cellar M. Niedermayer Internet-Draft Intended status: Informational D. Rice Expires: 30 October 2020 J. Martinez 28 April 2020 FFV1 Video Coding Format Version 0, 1, and 3 draft-ietf-cellar-ffv1-13 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 30 October 2020. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. Niedermayer, et al. Expires 30 October 2020 [Page 1] Internet-Draft FFV1 April 2020 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 . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1. Pseudo-code . . . . . . . . . . . . . . . . . . . . . 6 2.2.2. Arithmetic Operators . . . . . . . . . . . . . . . . 6 2.2.3. Assignment Operators . . . . . . . . . . . . . . . . 6 2.2.4. Comparison Operators . . . . . . . . . . . . . . . . 7 2.2.5. Mathematical Functions . . . . . . . . . . . . . . . 7 2.2.6. Order of Operation Precedence . . . . . . . . . . . . 8 2.2.7. Range . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.8. NumBytes . . . . . . . . . . . . . . . . . . . . . . 8 2.2.9. Bitstream Functions . . . . . . . . . . . . . . . . . 8 3. Sample Coding . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1. Border . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Samples . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.3. Median Predictor . . . . . . . . . . . . . . . . . . . . 10 3.4. Context . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.5. Quantization Table Sets . . . . . . . . . . . . . . . . . 12 3.6. Quantization Table Set Indexes . . . . . . . . . . . . . 12 3.7. Color spaces . . . . . . . . . . . . . . . . . . . . . . 12 3.7.1. YCbCr . . . . . . . . . . . . . . . . . . . . . . . . 13 3.7.2. RGB . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.8. Coding of the Sample Difference . . . . . . . . . . . . . 15 3.8.1. Range Coding Mode . . . . . . . . . . . . . . . . . . 15 3.8.2. Golomb Rice Mode . . . . . . . . . . . . . . . . . . 20 4. Bitstream . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.1. Parameters . . . . . . . . . . . . . . . . . . . . . . . 26 4.1.1. version . . . . . . . . . . . . . . . . . . . . . . . 28 4.1.2. micro_version . . . . . . . . . . . . . . . . . . . . 28 4.1.3. coder_type . . . . . . . . . . . . . . . . . . . . . 29 4.1.4. state_transition_delta . . . . . . . . . . . . . . . 29 4.1.5. colorspace_type . . . . . . . . . . . . . . . . . . . 30 4.1.6. chroma_planes . . . . . . . . . . . . . . . . . . . . 30 4.1.7. bits_per_raw_sample . . . . . . . . . . . . . . . . . 31 4.1.8. log2_h_chroma_subsample . . . . . . . . . . . . . . . 31 4.1.9. log2_v_chroma_subsample . . . . . . . . . . . . . . . 31 Niedermayer, et al. Expires 30 October 2020 [Page 2] Internet-Draft FFV1 April 2020 4.1.10. "extra\_plane" . . . . . . . . . . . . . . . . . . . 31 4.1.11. num_h_slices . . . . . . . . . . . . . . . . . . . . 31 4.1.12. num_v_slices . . . . . . . . . . . . . . . . . . . . 32 4.1.13. quant_table_set_count . . . . . . . . . . . . . . . . 32 4.1.14. states_coded . . . . . . . . . . . . . . . . . . . . 32 4.1.15. initial_state_delta . . . . . . . . . . . . . . . . . 32 4.1.16. ec . . . . . . . . . . . . . . . . . . . . . . . . . 33 4.1.17. intra . . . . . . . . . . . . . . . . . . . . . . . . 33 4.2. Configuration Record . . . . . . . . . . . . . . . . . . 33 4.2.1. reserved_for_future_use . . . . . . . . . . . . . . . 34 4.2.2. configuration_record_crc_parity . . . . . . . . . . . 34 4.2.3. Mapping FFV1 into Containers . . . . . . . . . . . . 34 4.3. Frame . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.4. Slice . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.5. Slice Header . . . . . . . . . . . . . . . . . . . . . . 38 4.5.1. slice_x . . . . . . . . . . . . . . . . . . . . . . . 38 4.5.2. slice_y . . . . . . . . . . . . . . . . . . . . . . . 38 4.5.3. slice_width . . . . . . . . . . . . . . . . . . . . . 38 4.5.4. slice_height . . . . . . . . . . . . . . . . . . . . 39 4.5.5. quant_table_set_index_count . . . . . . . . . . . . . 39 4.5.6. quant_table_set_index . . . . . . . . . . . . . . . . 39 4.5.7. picture_structure . . . . . . . . . . . . . . . . . . 39 4.5.8. sar_num . . . . . . . . . . . . . . . . . . . . . . . 39 4.5.9. sar_den . . . . . . . . . . . . . . . . . . . . . . . 40 4.6. Slice Content . . . . . . . . . . . . . . . . . . . . . . 40 4.6.1. primary_color_count . . . . . . . . . . . . . . . . . 41 4.6.2. plane_pixel_height . . . . . . . . . . . . . . . . . 41 4.6.3. slice_pixel_height . . . . . . . . . . . . . . . . . 41 4.6.4. slice_pixel_y . . . . . . . . . . . . . . . . . . . . 41 4.7. Line . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.7.1. plane_pixel_width . . . . . . . . . . . . . . . . . . 42 4.7.2. slice_pixel_width . . . . . . . . . . . . . . . . . . 42 4.7.3. slice_pixel_x . . . . . . . . . . . . . . . . . . . . 42 4.7.4. sample_difference . . . . . . . . . . . . . . . . . . 42 4.8. Slice Footer . . . . . . . . . . . . . . . . . . . . . . 43 4.8.1. slice_size . . . . . . . . . . . . . . . . . . . . . 43 4.8.2. error_status . . . . . . . . . . . . . . . . . . . . 43 4.8.3. slice_crc_parity . . . . . . . . . . . . . . . . . . 43 4.9. Quantization Table Set . . . . . . . . . . . . . . . . . 44 4.9.1. quant_tables . . . . . . . . . . . . . . . . . . . . 45 4.9.2. context_count . . . . . . . . . . . . . . . . . . . . 45 5. Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 45 6. Security Considerations . . . . . . . . . . . . . . . . . . . 46 7. Media Type Definition . . . . . . . . . . . . . . . . . . . . 47 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48 9. Appendix A: Multi-theaded decoder implementation suggestions . . . . . . . . . . . . . . . . . . . . . . . 48 10. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Niedermayer, et al. Expires 30 October 2020 [Page 3] Internet-Draft FFV1 April 2020 11. Normative References . . . . . . . . . . . . . . . . . . . . 49 12. Informative References . . . . . . . . . . . . . . . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51 1. Introduction This document describes FFV1, a lossless video encoding format. The design of FFV1 considers the storage of image characteristics, data fixity, and the optimized use of encoding time and storage requirements. FFV1 is designed to support a wide range of lossless video applications such as long-term audiovisual preservation, scientific imaging, screen recording, and other video encoding scenarios that seek to avoid the generational loss of lossy video encodings. This document defines version 0, 1 and 3 of FFV1. The distinctions of the versions are provided throughout the document, but in summary: * Version 0 of FFV1 was the original implementation of FFV1 and has been in non-experimental use since April 14, 2006 [FFV1_V0]. * Version 1 of FFV1 adds support of more video bit depths and has been in use since April 24, 2009 [FFV1_V1]. * Version 2 of FFV1 only existed in experimental form and is not described by this document, but is available as a LyX file at https://github.com/FFmpeg/FFV1/ blob/8ad772b6d61c3dd8b0171979a2cd9f11924d5532/ffv1.lyx (https://github.com/FFmpeg/FFV1/ blob/8ad772b6d61c3dd8b0171979a2cd9f11924d5532/ffv1.lyx). * Version 3 of FFV1 adds several features such as increased description of the characteristics of the encoding images and embedded CRC data to support fixity verification of the encoding. Version 3 has been in non-experimental use since August 17, 2013 [FFV1_V3]. This document assumes familiarity with mathematical and coding concepts such as Range coding [range-coding] and YCbCr color spaces [YCbCr]. 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 30 October 2020 [Page 4] Internet-Draft FFV1 April 2020 2.1. Definitions "Container": Format that encapsulates "Frames" (see Section 4.3) and (when required) a "Configuration Record" into a bitstream. "Sample": The smallest addressable representation of a color component or a luma component in a "Frame". Examples of "Sample" are Luma, Blue Chrominance, Red Chrominance, Transparency, Red, Green, and Blue. "Plane": A discrete component of a static image comprised of "Samples" that represent a specific quantification of "Samples" of that image. "Pixel": The smallest addressable representation of a color in a "Frame". It is composed of 1 or more "Samples". "ESC": An ESCape symbol to indicate that the symbol to be stored is too large for normal storage and that an alternate storage method is used. "MSB": Most Significant Bit, the bit that can cause the largest change in magnitude of the symbol. "RCT": Reversible Color Transform, a near linear, exactly reversible integer transform that converts between RGB and YCbCr representations of a "Pixel". "VLC": Variable Length Code, a code that maps source symbols to a variable number of bits. "RGB": A reference to the method of storing the value of a "Pixel" by using three numeric values that represent Red, Green, and Blue. "YCbCr": A reference to the method of storing the value of a "Pixel" by using three numeric values that represent the luma of the "Pixel" (Y) and the chrominance of the "Pixel" (Cb and Cr). YCbCr word is used for historical reasons and currently references any color space relying on 1 luma "Sample" and 2 chrominance "Samples", e.g. YCbCr, YCgCo or ICtCp. The exact meaning of the three numeric values is unspecified. "TBA": To Be Announced. Used in reference to the development of future iterations of the FFV1 specification. Niedermayer, et al. Expires 30 October 2020 [Page 5] Internet-Draft FFV1 April 2020 2.2. Conventions 2.2.1. Pseudo-code The FFV1 bitstream is described in this document using pseudo-code. Note that the pseudo-code is used for clarity in order to illustrate the structure of FFV1 and not intended to specify any particular implementation. The pseudo-code used is based upon the C programming language [ISO.9899.1990] and uses its "if/else", "while" and "for" keywords as well as functions defined within this document. 