a) = sign(a)*a

log2(a) the base-two logarithm of a

min(a,b) the smallest of two values a and b

2.2.5.  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

2.2.6.  Range

"a...b" means any value starting from a to b, inclusive.

2.2.7.  NumBytes

NumBytes is a non-negative integer that expresses the size in 8-bit
octets of particular FFV1 components such as the Configuration Record
and Frame.  FFV1 relies on its container to store the NumBytes
values, see Section 4.1.3.

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2.2.8.  Bitstream functions

2.2.8.1.  remaining_bits_in_bitstream

"remaining_bits_in_bitstream( )" means the count of remaining bits
after the current position in that bitstream component.  It is
computed from the NumBytes value multiplied by 8 minus the count of

2.2.8.2.  byte_aligned

"byte_aligned( )" is true if "remaining_bits_in_bitstream( NumBytes
)" is a multiple of 8, otherwise false.

3.  General Description

Each frame is split in 1 to 4 planes (Y, Cb, Cr, Alpha).  In the case
of the normal YCbCr colorspace the Y plane is coded first followed by
the Cb and Cr planes, if an Alpha/transparency plane exists, it is
coded last.  In the case of the JPEG2000-RCT colorspace the lines are
interleaved to improve caching efficiency since it is most likely
that the RCT will immediately be converted to RGB during decoding;
the interleaved coding order is also Y, Cb, Cr, Alpha.

Samples within a plane are coded in raster scan order (left->right,
top->bottom).  Each sample is predicted by the median predictor from
samples in the same plane and the difference is stored see
Section 3.6.

3.1.  Border

For the purpose of the predictor and context, samples above the coded
slice are assumed to be 0; samples to the right of the coded slice
are identical to the closest left sample; samples to the left of the
coded slice are identical to the top right sample (if there is one),
otherwise 0.

+---+---+---+---+---+---+---+---+
| 0 | 0 |   | 0 | 0 | 0 |   | 0 |
| 0 | 0 |   | 0 | 0 | 0 |   | 0 |
|   |   |   |   |   |   |   |   |
| 0 | 0 |   | a | b | c |   | c |
| 0 | a |   | d |   | e |   | e |
| 0 | d |   | f | g | h |   | h |
+---+---+---+---+---+---+---+---+

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3.2.  Median predictor

median(left, top, left + top - diag)

left, top, diag are the left, top and left-top samples

Note, this is also used in [ISO.14495-1.1999] and [HuffYUV].

Exception for the media predictor: if colorspace_type == 0 &&
bits_per_raw_sample == 16 && ( coder_type == 1 || coder_type == 2 ),
the following media predictor MUST be used:

median(left16s, top16s, left16s + top16s - diag16s)

with: - left16s = left >= 32768 ? ( left - 65536 ) : left - top16s =
top >= 32768 ? ( top - 65536 ) : top - diag16s = diag >= 32768 ? (
diag - 65536 ) : diag

Background: a two's complement signed 16-bit signed integer was used
for storing pixel 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 is discovered, the only
configuration of all known implementations being impacted is 16-bit
YCbCr color space with Range Coder coder, as other potentially
impacted configurations (e.g. 15/16-bit JPEG2000-RCT color space with
Range Coder coder, or 16-bit any color space with Golomb Rice coder)
were implemented nowhere.  In the meanwhile, 16-bit JPEG2000-RCT
color space 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 media
predictor in the next version of the bitstream.

3.3.  Context

+---+---+---+---+
|   |   | T |   |
+---+---+---+---+
|   |tl | t |tr |
+---+---+---+---+
| L | l | X |   |
+---+---+---+---+

The quantized sample differences L-l, l-tl, tl-t, t-T, t-tr are used
as context:

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context=Q_{0}[l-tl]+\left|Q_{0}\right|(Q_{1}[tl-t]+\left|Q_{1}\right|
(Q_{2}[t-tr]+\left|Q_{2}\right|(Q_{3}[L-l]+\left|Q_{3}\right|Q_{4}[T-
t])))

If the context is smaller than 0 then -context is used and the
difference between the sample and its predicted value is encoded with
a flipped sign.