2.2.2. Arithmetic Operators Note: the operators and the order of precedence are the same as used in the C programming language [ISO.9899.2018]. With the exception of ">>" (removal of implementation defined behavior) and "^" (power instead of XOR) operators which are re-defined within this section. "a + b" means a plus b. "a - b" means a minus b. "-a" means negation of a. "a * b" means a multiplied by b. "a / b" means a divided by b. "a ^ b" means a raised to the b-th power. "a & b" means bit-wise "and" of a and b. "a | b" means bit-wise "or" of a and b. "a >> b" means arithmetic right shift of two's complement integer representation of a by b binary digits. This is equivalent to, b times dividing a by 2 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. Niedermayer, et al. Expires 30 October 2020 [Page 6] Internet-Draft FFV1 April 2020 "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" means a is greater than b. "a >= b" means a is greater than or equal to b. "a < b" means a is less than b. "a <= b" means a is less than or equal b. "a == b" means a is equal to b. "a != b" means a is not equal to b. "a && b" means Boolean logical "and" of a and b. "a || b" means Boolean logical "or" of a and b. "!a" means Boolean logical "not" of a. "a ? b : c" if a is true, then b, otherwise c. 2.2.5. Mathematical Functions floor(a) the largest integer less than or equal to a ceil(a) the smallest integer greater than or equal to a sign(a) extracts the sign of a number, i.e. if a < 0 then -1, else if a > 0 then 1, else 0 abs(a) 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 max(a,b) the largest of two values a and b median(a,b,c) 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) Niedermayer, et al. Expires 30 October 2020 [Page 7] Internet-Draft FFV1 April 2020 A <== B B implies A A <==> B A <== B , B <== A 2.2.6. Order of Operation Precedence When order of precedence is not indicated explicitly by use of parentheses, operations are evaluated in the following order (from top to bottom, operations of same precedence being evaluated from left to right). This order of operations is based on the order of operations used in Standard C. a++, a-- !a, -a a ^ b a * b, a / b, a % b a + b, a - b a << b, a >> b a < b, a <= b, a > b, a >= b a == b, a != b a & b a | b a && b a || b a ? b : c a = b, a += b, a -= b, a *= b 2.2.7. Range "a...b" means any value starting from a to b, inclusive. 2.2.8. NumBytes "NumBytes" is a non-negative integer that expresses the size in 8-bit octets of a particular FFV1 "Configuration Record" or "Frame". FFV1 relies on its "Container" to store the "NumBytes" values; see Section 4.2.3. 2.2.9. Bitstream Functions 2.2.9.1. remaining_bits_in_bitstream "remaining_bits_in_bitstream( )" means the count of remaining bits after the pointer in that "Configuration Record" or "Frame". It is computed from the "NumBytes" value multiplied by 8 minus the count of bits of that "Configuration Record" or "Frame" already read by the bitstream parser. Niedermayer, et al. Expires 30 October 2020 [Page 8] Internet-Draft FFV1 April 2020 2.2.9.2. remaining_symbols_in_syntax "remaining_symbols_in_syntax( )" is true as long as the RangeCoder has not consumed all the given input bytes. 2.2.9.3. byte_aligned "byte_aligned( )" is true if "remaining_bits_in_bitstream( NumBytes )" is a multiple of 8, otherwise false. 2.2.9.4. get_bits "get_bits( i )" is the action to read the next "i" bits in the bitstream, from most significant bit to least significant bit, and to return the corresponding value. The pointer is increased by "i". 3. Sample Coding For each "Slice" (as described in Section 4.4) of a "Frame", the "Planes", "Lines", and "Samples" are coded in an order determined by the "Color Space" (see Section 3.7). Each "Sample" is predicted by the median predictor as described in Section 3.3 from other "Samples" within the same "Plane" and the difference is stored using the method described in Section 3.8. 3.1. Border A border is assumed for each coded "Slice" for the purpose of the median predictor and context according to the following rules: * one column of "Samples" to the left of the coded slice is assumed as identical to the "Samples" of the leftmost column of the coded slice shifted down by one row. The value of the topmost "Sample" of the column of "Samples" to the left of the coded slice is assumed to be "0" * one column of "Samples" to the right of the coded slice is assumed as identical to the "Samples" of the rightmost column of the coded slice * an additional column of "Samples" to the left of the coded slice and two rows of "Samples" above the coded slice are assumed to be "0" Figure 1 depicts a slice of 9 "Samples" "a,b,c,d,e,f,g,h,i" in a 3x3 arrangement along with its assumed border. Niedermayer, et al. Expires 30 October 2020 [Page 9] Internet-Draft FFV1 April 2020 +---+---+---+---+---+---+---+---+ | 0 | 0 | | 0 | 0 | 0 | | 0 | +---+---+---+---+---+---+---+---+ | 0 | 0 | | 0 | 0 | 0 | | 0 | +---+---+---+---+---+---+---+---+ | | | | | | | | | +---+---+---+---+---+---+---+---+ | 0 | 0 | | a | b | c | | c | +---+---+---+---+---+---+---+---+ | 0 | a | | d | e | f | | f | +---+---+---+---+---+---+---+---+ | 0 | d | | g | h | i | | i | +---+---+---+---+---+---+---+---+ Figure 1: A depiction of FFV1's assumed border for a set example Samples. 3.2. Samples Relative to any "Sample" "X", six other relatively positioned "Samples" from the coded "Samples" and presumed border are identified according to the labels used in Figure 2. The labels for these relatively positioned "Samples" are used within the median predictor and context. +---+---+---+---+ | | | T | | +---+---+---+---+ | |tl | t |tr | +---+---+---+---+ | L | l | X | | +---+---+---+---+ Figure 2: A depiction of how relatively positions Samples are references within this document. The labels for these relative "Samples" are made of the first letters of the words Top, Left and Right. 3.3. Median Predictor The prediction for any "Sample" value at position "X" may be computed based upon the relative neighboring values of "l", "t", and "tl" via this equation: "median(l, t, l + t - tl)". Niedermayer, et al. Expires 30 October 2020 [Page 10] Internet-Draft FFV1 April 2020 Note, this prediction template is also used in [ISO.14495-1.1999] and [HuffYUV]. Exception for the median predictor: if "colorspace_type == 0 && bits_per_raw_sample == 16 && ( coder_type == 1 || coder_type == 2 )", the following median predictor MUST be used: "median(left16s, top16s, left16s + top16s - diag16s)" where: left16s = l >= 32768 ? ( l - 65536 ) : l top16s = t >= 32768 ? ( t - 65536 ) : t diag16s = tl >= 32768 ? ( tl - 65536 ) : tl Background: a two's complement signed 16-bit signed integer was used for storing "Sample" values in all known implementations of FFV1 bitstream. So in some circumstances, the most significant bit was wrongly interpreted (used as a sign bit instead of the 16th bit of an unsigned integer). Note that when the issue is discovered, the only configuration of all known implementations being impacted is 16-bit YCbCr with no Pixel transformation with Range Coder coder, as other potentially impacted configurations (e.g. 15/16-bit JPEG2000-RCT with Range Coder coder, or 16-bit content with Golomb Rice coder) were implemented nowhere [ISO.15444-1.2016]. In the meanwhile, 16-bit JPEG2000-RCT with Range Coder coder was implemented without this issue in one implementation and validated by one conformance checker. It is expected (to be confirmed) to remove this exception for the median predictor in the next version of the FFV1 bitstream. 3.4. Context Relative to any "Sample" "X", the Quantized Sample Differences "L-l", "l-tl", "tl-t", "T-t", and "t-tr" are used as context: context = Q_{0}[l - tl] + Q_{1}[tl - t] + Q_{2}[t - tr] + Q_{3}[L - l] + Q_{4}[T - t] Figure 3 If "context >= 0" then "context" is used and the difference between the "Sample" and its predicted value is encoded as is, else "-context" is used and the difference between the "Sample" and its predicted value is encoded with a flipped sign. Niedermayer, et al. Expires 30 October 2020 [Page 11] Internet-Draft FFV1 April 2020 3.5. Quantization Table Sets The FFV1 bitstream contains 1 or more Quantization Table Sets. Each Quantization Table Set contains exactly 5 Quantization Tables with each Quantization Table corresponding to 1 of the 5 Quantized Sample Differences. For each Quantization Table, both the number of quantization steps and their distribution are stored in the FFV1 bitstream; each Quantization Table has exactly 256 entries, and the 8 least significant bits of the Quantized Sample Difference are used as index: Q_{j}[k] = quant_tables[i][j][k&255] Figure 4 In this formula, "i" is the Quantization Table Set index, "j" is the Quantized Table index, "k" the Quantized Sample Difference. 3.6. Quantization Table Set Indexes For each "Plane" of each slice, a Quantization Table Set is selected from an index: * For Y "Plane", "quant_table_set_index[ 0 ]" index is used * For Cb and Cr "Planes", "quant_table_set_index[ 1 ]" index is used * For extra "Plane", "quant_table_set_index[ (version <= 3 || chroma_planes) ? 2 : 1 ]" index is used Background: in first implementations of FFV1 bitstream, the index for Cb and Cr "Planes" was stored even if it is not used (chroma_planes set to 0), this index is kept for version <= 3 in order to keep compatibility with FFV1 bitstreams in the wild. 3.7. Color spaces FFV1 supports several color spaces. The count of allowed coded planes and the meaning of the extra "Plane" are determined by the selected color space. The FFV1 bitstream interleaves data in an order determined by the color space. In YCbCr for each "Plane", each "Line" is coded from top to bottom and for each "Line", each "Sample" is coded from left to right. In JPEG2000-RCT for each "Line" from top to bottom, each "Plane" is coded and for each "Plane", each "Sample" is encoded from left to right. Niedermayer, et al. Expires 30 October 2020 [Page 12] Internet-Draft FFV1 April 2020 3.7.1. YCbCr This color space allows 1 to 4 "Planes". The Cb and Cr "Planes" are optional, but if used then MUST be used together. Omitting the Cb and Cr "Planes" codes the frames in grayscale without color data. An optional transparency "Plane" can be used to code transparency data. An FFV1 "Frame" using YCbCr MUST use one of the following arrangements: * Y * Y, Transparency * Y, Cb, Cr * Y, Cb, Cr, Transparency The Y "Plane" MUST be coded first. If the Cb and Cr "Planes" are used then they MUST be coded after the Y "Plane". If a transparency "Plane" is used, then it MUST be coded last. 3.7.2. RGB This color space allows 3 or 4 "Planes". An optional transparency "Plane" can be used to code transparency data. JPEG2000-RCT is a Reversible Color Transform that codes RGB (red, green, blue) "Planes" losslessly in a modified YCbCr color space [ISO.15444-1.2016]. Reversible Pixel transformations between YCbCr and RGB use the following formulae. Cb=b-g Cr=r-g Y=g+(Cb+Cr)>>2 g=Y-(Cb+Cr)>>2 r=Cr+g b=Cb+g Figure 5 Niedermayer, et al. Expires 30 October 2020 [Page 13] Internet-Draft FFV1 April 2020 Exception for the JPEG2000-RCT conversion: if "bits_per_raw_sample" is between 9 and 15 inclusive and "extra_plane" is 0, the following formulae for reversible conversions between YCbCr and RGB MUST be used instead of the ones above: Cb=g-b Cr=r-b Y=b+(Cb+Cr)>>2 b=Y-(Cb+Cr)>>2 r=Cr+b g=Cb+b Figure 6 Background: At the time of this writing, in all known implementations of FFV1 bitstream, when "bits_per_raw_sample" was between 9 and 15 inclusive and "extra_plane" is 0, GBR "Planes" were used as BGR "Planes" during both encoding and decoding. In the meanwhile, 16-bit JPEG2000-RCT was implemented without this issue in one implementation and validated by one conformance checker. Methods to address this exception for the transform are under consideration for the next version of the FFV1 bitstream. Cb and Cr are positively offseted by "1 << bits_per_raw_sample" after the conversion from RGB to the modified YCbCr and are negatively offseted by the same value before the conversion from the modified YCbCr to RGB, in order to have only non-negative values after the conversion. When FFV1 uses the JPEG2000-RCT, the horizontal "Lines" are interleaved to improve caching efficiency since it is most likely that the JPEG2000-RCT will immediately be converted to RGB during decoding. The interleaved coding order is also Y, then Cb, then Cr, and then if used transparency. As an example, a "Frame" that is two "Pixels" wide and two "Pixels" high, could comprise the following structure: +------------------------+------------------------+ | Pixel(1,1) | Pixel(2,1) | | Y(1,1) Cb(1,1) Cr(1,1) | Y(2,1) Cb(2,1) Cr(2,1) | +------------------------+------------------------+ | Pixel(1,2) | Pixel(2,2) | | Y(1,2) Cb(1,2) Cr(1,2) | Y(2,2) Cb(2,2) Cr(2,2) | +------------------------+------------------------+ Niedermayer, et al. Expires 30 October 2020 [Page 14] Internet-Draft FFV1 April 2020 In JPEG2000-RCT, the coding order would be left to right and then top to bottom, with values interleaved by "Lines" and stored in this order: Y(1,1) Y(2,1) Cb(1,1) Cb(2,1) Cr(1,1) Cr(2,1) Y(1,2) Y(2,2) Cb(1,2) Cb(2,2) Cr(1,2) Cr(2,2) 3.8. Coding of the Sample Difference Instead of coding the n+1 bits of the Sample Difference with Huffman or Range coding (or n+2 bits, in the case of JPEG2000-RCT), only the n (or n+1, in the case of JPEG2000-RCT) least significant bits are used, since this is sufficient to recover the original "Sample". In the equation below, the term "bits" represents "bits_per_raw_sample + 1" for JPEG2000-RCT or "bits_per_raw_sample" otherwise: coder_input = [(sample_difference + 2^(bits-1)) & (2^bits - 1)] - 2^(bits-1) Figure 7 3.8.1. Range Coding Mode Early experimental versions of FFV1 used the CABAC Arithmetic coder from H.264 as defined in [ISO.14496-10.2014] but due to the uncertain patent/royalty situation, as well as its slightly worse performance, CABAC was replaced by a Range coder based on an algorithm defined by G. Nigel and N. Martin in 1979 [range-coding]. 3.8.1.1. Range Binary Values To encode binary digits efficiently a Range coder is used. "C(i)" is the i-th Context. "B(i)" is the i-th byte of the bytestream. "b(i)" is the i-th Range coded binary value, "S(0,i)" is the i-th initial state. The length of the bytestream encoding n binary symbols is "j(n)" bytes. r_{i} = floor( ( R_{i} * S_{i,C_{i}} ) / 2^8 ) Figure 8 Niedermayer, et al. Expires 30 October 2020 [Page 15] Internet-Draft FFV1 April 2020 S_{i+1,C_{i}} = zero_state_{S_{i,C_{i}}} AND l_i = L_i AND t_i = R_i - r_i <== b_i = 0 <==> L_i < R_i - r_i S_{i+1,C_{i}} = one_state_{S_{i,C_{i}}} AND l_i = L_i - R_i + r_i AND t_i = r_i <== b_i = 1 <==> L_i >= R_i - r_i Figure 9 S_{i+1,k} = S_{i,k} <== C_i != k Figure 10 R_{i+1} = 2^8 * t_{i} AND L_{i+1} = 2^8 * l_{i} + B_{j_{i}} AND j_{i+1} = j_{i} + 1 <== t_{i} < 2^8 R_{i+1} = t_{i} AND L_{i+1} = l_{i} AND j_{i+1} = j_{i} <== t_{i} >= 2^8 Figure 11 R_{0} = 65280 Figure 12 L_{0} = 2^8 * B_{0} + B_{1} Figure 13 j_{0} = 2 Figure 14 3.8.1.1.1. Termination The range coder can be used in 3 modes. Niedermayer, et al. Expires 30 October 2020 [Page 16] Internet-Draft FFV1 April 2020 * 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 1 byte shorter than the open mode. * In "Sentinel mode" the exact length in bytes is not known and thus the range decoder MAY read into the data that follows the range coded bytestream by one byte. In "Sentinel mode", the end of the range coded bytestream is a binary symbol with state 129, which value SHALL be discarded. After reading this symbol, the range decoder will have read one byte beyond the end of the range coded bytestream. This way the byte position of the end can be determined. Bytestreams written in "Sentinel mode" can be read in "Closed mode" if the length can be determined, in this case the last (sentinel) symbol will be read non-corrupted and be of value 0. Above describes the range decoding, encoding is defined as any process which produces a decodable bytestream. There are 3 places where range coder termination is needed in FFV1. First is in the "Configuration Record", in this case the size of the range coded bytestream is known and handled as "Closed mode". Second is the switch from the "Slice Header" which is range coded to Golomb coded slices as "Sentinel mode". Third is the end of range coded Slices which need to terminate before the CRC at their end. This can be handled as "Sentinel mode" or as "Closed mode" if the CRC position has been determined. 