3.4.  Quantization

There are 5 quantization tables for the 5 sample differences, both
the number of quantization steps and their distribution are stored in
the bitstream.  Each quantization table has exactly 256 entries, and
the 8 least significant bits of the sample difference are used as
index:

Q_{i}[a-b]=Table_{i}[(a-b)\&255]

3.5.  Colorspace

3.5.1.  JPEG2000-RCT

Cb=b-g

Cr=r-g

Y=g+(Cb+Cr)>>2

g=Y-(Cb+Cr)>>2

r=Cr+g

b=Cb+g

[ISO.15444-1.2016]

3.6.  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 RCT), only the
n (or n+1) 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 RCT or
bits_per_raw_sample otherwise:

coder\_input=\left[\left(sample\_difference+2^{bits-
1}\right)\&\left(2^{bits}-1\right)\right]-2^{bits-1}

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3.6.1.  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].

3.6.1.1.  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, which is 128.  The length of the bytestream encoding n binary
symbols is $j_{n}$ bytes.

r_{i}=\left\lfloor \frac{R_{i}S_{i,C_{i}}}{2^{8}}\right\rfloor

\begin{array}{ccccccccc} S_{i+1,C_{i}}=zero\_state_{S_{i,C_{i}}} &
\wedge & l{}_{i}=L_{i} & \wedge & t_{i}=R_{i}-r_{i} & \Longleftarrow
& b_{i}=0 & \Longleftrightarrow & L_{i}<R_{i}-r_{i}\\
S_{i+1,C_{i}}=one\_state_{S_{i,C_{i}}} & \wedge & l_{i}=L_{i}-
R_{i}+r_{i} & \wedge & t_{i}=r_{i} & \Longleftarrow & b_{i}=1 &
\Longleftrightarrow & L_{i}\geq R_{i}-r_{i} \end{array}

\begin{array}{ccc} S_{i+1,k}=S_{i,k} & \Longleftarrow & C_{i}\neq k
\end{array}

\begin{array}{ccccccc} R_{i+1}=2^{8}t_{i} & \wedge &
L_{i+1}=2^{8}l_{i}+B_{j_{i}} & \wedge & j_{i+1}=j_{i}+1 &
\Longleftarrow & t_{i}<2^{8}\\ R_{i+1}=t_{i} & \wedge & L_{i+1}=l_{i}
& \wedge & j_{i+1}=j_{i} & \Longleftarrow & t_{i}\geq2^{8}
\end{array}

R_{0}=65280

L_{0}=2^{8}B_{0}+B_{1}

j_{0}=2

3.6.1.2.  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 which 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)

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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 the
following code, followed by some comments.

function                                                      | 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|
}                                                         |
}                                                             |

3.6.1.3.  Initial values for the context model

At keyframes all Range coder state variables are set to their initial
state.

3.6.1.4.  State transition table

one\_state_{i}=default\_state\_transition_{i}+state\_transition\_delt
a_{i}

zero\_state_{i}=256-one\_state_{256-i}

3.6.1.5.  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,

3.6.1.6.  alternative state transition table

The alternative state transition table has been build using iterative
minimization of frame sizes and generally performs better than the
default.  To use it, the coder_type MUST be set to 2 and the
difference to the default MUST be stored in the parameters.  The
reference implementation of FFV1 in FFmpeg uses this table 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,

3.6.2.  Huffman coding mode

This coding mode uses Golomb Rice codes.  The VLC code is split into
2 parts, the prefix stores the most significant bits, the suffix
stores the k least significant bits or stores the whole number in the
ESC case.  The end of the bitstream (of the frame) is filled with
0-bits until that the bitstream contains a multiple of 8 bits.