3.8.1.2. Range Non Binary Values To encode scalar integers, it would be possible to encode each bit separately and use the past bits as context. However that would mean 255 contexts per 8-bit symbol that is not only a waste of memory but also requires more past data to reach a reasonably good estimate of the probabilities. Alternatively assuming a Laplacian distribution and only dealing with its variance and mean (as in Huffman coding) would also be possible, however, for maximum flexibility and simplicity, the chosen method uses a single symbol to encode if a number is 0, and if not, encodes the number using its exponent, mantissa and sign. The exact contexts used are best described by Figure 15, followed by some comments. Niedermayer, et al. Expires 30 October 2020 [Page 17] Internet-Draft FFV1 April 2020 pseudo-code | type --------------------------------------------------------------|----- void put_symbol(RangeCoder *c, uint8_t *state, int v, int \ | is_signed) { | int i; | put_rac(c, state+0, !v); | if (v) { | int a= abs(v); | int e= log2(a); | | for (i = 0; i < e; i++) { | put_rac(c, state+1+min(i,9), 1); //1..10 | } | | put_rac(c, state+1+min(i,9), 0); | for (i = e-1; i >= 0; i--) { | put_rac(c, state+22+min(i,9), (a>>i)&1); //22..31 | } | | if (is_signed) { | put_rac(c, state+11 + min(e, 10), v < 0); //11..21| } | } | } | Figure 15: A pseudo-code description of the contexts of Range Non Binary Values. 3.8.1.3. Initial Values for the Context Model At keyframes all Range coder state variables are set to their initial state. 3.8.1.4. State Transition Table one_state_{i} = default_state_transition_{i} + state_transition_delta_{i} Figure 16 zero_state_{i} = 256 - one_state_{256-i} Figure 17 3.8.1.5. default_state_transition Niedermayer, et al. Expires 30 October 2020 [Page 18] Internet-Draft FFV1 April 2020 0, 0, 0, 0, 0, 0, 0, 0, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 94, 95, 96, 97, 98, 99,100,101,102,103, 104,105,106,107,108,109,110,111,112,113,114,114,115,116,117,118, 119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,133, 134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149, 150,151,152,152,153,154,155,156,157,158,159,160,161,162,163,164, 165,166,167,168,169,170,171,171,172,173,174,175,176,177,178,179, 180,181,182,183,184,185,186,187,188,189,190,190,191,192,194,194, 195,196,197,198,199,200,201,202,202,204,205,206,207,208,209,209, 210,211,212,213,215,215,216,217,218,219,220,220,222,223,224,225, 226,227,227,229,229,230,231,232,234,234,235,236,237,238,239,240, 241,242,243,244,245,246,247,248,248, 0, 0, 0, 0, 0, 0, 0, 3.8.1.6. Alternative State Transition Table The alternative state transition table has been built using iterative minimization of frame sizes and generally performs better than the default. To use it, the "coder_type" (see Section 4.1.3) MUST be set to 2 and the difference to the default MUST be stored in the "Parameters", see Section 4.1. The reference implementation of FFV1 in FFmpeg uses Figure 18 by default at the time of this writing when Range coding is used. Niedermayer, et al. Expires 30 October 2020 [Page 19] Internet-Draft FFV1 April 2020 0, 10, 10, 10, 10, 16, 16, 16, 28, 16, 16, 29, 42, 49, 20, 49, 59, 25, 26, 26, 27, 31, 33, 33, 33, 34, 34, 37, 67, 38, 39, 39, 40, 40, 41, 79, 43, 44, 45, 45, 48, 48, 64, 50, 51, 52, 88, 52, 53, 74, 55, 57, 58, 58, 74, 60,101, 61, 62, 84, 66, 66, 68, 69, 87, 82, 71, 97, 73, 73, 82, 75,111, 77, 94, 78, 87, 81, 83, 97, 85, 83, 94, 86, 99, 89, 90, 99,111, 92, 93,134, 95, 98,105, 98, 105,110,102,108,102,118,103,106,106,113,109,112,114,112,116,125, 115,116,117,117,126,119,125,121,121,123,145,124,126,131,127,129, 165,130,132,138,133,135,145,136,137,139,146,141,143,142,144,148, 147,155,151,149,151,150,152,157,153,154,156,168,158,162,161,160, 172,163,169,164,166,184,167,170,177,174,171,173,182,176,180,178, 175,189,179,181,186,183,192,185,200,187,191,188,190,197,193,196, 197,194,195,196,198,202,199,201,210,203,207,204,205,206,208,214, 209,211,221,212,213,215,224,216,217,218,219,220,222,228,223,225, 226,224,227,229,240,230,231,232,233,234,235,236,238,239,237,242, 241,243,242,244,245,246,247,248,249,250,251,252,252,253,254,255, Figure 18: Alternative state transition table for Range coding. 3.8.2. Golomb Rice Mode The end of the bitstream of the "Frame" is filled with 0-bits until that the bitstream contains a multiple of 8 bits. 3.8.2.1. Signed Golomb Rice Codes This coding mode uses Golomb Rice codes. The VLC is split into 2 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. Niedermayer, et al. Expires 30 October 2020 [Page 20] Internet-Draft FFV1 April 2020 pseudo-code | type --------------------------------------------------------------|----- int get_ur_golomb(k) { | for (prefix = 0; prefix < 12; prefix++) { | if (get_bits(1)) { | return get_bits(k) + (prefix << k) | } | } | return get_bits(bits) + 11 | } | | int get_sr_golomb(k) { | v = get_ur_golomb(k); | if (v & 1) return - (v >> 1) - 1; | else return (v >> 1); | } 3.8.2.1.1. Prefix +----------------+-------+ | bits | value | +================+=======+ | 1 | 0 | +----------------+-------+ | 01 | 1 | +----------------+-------+ | ... | ... | +----------------+-------+ | 0000 0000 01 | 9 | +----------------+-------+ | 0000 0000 001 | 10 | +----------------+-------+ | 0000 0000 0001 | 11 | +----------------+-------+ | 0000 0000 0000 | ESC | +----------------+-------+ Table 1 3.8.2.1.2. Suffix +---------+--------------------------------------------------+ +=========+==================================================+ | non ESC | the k least significant bits MSB first | +---------+--------------------------------------------------+ | ESC | the value - 11, in MSB first order, ESC may only | | | be used if the value cannot be coded as non ESC | +---------+--------------------------------------------------+ Niedermayer, et al. Expires 30 October 2020 [Page 21] Internet-Draft FFV1 April 2020 Table 2 3.8.2.1.3. Examples +-----+-------------------------+-------+ | k | bits | value | +=====+=========================+=======+ | 0 | "1" | 0 | +-----+-------------------------+-------+ | 0 | "001" | 2 | +-----+-------------------------+-------+ | 2 | "1 00" | 0 | +-----+-------------------------+-------+ | 2 | "1 10" | 2 | +-----+-------------------------+-------+ | 2 | "01 01" | 5 | +-----+-------------------------+-------+ | any | "000000000000 10000000" | 139 | +-----+-------------------------+-------+ Table 3 3.8.2.2. Run Mode Run mode is entered when the context is 0 and left as soon as a non-0 difference is found. The level is identical to the predicted one. The run and the first different level are coded. 3.8.2.2.1. Run Length Coding The run value is encoded in 2 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 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. Niedermayer, et al. Expires 30 October 2020 [Page 22] Internet-Draft FFV1 April 2020 pseudo-code | type --------------------------------------------------------------|----- log2_run[41]={ | 0, 0, 0, 0, 1, 1, 1, 1, | 2, 2, 2, 2, 3, 3, 3, 3, | 4, 4, 5, 5, 6, 6, 7, 7, | 8, 9,10,11,12,13,14,15, | 16,17,18,19,20,21,22,23, | 24, | }; | | if (run_count == 0 && run_mode == 1) { | if (get_bits(1)) { | run_count = 1 << log2_run[run_index]; | if (x + run_count <= w) { | run_index++; | } | } else { | if (log2_run[run_index]) { | run_count = get_bits(log2_run[run_index]); | } else { | run_count = 0; | } | if (run_index) { | run_index--; | } | run_mode = 2; | } | } | The "log2_run" function is also used within [ISO.14495-1.1999]. 3.8.2.2.2. Level Coding Level coding is identical to the normal difference coding with the exception that the 0 value is removed as it cannot occur: diff = get_vlc_symbol(context_state); if (diff >= 0) { diff++; } 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. Niedermayer, et al. Expires 30 October 2020 [Page 23] Internet-Draft FFV1 April 2020 3.8.2.3. 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. Initial Values for the VLC context state At keyframes all coder state variables are set to their initial state. Niedermayer, et al. Expires 30 October 2020 [Page 24] Internet-Draft FFV1 April 2020 drift = 0; error_sum = 4; bias = 0; count = 1; 4. Bitstream An FFV1 bitstream is composed of a series of 1 or more "Frames" and (when required) a "Configuration Record". Within the following sub-sections, pseudo-code is used to explain the structure of each FFV1 bitstream component, as described in Section 2.2.1. Table 4 lists symbols used to annotate that pseudo- code in order to define the storage of the data referenced in that line of pseudo-code. +--------+----------------------------------------------+ | Symbol | Definition | +========+==============================================+ | u(n) | unsigned big endian integer using n bits | +--------+----------------------------------------------+ | sg | Golomb Rice coded signed scalar symbol coded | | | with the method described in Section 3.8.2 | +--------+----------------------------------------------+ | br | Range coded Boolean (1-bit) symbol with the | | | method described in Section 3.8.1.1 | +--------+----------------------------------------------+ | ur | Range coded unsigned scalar symbol coded | | | with the method described in Section 3.8.1.2 | +--------+----------------------------------------------+ | sr | Range coded signed scalar symbol coded with | | | the method described in Section 3.8.1.2 | +--------+----------------------------------------------+ Table 4: Definition of pseudo-code symbols for this document. The same context that is initialized to 128 is used for all fields in the header. The following MUST be provided by external means during initialization of the decoder: "frame_pixel_width" is defined as "Frame" width in "Pixels". "frame_pixel_height" is defined as "Frame" height in "Pixels". Default values at the decoder initialization phase: Niedermayer, et al. Expires 30 October 2020 [Page 25] Internet-Draft FFV1 April 2020 "ConfigurationRecordIsPresent" is set to 0. 4.1. Parameters The "Parameters" section contains significant characteristics about the decoding configuration used for all instances of "Frame" (in FFV1 version 0 and 1) or the whole FFV1 bitstream (other versions), including the stream version, color configuration, and quantization tables. Figure 19 describes the contents of the bitstream. Niedermayer, et al. Expires 30 October 2020 [Page 26] Internet-Draft FFV1 April 2020 pseudo-code | type --------------------------------------------------------------|----- Parameters( ) { | version | ur if (version >= 3) { | micro_version | ur } | coder_type | ur if (coder_type > 1) { | for (i = 1; i < 256; i++) { | state_transition_delta[ i ] | sr } | } | colorspace_type | ur if (version >= 1) { | bits_per_raw_sample | ur } | chroma_planes | br log2_h_chroma_subsample | ur log2_v_chroma_subsample | ur extra_plane | br if (version >= 3) { | num_h_slices - 1 | ur num_v_slices - 1 | ur quant_table_set_count | ur } | for (i = 0; i < quant_table_set_count; i++) { | QuantizationTableSet( i ) | } | if (version >= 3) { | for (i = 0; i < quant_table_set_count; i++) { | states_coded | br if (states_coded) { | for (j = 0; j < context_count[ i ]; j++) { | for (k = 0; k < CONTEXT_SIZE; k++) { | initial_state_delta[ i ][ j ][ k ] | sr } | } | } | } | ec | ur intra | ur } | } | Figure 19: A pseudo-code description of the bitstream contents. CONTEXT_SIZE is 32. Niedermayer, et al. Expires 30 October 2020 [Page 27] Internet-Draft FFV1 April 2020 4.1.1. version "version" specifies the version of the FFV1 bitstream. Each version is incompatible with other versions: decoders SHOULD reject a file due to an unknown version. Decoders SHOULD reject a file with version <= 1 && ConfigurationRecordIsPresent == 1. Decoders SHOULD reject a file with version >= 3 && ConfigurationRecordIsPresent == 0. +-------+-------------------------+ | value | version | +=======+=========================+ | 0 | FFV1 version 0 | +-------+-------------------------+ | 1 | FFV1 version 1 | +-------+-------------------------+ | 2 | reserved* | +-------+-------------------------+ | 3 | FFV1 version 3 | +-------+-------------------------+ | Other | reserved for future use | +-------+-------------------------+ Table 5 * Version 2 was never enabled in the encoder thus version 2 files SHOULD NOT exist, and this document does not describe them to keep the text simpler. 4.1.2. micro_version "micro_version" specifies the micro-version of the FFV1 bitstream. After a version is considered stable (a micro-version value is assigned to be the first stable variant of a specific version), each new micro-version after this first stable variant is compatible with the previous micro-version: decoders SHOULD NOT reject a file 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 30 October 2020 [Page 28] Internet-Draft FFV1 April 2020 +-------+-------------------------+ | value | micro_version | +=======+=========================+ | 0...3 | reserved* | +-------+-------------------------+ | 4 | first stable variant | +-------+-------------------------+ | Other | reserved for future use | +-------+-------------------------+ Table 6: The definitions for "micro_version" values. * development versions may be incompatible with the stable variants. 4.1.3. coder_type "coder_type" specifies the coder used. +-------+-------------------------------------------------+ | value | coder used | +=======+=================================================+ | 0 | Golomb Rice | +-------+-------------------------------------------------+ | 1 | Range Coder with default state transition table | +-------+-------------------------------------------------+ | 2 | Range Coder with custom state transition table | +-------+-------------------------------------------------+ | Other | reserved for future use | +-------+-------------------------------------------------+ Table 7 Restrictions: If "coder_type" is 0, then "bits_per_raw_sample" SHOULD NOT be > 8. Background: At the time of this writing, there is no known implementations of FFV1 bitstream supporting Golomb Rice algorithm with "bits_per_raw_sample" greater than 8, and Range Coder is prefered. 4.1.4. state_transition_delta "state_transition_delta" specifies the Range coder custom state transition table. Niedermayer, et al. Expires 30 October 2020 [Page 29] Internet-Draft FFV1 April 2020 If "state_transition_delta" is not present in the FFV1 bitstream, all Range coder custom state transition table elements are assumed to be 0. 4.1.5. colorspace_type "colorspace_type" specifies the color space encoded, the pixel transformation used by the encoder, the extra plane content, as well as interleave method. +-------+-------------+----------------+--------------+-------------+ | value | color space | pixel | extra plane | interleave | | | encoded | transformation | content | method | +=======+=============+================+==============+=============+ | 0 | YCbCr | None | Transparency | "Plane" | | | | | | then | | | | | | "Line" | +-------+-------------+----------------+--------------+-------------+ | 1 | RGB | JPEG2000-RCT | Transparency | "Line" | | | | | | then | | | | | | "Plane" | +-------+-------------+----------------+--------------+-------------+ | Other | reserved | reserved for | reserved for | reserved | | | for future | future use | future use | for future | | | use | | | use | +-------+-------------+----------------+--------------+-------------+ Table 8 Restrictions: If "colorspace_type" is 1, then "chroma_planes" MUST be 1, "log2_h_chroma_subsample" MUST be 0, and "log2_v_chroma_subsample" MUST be 0. 4.1.6. chroma_planes "chroma_planes" indicates if chroma (color) "Planes" are present. +-------+---------------------------------+ | value | presence | +=======+=================================+ | 0 | chroma "Planes" are not present | +-------+---------------------------------+ | 1 | chroma "Planes" are present | +-------+---------------------------------+ Table 9 Niedermayer, et al. Expires 30 October 2020 [Page 30] Internet-Draft FFV1 April 2020 4.1.7. bits_per_raw_sample "bits_per_raw_sample" indicates the number of bits for each "Sample". Inferred to be 8 if not present. +-------+-----------------------------------+ | value | bits for each sample | +=======+===================================+ | 0 | reserved* | +-------+-----------------------------------+ | Other | the actual bits for each "Sample" | +-------+-----------------------------------+ Table 10 * Encoders MUST NOT store "bits_per_raw_sample" = 0 Decoders SHOULD accept and interpret "bits_per_raw_sample" = 0 as 8. 4.1.8. log2_h_chroma_subsample "log2_h_chroma_subsample" indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma width ("chroma_width = 2^-log2_h_chroma_subsample^ * luma_width"). 4.1.9. log2_v_chroma_subsample "log2_v_chroma_subsample" indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma height ("chroma_height=2^-log2_v_chroma_subsample^ * luma_height"). 4.1.10. "extra\_plane" "extra_plane" indicates if an extra "Plane" is present. +-------+------------------------------+ | value | presence | +=======+==============================+ | 0 | extra "Plane" is not present | +-------+------------------------------+ | 1 | extra "Plane" is present | +-------+------------------------------+ Table 11 4.1.11. num_h_slices "num_h_slices" indicates the number of horizontal elements of the slice raster. Niedermayer, et al. Expires 30 October 2020 [Page 31] Internet-Draft FFV1 April 2020 Inferred to be 1 if not present. 