3.6.2.1.  Prefix

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+----------------+-------+
| bits           | value |
+----------------+-------+
| 1              | 0     |
| 01             | 1     |
| ...            | ...   |
| 0000 0000 0001 | 11    |
| 0000 0000 0000 | ESC   |
+----------------+-------+

3.6.2.2.  Suffix

+-------+-----------------------------------------------------------+
| non   | the k least significant bits MSB first                    |
| ESC   |                                                           |
| ESC   | the value - 11, in MSB first order, ESC may only be used  |
|       | if the value cannot be coded as non ESC                   |
+-------+-----------------------------------------------------------+

3.6.2.3.  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 |
+-----+-------------------------+-------+

3.6.2.4.  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 is coded.

3.6.2.5.  Run length coding

The run value is encoded in 2 parts, the prefix part stores the more
significant part of the run as well as adjusting the run_index which
determines the number of bits in the less significant part of the
run.  The 2nd 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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function                                                      | 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_bits1()) {                                        |
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 function is also used within [ISO.14495-1.1999].

3.6.2.6.  Level coding

Level coding is identical to the normal difference coding with the
exception that the 0 value is removed as it cannot occur:

if (diff>0) diff--;
encode(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.

4.  Bitstream

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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 3.6.2             |
|   br   |    Range coded Boolean (1-bit) symbol with the method    |
|        |               described in Section 3.6.1.1               |
|   ur   | Range coded unsigned scalar symbol coded with the method |
|        |               described in Section 3.6.1.2               |
|   sr   |  Range coded signed scalar symbol coded with the method  |
|        |               described in Section 3.6.1.2               |
+--------+----------------------------------------------------------+

The same context which is initialized to 128 is used for all fields

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.  Configuration Record

In the case of a 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 frames.  The size of
the Configuration Record, NumBytes, is supplied by the underlying
container.

function                                                      | type
--------------------------------------------------------------|-----
ConfigurationRecord( NumBytes ) {                             |
ConfigurationRecordIsPresent = 1                          |
Parameters( )                                             |
while( remaining_bits_in_bitstream( NumBytes ) > 32 )     |
reserved_for_future_use                               | u(1)
configuration_record_crc_parity                           | u(32)
}                                                             |

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4.1.1.  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.

4.1.2.  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 the standard IEEE CRC polynomial
(0x104C11DB7) with initial value 0.

4.1.3.  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 container
formats:

4.1.3.1.  In AVI File Format

The Configuration Record extends the stream format chunk ("AVI ",
"hdlr", "strl", "strf") with the ConfigurationRecord bitstream.  See

"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.

4.1.3.2.  In ISO/IEC 14496-12 (MP4 File Format)

The Configuration Record extends the sample description box ("moov",
"trak", "mdia", "minf", "stbl", "stsd") with a "glbl" box which
contains the ConfigurationRecord bitstream.  See [ISO.14496-12.2015]

"NumBytes" is defined as the size, in bytes, of the "glbl" box
indicated in the box header minus the size of the box header.

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4.1.3.3.  In NUT File Format

The codec_specific_data element (in "stream_header" packet) contains

"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.  Frame

A frame consists of the keyframe field, parameters (if version <=1),
and a sequence of independent slices.

function                                                      | type
--------------------------------------------------------------|-----
Frame( NumBytes ) {                                           |
keyframe                                                  | br
if (keyframe && !ConfigurationRecordIsPresent             |
Parameters( )                                         |
while ( remaining_bits_in_bitstream( NumBytes ) )         |
Slice( )                                              |
}                                                             |

4.3.  Slice

function                                                      | type
--------------------------------------------------------------|-----
Slice( ) {                                                    |
if (version >= 3)                                         |
SliceContent( )                                           |
if (coder_type == 0)                                      |
while (!byte_aligned())                               |
if (version >= 3)                                         |
SliceFooter( )                                        |
}                                                             |

"padding" specifies a bit without any significance and used only for
byte alignment.  MUST be 0.

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function                                                      | type
--------------------------------------------------------------|-----
slice_x                                                   | ur
slice_y                                                   | ur
slice_width - 1                                           | ur
slice_height - 1                                          | ur
for( i = 0; i < quant_table_index_count; i++ )            |
quant_table_index [ i ]                               | ur
picture_structure                                         | ur
sar_num                                                   | ur
sar_den                                                   | ur
if (version >= 4) {                                       |
reset_contexts                                        | br
slice_coding_mode                                     | ur
}                                                          |
}                                                             |

4.4.1.  slice_x

"slice_x" indicates the x position on the slice raster formed by
num_h_slices.  Inferred to be 0 if not present.

4.4.2.  slice_y

"slice_y" indicates the y position on the slice raster formed by
num_v_slices.  Inferred to be 0 if not present.

4.4.3.  slice_width

"slice_width" indicates the width on the slice raster formed by
num_h_slices.  Inferred to be 1 if not present.

4.4.4.  slice_height

"slice_height" indicates the height on the slice raster formed by
num_v_slices.  Inferred to be 1 if not present.

4.4.5.  quant_table_index_count

"quant_table_index_count" is defined as 1 + ( ( chroma_planes ||
version <= 3 ) ? 1 : 0 ) + ( alpha_plane ? 1 : 0 ).

4.4.6.  quant_table_index

"quant_table_index" indicates the index to select the quantization
table set and the initial states for the slice.  Inferred to be 0 if
not present.

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4.4.7.  picture_structure

"picture_structure" specifies the picture structure.  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 |
+-------+-------------------------+

4.4.8.  sar_num

"sar_num" specifies the sample aspect ratio numerator.  Inferred to
be 0 if not present.  MUST be 0 if sample aspect ratio is unknown.

4.4.9.  sar_den

"sar_den" specifies the sample aspect ratio numerator.  Inferred to
be 0 if not present.  MUST be 0 if sample aspect ratio is unknown.

4.4.10.  reset_contexts

"reset_contexts" indicates if slice contexts must be reset.  Inferred
to be 0 if not present.

4.4.11.  slice_coding_mode

"slice_coding_mode" indicates the slice coding mode.  Inferred to be
0 if not present.

+-------+----------------------------+
| value | slice coding mode          |
+-------+----------------------------+
|   0   | normal Range Coding or VLC |
|   1   | raw PCM                    |
| Other | reserved for future use    |
+-------+----------------------------+

4.5.  Slice Content

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function                                                      | 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 )                                  |
}                                                         |
}                                                             |

4.5.1.  primary_color_count

"primary_color_count" is defined as 1 + ( chroma_planes ? 2 : 0 ) + (
alpha_plane ? 1 : 0 ).

4.5.2.  plane_pixel_height

"plane_pixel_height[ p ]" is the height in pixels of plane p of the
slice.  plane_pixel_height[ 0 ] and plane_pixel_height[ 1 + (
chroma_planes ? 2 : 0 ) ] value is slice_pixel_height if
chroma_planes is set to 1, plane_pixel_height[ 1 ] and
plane_pixel_height[ 2 ] value is $\lceil slice_pixel_height / v_chroma_subsample \rceil$

4.5.3.  slice_pixel_height

"slice_pixel_height" is the height in pixels of the slice.  Its value
is $\lfloor ( slice_y + slice_height ) * slice_pixel_height / num_v_slices \rfloor - slice_pixel_y$

4.5.4.  slice_pixel_y

"slice_pixel_y" is the slice vertical position in pixels.  Its value
is $\lfloor slice_y * frame_pixel_height / num_v_slices \rfloor$