4.1.12. num_v_slices "num_v_slices" indicates the number of vertical elements of the slice raster. Inferred to be 1 if not present. 4.1.13. quant_table_set_count "quant_table_set_count" indicates the number of Quantization Table Sets. "quant_table_set_count" MUST be less than or equal to 8. Inferred to be 1 if not present. MUST NOT be 0. 4.1.14. states_coded "states_coded" indicates if the respective Quantization Table Set has the initial states coded. Inferred to be 0 if not present. +-------+--------------------------------+ | value | initial states | +=======+================================+ | 0 | initial states are not present | | | and are assumed to be all 128 | +-------+--------------------------------+ | 1 | initial states are present | +-------+--------------------------------+ Table 12 4.1.15. initial_state_delta "initial_state_delta[ i ][ j ][ k ]" indicates the initial Range coder state, it is encoded using "k" as context index and pred = j ? initial_states[ i ][j - 1][ k ] Figure 20 initial_state[ i ][ j ][ k ] = ( pred + initial_state_delta[ i ][ j ][ k ] ) & 255 Niedermayer, et al. Expires 30 October 2020 [Page 32] Internet-Draft FFV1 April 2020 Figure 21 4.1.16. ec "ec" indicates the error detection/correction type. +-------+--------------------------------------------+ | value | error detection/correction type | +=======+============================================+ | 0 | 32-bit CRC on the global header | +-------+--------------------------------------------+ | 1 | 32-bit CRC per slice and the global header | +-------+--------------------------------------------+ | Other | reserved for future use | +-------+--------------------------------------------+ Table 13 4.1.17. intra "intra" indicates the constraint on "keyframe" in each instance of "Frame". Inferred to be 0 if not present. +-------+-------------------------------------------------------+ | value | relationship | +=======+=======================================================+ | 0 | "keyframe" can be 0 or 1 (non keyframes or keyframes) | +-------+-------------------------------------------------------+ | 1 | "keyframe" MUST be 1 (keyframes only) | +-------+-------------------------------------------------------+ | Other | reserved for future use | +-------+-------------------------------------------------------+ Table 14 4.2. Configuration Record In the case of a FFV1 bitstream with "version >= 3", a "Configuration Record" is stored in the underlying "Container", at the track header level. It contains the "Parameters" used for all instances of "Frame". The size of the "Configuration Record", "NumBytes", is supplied by the underlying "Container". Niedermayer, et al. Expires 30 October 2020 [Page 33] Internet-Draft FFV1 April 2020 pseudo-code | type -----------------------------------------------------------|----- ConfigurationRecord( NumBytes ) { | ConfigurationRecordIsPresent = 1 | Parameters( ) | while (remaining_symbols_in_syntax(NumBytes - 4)) { | reserved_for_future_use | br/ur/sr } | configuration_record_crc_parity | u(32) } | 4.2.1. reserved_for_future_use "reserved_for_future_use" has semantics that are reserved for future use. Encoders conforming to this version of this specification SHALL NOT write this value. Decoders conforming to this version of this specification SHALL ignore its value. 4.2.2. configuration_record_crc_parity "configuration_record_crc_parity" 32 bits that are chosen so that the "Configuration Record" as a whole has a crc remainder of 0. This is equivalent to storing the crc remainder in the 32-bit parity. The CRC generator polynomial used is the standard IEEE CRC polynomial (0x104C11DB7) with initial value 0. 4.2.3. Mapping FFV1 into Containers This "Configuration Record" can be placed in any file format supporting "Configuration Records", fitting as much as possible with how the file format uses to store "Configuration Records". The "Configuration Record" storage place and "NumBytes" are currently defined and supported by this version of this specification for the following formats: 4.2.3.1. AVI File Format The "Configuration Record" extends the stream format chunk ("AVI ", "hdlr", "strl", "strf") with the ConfigurationRecord bitstream. See [AVI] for more information about chunks. Niedermayer, et al. Expires 30 October 2020 [Page 34] Internet-Draft FFV1 April 2020 "NumBytes" is defined as the size, in bytes, of the strf chunk indicated in the chunk header minus the size of the stream format structure. 4.2.3.2. ISO Base Media File Format The "Configuration Record" extends the sample description box ("moov", "trak", "mdia", "minf", "stbl", "stsd") with a "glbl" box that contains the ConfigurationRecord bitstream. See [ISO.14496-12.2015] for more information about boxes. "NumBytes" is defined as the size, in bytes, of the "glbl" box indicated in the box header minus the size of the box header. 4.2.3.3. NUT File Format The "codec_specific_data" element (in "stream_header" packet) contains the ConfigurationRecord bitstream. See [NUT] for more information about elements. "NumBytes" is defined as the size, in bytes, of the "codec_specific_data" element as indicated in the "length" field of "codec_specific_data". 4.2.3.4. Matroska File Format FFV1 SHOULD use "V_FFV1" as the Matroska "Codec ID". For FFV1 versions 2 or less, the Matroska "CodecPrivate" Element SHOULD NOT be used. For FFV1 versions 3 or greater, the Matroska "CodecPrivate" Element MUST contain the FFV1 "Configuration Record" structure and no other data. See [Matroska] for more information about elements. "NumBytes" is defined as the "Element Data Size" of the "CodecPrivate" Element. 4.3. Frame A "Frame" is an encoded representation of a complete static image. The whole "Frame" is provided by the underlaying container. 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". Niedermayer, et al. Expires 30 October 2020 [Page 35] Internet-Draft FFV1 April 2020 pseudo-code | type --------------------------------------------------------------|----- Frame( NumBytes ) { | keyframe | br if (keyframe && !ConfigurationRecordIsPresent { | Parameters( ) | } | while (remaining_bits_in_bitstream( NumBytes )) { | Slice( ) | } | } | Architecture overview of slices in a "Frame": +-----------------------------------------------------------------+ +=================================================================+ | first slice header | +-----------------------------------------------------------------+ | first slice content | +-----------------------------------------------------------------+ | first slice footer | +-----------------------------------------------------------------+ | --------------------------------------------------------------- | +-----------------------------------------------------------------+ | second slice header | +-----------------------------------------------------------------+ | second slice content | +-----------------------------------------------------------------+ | second slice footer | +-----------------------------------------------------------------+ | --------------------------------------------------------------- | +-----------------------------------------------------------------+ | ... | +-----------------------------------------------------------------+ | --------------------------------------------------------------- | +-----------------------------------------------------------------+ | last slice header | +-----------------------------------------------------------------+ | last slice content | +-----------------------------------------------------------------+ | last slice footer | +-----------------------------------------------------------------+ Table 15 Niedermayer, et al. Expires 30 October 2020 [Page 36] Internet-Draft FFV1 April 2020 4.4. Slice A "Slice" is an independent spatial sub-section of a "Frame" that is encoded separately from an other region of the same "Frame". The use of more than one "Slice" per "Frame" can be useful for taking advantage of the opportunities of multithreaded encoding and decoding. A "Slice" consists of a "Slice Header" (when relevant), a "Slice Content", and a "Slice Footer" (when relevant). The pseudo-code below describes the contents of a "Slice". pseudo-code | type --------------------------------------------------------------|----- Slice( ) { | if (version >= 3) { | SliceHeader( ) | } | SliceContent( ) | if (coder_type == 0) { | while (!byte_aligned()) { | padding | u(1) } | } | if (version <= 1) { | while (remaining_bits_in_bitstream( NumBytes ) != 0) {| reserved | u(1) } | } | if (version >= 3) { | SliceFooter( ) | } | } | "padding" specifies a bit without any significance and used only for byte alignment. MUST be 0. "reserved" specifies a bit without any significance in this revision of the specification and may have a significance in a later revision of this specification. Encoders SHOULD NOT fill these bits. Decoders SHOULD ignore these bits. Note in case these bits are used in a later revision of this specification: any revision of this specification SHOULD care about avoiding to add 40 bits of content after "SliceContent" for "version" Niedermayer, et al. Expires 30 October 2020 [Page 37] Internet-Draft FFV1 April 2020 0 and 1 of the bitstream. Background: Due to some non-conforming encoders, some bitstreams were found with 40 extra bits corresponding to "error_status" and "slice_crc_parity". As a result, a decoder conforming to the revised specification could not distinguish between a revised bitstream and a buggy bitstream. 4.5. Slice Header A "Slice Header" provides information about the decoding configuration of the "Slice", such as its spatial position, size, and aspect ratio. The pseudo-code below describes the contents of the "Slice Header". pseudo-code | type --------------------------------------------------------------|----- SliceHeader( ) { | slice_x | ur slice_y | ur slice_width - 1 | ur slice_height - 1 | ur for (i = 0; i < quant_table_set_index_count; i++) { | quant_table_set_index[ i ] | ur } | picture_structure | ur sar_num | ur sar_den | ur } | 4.5.1. slice_x "slice_x" indicates the x position on the slice raster formed by num_h_slices. Inferred to be 0 if not present. 4.5.2. slice_y "slice_y" indicates the y position on the slice raster formed by num_v_slices. Inferred to be 0 if not present. 4.5.3. slice_width "slice_width" indicates the width on the slice raster formed by num_h_slices. Inferred to be 1 if not present. Niedermayer, et al. Expires 30 October 2020 [Page 38] Internet-Draft FFV1 April 2020 4.5.4. slice_height "slice_height" indicates the height on the slice raster formed by num_v_slices. Inferred to be 1 if not present. 4.5.5. quant_table_set_index_count "quant_table_set_index_count" is defined as "1 + ( ( chroma_planes || version <= 3 ) ? 1 : 0 ) + ("extra_plane"? 1 : 0 )". 4.5.6. quant_table_set_index "quant_table_set_index" indicates the Quantization Table Set index to select the Quantization Table Set and the initial states for the slice. Inferred to be 0 if not present. 4.5.7. picture_structure "picture_structure" specifies the temporal and spatial relationship of each "Line" of the "Frame". Inferred to be 0 if not present. +-------+-------------------------+ | value | picture structure used | +=======+=========================+ | 0 | unknown | +-------+-------------------------+ | 1 | top field first | +-------+-------------------------+ | 2 | bottom field first | +-------+-------------------------+ | 3 | progressive | +-------+-------------------------+ | Other | reserved for future use | +-------+-------------------------+ Table 16 4.5.8. sar_num "sar_num" specifies the "Sample" aspect ratio numerator. Inferred to be 0 if not present. Niedermayer, et al. Expires 30 October 2020 [Page 39] Internet-Draft FFV1 April 2020 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. 4.5.9. sar_den "sar_den" specifies the "Sample" aspect ratio denominator. Inferred to be 0 if not present. A value of 0 means that aspect ratio is unknown. Encoders MUST write 0 if "Sample" aspect ratio is unknown. If "sar_num" is 0, decoders SHOULD ignore the encoded value and consider that "sar_den" is 0. 4.6. Slice Content A "Slice Content" contains all "Line" elements part of the "Slice". Depending on the configuration, "Line" elements are ordered by "Plane" then by row (YCbCr) or by row then by "Plane" (RGB). pseudo-code | type --------------------------------------------------------------|----- SliceContent( ) { | if (colorspace_type == 0) { | for (p = 0; p < primary_color_count; p++) { | for (y = 0; y < plane_pixel_height[ p ]; y++) { | Line( p, y ) | } | } | } else if (colorspace_type == 1) { | for (y = 0; y < slice_pixel_height; y++) { | for (p = 0; p < primary_color_count; p++) { | Line( p, y ) | } | } | } | } | Niedermayer, et al. Expires 30 October 2020 [Page 40] Internet-Draft FFV1 April 2020 4.6.1. primary_color_count "primary_color_count" is defined as "1 + ( chroma_planes ? 2 : 0 ) + ("extra_plane"? 1 : 0 )". 4.6.2. 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 "ceil( slice_pixel_height / (1 << log2_v_chroma_subsample) )". 4.6.3. slice_pixel_height "slice_pixel_height" is the height in pixels of the slice. Its value is "floor( ( slice_y + slice_height ) * slice_pixel_height / num_v_slices ) - slice_pixel_y". 4.6.4. slice_pixel_y "slice_pixel_y" is the slice vertical position in pixels. Its value is "floor( slice_y * frame_pixel_height / num_v_slices )". 4.7. Line A "Line" is a list of the sample differences (relative to the predictor) of primary color components. The pseudo-code below describes the contents of the "Line". Niedermayer, et al. Expires 30 October 2020 [Page 41] Internet-Draft FFV1 April 2020 pseudo-code | type --------------------------------------------------------------|----- Line( p, y ) { | if (colorspace_type == 0) { | for (x = 0; x < plane_pixel_width[ p ]; x++) { | sample_difference[ p ][ y ][ x ] | } | } else if (colorspace_type == 1) { | for (x = 0; x < slice_pixel_width; x++) { | sample_difference[ p ][ y ][ x ] | } | } | } | 4.7.1. 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 "ceil( slice_pixel_width / (1 << log2_h_chroma_subsample) )". 4.7.2. slice_pixel_width "slice_pixel_width" is the width in "Pixels" of the slice. Its value is "floor( ( slice_x + slice_width ) * slice_pixel_width / num_h_slices ) - slice_pixel_x". 4.7.3. slice_pixel_x "slice_pixel_x" is the slice horizontal position in "Pixels". Its value is "floor( slice_x * frame_pixel_width / num_h_slices )". 4.7.4. sample_difference "sample_difference[ p ][ y ][ x ]" is the sample difference for "Sample" at "Plane" "p", y position "y", and x position "x". The "Sample" value is computed based on median predictor and context described in Section 3.2. Niedermayer, et al. Expires 30 October 2020 [Page 42] Internet-Draft FFV1 April 2020 4.8. Slice Footer A "Slice Footer" provides information about slice size and (optionally) parity. The pseudo-code below describes the contents of the "Slice Footer". Note: "Slice Footer" is always byte aligned. pseudo-code | type --------------------------------------------------------------|----- SliceFooter( ) { | slice_size | u(24) if (ec) { | error_status | u(8) slice_crc_parity | u(32) } | } | 4.8.1. slice_size "slice_size" indicates the size of the slice in bytes. Note: this allows finding the start of slices before previous slices have been fully decoded, and allows parallel decoding as well as error resilience. 4.8.2. error_status "error_status" specifies the error status. +-------+--------------------------------------+ | value | error status | +=======+======================================+ | 0 | no error | +-------+--------------------------------------+ | 1 | slice contains a correctable error | +-------+--------------------------------------+ | 2 | slice contains a uncorrectable error | +-------+--------------------------------------+ | Other | reserved for future use | +-------+--------------------------------------+ Table 17 4.8.3. slice_crc_parity "slice_crc_parity" 32 bits that are chosen so that the slice as a whole has a crc remainder of 0. Niedermayer, et al. Expires 30 October 2020 [Page 43] Internet-Draft FFV1 April 2020 This is equivalent to storing the crc remainder in the 32-bit parity. The CRC generator polynomial used is the standard IEEE CRC polynomial (0x104C11DB7), with initial value 0, without pre-inversion and without post-inversion. 4.9. Quantization Table Set The Quantization Table Sets are stored by storing the number of equal entries -1 of the first half of the table (represented as "len - 1" in the pseudo-code below) using the method described in Section 3.8.1.2. The second half doesn't need to be stored as it is identical to the first with flipped sign. "scale" and "len_count[ i ][ j ]" are temporary values used for the computing of "context_count[ i ]" and are not used outside Quantization Table Set pseudo-code. Example: Table: 0 0 1 1 1 1 2 2 -2 -2 -2 -1 -1 -1 -1 0 Stored values: 1, 3, 1 pseudo-code | type --------------------------------------------------------------|----- QuantizationTableSet( i ) { | scale = 1 | for (j = 0; j < MAX_CONTEXT_INPUTS; j++) { | QuantizationTable( i, j, scale ) | scale *= 2 * len_count[ i ][ j ] - 1 | } | context_count[ i ] = ceil( scale / 2 ) | } | MAX_CONTEXT_INPUTS is 5. Niedermayer, et al. Expires 30 October 2020 [Page 44] Internet-Draft FFV1 April 2020 pseudo-code | type --------------------------------------------------------------|----- QuantizationTable(i, j, scale) { | v = 0 | for (k = 0; k < 128;) { | len - 1 | ur for (a = 0; a < len; a++) { | quant_tables[ i ][ j ][ k ] = scale * v | k++ | } | v++ | } | for (k = 1; k < 128; k++) { | quant_tables[ i ][ j ][ 256 - k ] = \ | -quant_tables[ i ][ j ][ k ] | } | quant_tables[ i ][ j ][ 128 ] = \ | -quant_tables[ i ][ j ][ 127 ] | len_count[ i ][ j ] = v | } | 4.9.1. quant_tables "quant_tables[ i ][ j ][ k ]" indicates the quantification table value of the Quantized Sample Difference "k" of the Quantization Table "j" of the Set Quantization Table Set "i". 