4.6.  Line

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function                                                      | type
--------------------------------------------------------------|-----
Line( p, y ) {                                                |
if (colorspace_type == 0) {                               |
for( x = 0; x < plane_pixel_width[ p ]; x++ )         |
Pixel( p, y, x )                                  |
} else if (colorspace_type == 1) {                        |
for( x = 0; x < slice_pixel_width; x++ )              |
Pixel( p, y, x )                                  |
}                                                         |
}                                                             |

4.6.1.  plane_pixel_width

"plane_pixel_width[ p ]" is the width in pixels of plane p of the
slice.  plane_pixel_width[ 0 ] and plane_pixel_width[ 1 + (
chroma_planes ? 2 : 0 ) ] value is slice_pixel_width if chroma_planes
is set to 1, plane_pixel_width[ 1 ] and plane_pixel_width[ 2 ] value
is $\lceil slice_pixel_width / v_chroma_subsample \rceil$

4.6.2.  slice_pixel_width

"slice_pixel_width" is the width in pixels of the slice.  Its value
is $\lfloor ( slice_x + slice_width ) * slice_pixel_width / num_h_slices \rfloor - slice_pixel_x$

4.6.3.  slice_pixel_x

"slice_pixel_x" is the slice horizontal position in pixels.  Its
value is $\lfloor slice_x * frame_pixel_width / num_h_slices \rfloor$

4.7.  Slice Footer

Note: slice footer is always byte aligned.

function                                                      | type
--------------------------------------------------------------|-----
SliceFooter( ) {                                              |
slice_size                                                | u(24)
if (ec) {                                                 |
error_status                                          | u(8)
slice_crc_parity                                      | u(32)
}                                                         |
}                                                             |

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4.7.1.  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 this way parallel decoding as well as
error resilience.

4.7.2.  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              |
+-------+--------------------------------------+

4.7.3.  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.

4.8.  Parameters

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function                                                      | 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
alpha_plane                                               | br
if (version >= 3) {                                       |
num_h_slices - 1                                      | ur
num_v_slices - 1                                      | ur
quant_table_count                                     | ur
}                                                         |
for( i = 0; i < quant_table_count; i++ )                  |
QuantizationTable( i )                                |
if (version >= 3) {                                       |
for( i = 0; i < quant_table_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
}                                                         |
}                                                             |

4.8.1.  version

"version" specifies the version of the bitstream.  Each version is
incompatible with others versions: decoders SHOULD reject a file due
to unknown version.  Decoders SHOULD reject a file with version =< 1
&& ConfigurationRecordIsPresent == 1.  Decoders SHOULD reject a file
with version >= 3 && ConfigurationRecordIsPresent == 0.

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+-------+-------------------------+
| value | version                 |
+-------+-------------------------+
| 0     | FFV1 version 0          |
| 1     | FFV1 version 1          |
| 2     | reserved*               |
| 3     | FFV1 version 3          |
| Other | reserved for future use |
+-------+-------------------------+

* Version 2 was never enabled in the encoder thus version 2 files
SHOULD NOT exist, and this document does not describe them to keep
the text simpler.

4.8.2.  micro_version

"micro_version" specifies the micro-version of the 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 a file due to an
unknown micro-version equal or above the micro-version considered as
stable.

Meaning of micro_version for version 3:

+-------+-------------------------+
| value | micro_version           |
+-------+-------------------------+
| 0...3 | reserved*               |
|   4   | first stable variant    |
| Other | reserved for future use |
+-------+-------------------------+

* were development versions which 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 version value is to be announced in the future):

+---------+-------------------------+
|  value  | micro_version           |
+---------+-------------------------+
| 0...TBA | reserved*               |
|   TBA   | first stable variant    |
|  Other  | reserved for future use |
+---------+-------------------------+

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* were development versions which may be incompatible with the stable
variants.

4.8.3.  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                         |
+-------+-------------------------------------------------+

4.8.4.  state_transition_delta

"state_transition_delta" specifies the Range coder custom state
transition table.  If state_transition_delta is not present in the
bitstream, all Range coder custom state transition table elements are
assumed to be 0.

4.8.5.  colorspace_type

"colorspace_type" specifies the color space.

+-------+-------------------------+
| value | color space used        |
+-------+-------------------------+
|   0   | YCbCr                   |
|   1   | JPEG2000-RCT            |
| Other | reserved for future use |
+-------+-------------------------+

4.8.6.  chroma_planes

"chroma_planes" indicates if chroma (color) planes are present.

+-------+-------------------------------+
| value | color space used              |
+-------+-------------------------------+
|   0   | chroma planes are not present |
|   1   | chroma planes are present     |
+-------+-------------------------------+

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4.8.7.  bits_per_raw_sample

"bits_per_raw_sample" indicates the number of bits for each luma and
chroma sample.  Inferred to be 8 if not present.

+-------+-------------------------------------------------+
| value | bits for each luma and chroma sample            |
+-------+-------------------------------------------------+
|   0   | reserved*                                       |
| Other | the actual bits for each luma and chroma sample |
+-------+-------------------------------------------------+

* Encoders MUST NOT store bits_per_raw_sample = 0 Decoders SHOULD
accept and interpret bits_per_raw_sample = 0 as 8.

4.8.8.  h_chroma_subsample

"h_chroma_subsample" indicates the subsample factor between luma and
chroma width ($chroma_width=2^{-log2_h_chroma_subsample}luma_width$)

4.8.9.  v_chroma_subsample

"v_chroma_subsample" indicates the subsample factor between luma and
chroma height
($chroma_height=2^{-log2_v_chroma_subsample}luma_height$)

4.8.10.  alpha_plane

alpha_plane
indicates if a transparency plane is present.

+-------+-----------------------------------+
| value | color space used                  |
+-------+-----------------------------------+
|   0   | transparency plane is not present |
|   1   | transparency plane is present     |
+-------+-----------------------------------+

4.8.11.  num_h_slices

"num_h_slices" indicates the number of horizontal elements of the
slice raster.  Inferred to be 1 if not present.

4.8.12.  num_v_slices

"num_v_slices" indicates the number of vertical elements of the slice
raster.  Inferred to be 1 if not present.

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4.8.13.  quant_table_count

"quant_table_count" indicates the number of quantization table sets.
Inferred to be 1 if not present.

4.8.14.  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                                |
+-------+-----------------------------------------------------------+

4.8.15.  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 initial_state[ i ][ j ][ k ] =
( pred + initial_state_delta[ i ][ j ][ k ] ) & 255

4.8.16.  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                    |
+-------+--------------------------------------------+

4.8.17.  intra

"intra" indicates the relationship between frames.  Inferred to be 0
if not present.

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+-------+-----------------------------------------------------------+
| value | relationship                                              |
+-------+-----------------------------------------------------------+
|   0   | frames are independent or dependent (keyframes and non    |
|       | keyframes)                                                |
|   1   | frames are independent (keyframes only)                   |
| Other | reserved for future use                                   |
+-------+-----------------------------------------------------------+

4.9.  Quantization Tables

The quantization tables are stored by storing the number of equal
entries -1 of the first half of the table using the method described
in Section 3.6.1.2.  The second half doesn't need to be stored as it
is identical to the first with flipped sign.

example:

Table: 0 0 1 1 1 1 2 2-2-2-2-1-1-1-1 0

Stored values: 1, 3, 1

function                                                      | type
--------------------------------------------------------------|-----
QuantizationTable( i ) {                                      |
scale = 1                                                 |
for( j = 0; j < MAX_CONTEXT_INPUTS; j++ ) {               |
QuantizationTablePerContext( i, j, scale )            |
scale *= 2 * len_count[ i ][ j ] - 1                  |
}                                                         |
context_count[ i ] = ( scale + 1 ) / 2                    |
}                                                             |

MAX_CONTEXT_INPUTS is 5.