4.9.2. context_count "context_count[ i ]" indicates the count of contexts for Quantization Table Set "i". "context_count[ i ]" MUST be less than or equal to 32768. 5. Restrictions To ensure that fast multithreaded decoding is possible, starting with "version" 3 and if "frame_pixel_width * frame_pixel_height" is more than 101376, "slice_width * slice_height" MUST be less or equal to "num_h_slices * num_v_slices / 4". Note: 101376 is the frame size in "Pixels" of a 352x288 frame also known as CIF ("Common Intermediate Format") frame size format. For each "Frame", each position in the slice raster MUST be filled by one and only one slice of the "Frame" (no missing slice position, no slice overlapping). Niedermayer, et al. Expires 30 October 2020 [Page 45] Internet-Draft FFV1 April 2020 For each "Frame" with "keyframe" value of 0, each slice MUST have the same value of "slice_x", "slice_y", "slice_width", "slice_height" as a slice in the previous "Frame". 6. Security Considerations Like any other codec, (such as [RFC6716]), FFV1 should not be used with insecure ciphers or cipher-modes that are vulnerable to known plaintext attacks. Some of the header bits as well as the padding are easily predictable. Implementations of the FFV1 codec need to take appropriate security considerations into account, as outlined in [RFC4732]. It is extremely important for the decoder to be robust against malicious payloads. Malicious payloads must not cause the decoder to overrun its allocated memory or to take an excessive amount of resources to decode. The same applies to the encoder, even though problems in encoders are typically rarer. Malicious video streams must not cause the encoder to misbehave because this would allow an attacker to attack transcoding gateways. A frequent security problem in image and video codecs is also to not check for integer overflows in "Pixel" count computations, that is to allocate width * height without considering that the multiplication result may have overflowed the arithmetic types range. The range coder could, if implemented naively, read one byte over the end. The implementation must ensure that no read outside allocated and initialized memory occurs. The reference implementation [REFIMPL] contains no known buffer overflow or cases where a specially crafted packet or video segment could cause a significant increase in CPU load. The reference implementation [REFIMPL] was validated in the following conditions: * 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. Niedermayer, et al. Expires 30 October 2020 [Page 46] Internet-Draft FFV1 April 2020 In all of the conditions above, the decoder and encoder was run inside the [VALGRIND] memory debugger as well as clangs address sanitizer [Address-Sanitizer], which track reads and writes to invalid memory regions as well as the use of uninitialized memory. There were no errors reported on any of the tested conditions. 7. Media Type Definition This section completes the media type registration template defined in [RFC6838] and following [RFC4855]. Type name: video Subtype name: FFV1 Required parameters: None. Optional parameters: This parameter is used to signal the capabilities of a receiver implementation. This parameter MUST NOT be used for any other purpose. "version": The version of the FFV1 encoding as defined by Section 4.1.1. "micro_version": The "micro_version" of the FFV1 encoding as defined by Section 4.1.2. "coder_type": The "coder_type" of the FFV1 encoding as defined by Section 4.1.3. "colorspace_type": The "colorspace_type" of the FFV1 encoding as defined by Section 4.1.5. "bits_per_raw_sample": The "bits_per_raw_sample" of the FFV1 encoding as defined by Section 4.1.7. "max_slices": The value of "max_slices" is an integer indicating the maximum count of slices with a frames of the FFV1 encoding. Encoding considerations: This media type is defined for encapsulation in several audiovisual container formats and contains binary data; see Section 4.2.3. This media type is framed binary data; see Section 4.8 of [RFC6838]. Security considerations: Niedermayer, et al. Expires 30 October 2020 [Page 47] Internet-Draft FFV1 April 2020 See Section 6 of this document. Interoperability considerations: None. Published specification: RFC XXXX. [RFC Editor: Upon publication as an RFC, please replace "XXXX" with the number assigned to this document and remove this note.] Applications which use this media type: Any application that requires the transport of lossless video can use this media type. Some examples are, but not limited to screen recording, scientific imaging, and digital video preservation. Fragment identifier considerations: N/A. Additional information: None. Person & email address to contact for further information: Michael Niedermayer michael@niedermayer.cc (mailto:michael@niedermayer.cc) Intended usage: COMMON Restrictions on usage: None. Author: Dave Rice dave@dericed.com (mailto:dave@dericed.com) Change controller: IETF cellar working group delegated from the IESG. 8. IANA Considerations The IANA is requested to register the following values: * Media type registration as described in Section 7. 9. Appendix A: Multi-theaded decoder implementation suggestions 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). Niedermayer, et al. Expires 30 October 2020 [Page 48] Internet-Draft FFV1 April 2020 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. 10. 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.] 11. Normative References [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, . [ISO.9899.1990] International Organization for Standardization, "Programming languages - C", 1990. [RFC4855] Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, . [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet Denial-of-Service Considerations", RFC 4732, DOI 10.17487/RFC4732, December 2006, . [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", 2018. Niedermayer, et al. Expires 30 October 2020 [Page 49] Internet-Draft FFV1 April 2020 [RFC6716] Valin, JM., Vos, K., and T. Terriberry, "Definition of the Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716, September 2012, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [Matroska] IETF, "Matroska", 2019, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 12. Informative References [AVI] Microsoft, "AVI RIFF File Reference", undated, . [range-coding] Nigel, G. and N. Martin, "Range encoding: an algorithm for removing redundancy from a digitised message.", July 1979. [FFV1_V1] Niedermayer, M., "Commit to release FFV1 version 1", April 2009, . [Address-Sanitizer] The Clang Team, "ASAN AddressSanitizer website", undated, . [YCbCr] Wikipedia, "YCbCr", undated, . [ISO.14496-10.2014] International Organization for Standardization, "Information technology -- Coding of audio-visual objects -- Part 10: Advanced Video Coding", September 2014. [ISO.14496-12.2015] International Organization for Standardization, "Information technology -- Coding of audio-visual objects -- Part 12: ISO base media file format", December 2015. Niedermayer, et al. Expires 30 October 2020 [Page 50] Internet-Draft FFV1 April 2020 [NUT] Niedermayer, M., "NUT Open Container Format", December 2013, . [FFV1_V0] Niedermayer, M., "Commit to mark FFV1 version 0 as non- experimental", April 2006, . [FFV1_V3] Niedermayer, M., "Commit to mark FFV1 version 3 as non- experimental", August 2013, . [REFIMPL] Niedermayer, M., "The reference FFV1 implementation / the FFV1 codec in FFmpeg", undated, . [VALGRIND] Valgrind Developers, "Valgrind website", undated, . [ISO.14495-1.1999] International Organization for Standardization, "Information technology -- Lossless and near-lossless compression of continuous-tone still images: Baseline", December 1999. [HuffYUV] Rudiak-Gould, B., "HuffYUV", December 2003, . Authors' Addresses Michael Niedermayer Email: michael@niedermayer.cc Dave Rice Email: dave@dericed.com Jerome Martinez Email: jerome@mediaarea.net Niedermayer, et al. Expires 30 October 2020 [Page 51]