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function                                                      | type
--------------------------------------------------------------|-----
QuantizationTablePerContext(i, j, scale) {                    |
v = 0                                                     |
for( k = 0; k < 128; ) {                                  |
len - 1                                               | sr
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" indicates the quantification table values.

4.9.2.  context_count

"context_count" indicates the count of contexts.

4.9.3.  Restrictions

To ensure that fast multithreaded decoding is possible, starting
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, except if reset_contexts is 1.

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5.  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
its allocated memory or to take an excessive amount of resources to
decode.  Although problems in encoders are typically rarer, the same
applies to the encoder.  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 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:

o  Sending the decoder valid packets generated by the reference
encoder and verifying that the decoder's output matches the
encoders input.

o  Sending the decoder packets generated by the reference encoder and
then subjected to random corruption.

o  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
invalid memory regions as well as the use of uninitialized memory.
There were no errors reported on any of the tested conditions.

6.  Appendixes

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6.1.  Decoder implementation suggestions

6.1.1.  Multi-threading support and independence of slices

The 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 corrupted
frame (frame size unknown, slice_size of slices not coherent...) or
if there is no possibility of seek into the stream.

Architecture overview of slices in a frame:

+-----------------------------------------------------------------+
| first slice content                                             |
| first slice footer                                              |
| --------------------------------------------------------------- |
| second slice content                                            |
| second slice footer                                             |
| --------------------------------------------------------------- |
| ...                                                             |
| --------------------------------------------------------------- |
| last slice content                                              |
| last slice footer                                               |
+-----------------------------------------------------------------+

7.  Changelog

See <https://github.com/FFmpeg/FFV1/commits/master>

8.  ToDo

o  mean,k estimation for the Golomb Rice codes

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Copyright 2003-2013 Michael Niedermayer <michaelni@gmx.at> This text
can be used under the GNU Free Documentation License or GNU General

10.  References

10.1.  Normative References

[ISO.15444-1.2016]
International Organization for Standardization,
"Information technology -- JPEG 2000 image coding system:
Core coding system", October 2016.

[ISO.9899.1990]
International Organization for Standardization,
"Programming languages - C", ISO Standard 9899, 1990.

[RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

10.2.  Informative References

The Clang Team, "ASAN AddressSanitizer website", undated,

[AVI]      Microsoft, "AVI RIFF File Reference", undated,
<https://msdn.microsoft.com/en-us/library/windows/desktop/
dd318189%28v=vs.85%29.aspx>.

[HuffYUV]  Rudiak-Gould, B., "HuffYUV", December 2003,
<https://web.archive.org/web/20040402121343/
http://cultact-server.novi.dk/kpo/huffyuv/huffyuv.html>.

[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.

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[ISO.14496-12.2015]
International Organization for Standardization,
"Information technology -- Coding of audio-visual objects
-- Part 12: ISO base media file format", December 2015.

[NUT]      Niedermayer, M., "NUT Open Container Format", December
2013, <https://ffmpeg.org/~michael/nut.txt>.

[range-coding]
Nigel, G. and N. Martin, "Range encoding: an algorithm for
removing redundancy from a digitised message.", Proc.
Institution of Electronic and Radio Engineers
International Conference on Video and Data Recording ,
July 1979.

[REFIMPL]  Niedermayer, M., "The reference FFV1 implementation / the
FFV1 codec in FFmpeg", undated, <https://ffmpeg.org>.

[RFC4732]  Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
<http://www.rfc-editor.org/info/rfc4732>.

[RFC6716]  Valin, JM., Vos, K., and T. Terriberry, "Definition of the
Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716,
September 2012, <http://www.rfc-editor.org/info/rfc6716>.

[VALGRIND]
Valgrind Developers, "Valgrind website", undated,
<https://valgrind.org/>.

Michael Niedermayer

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