The xvc video codec
draft-samuelsson-netvc-xvc-00
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draft-samuelsson-netvc-xvc-00
Network Working Group J. Samuelsson
Internet-Draft P. Hermansson
Intended status: Standards Track Divideon
Expires: September 6, 2018 March 5, 2018
The xvc video codec
draft-samuelsson-netvc-xvc-00
Abstract
This document presents a high-level technical description of the xvc
video codec. The xvc video codec is a novel video codec that was
released in its first version in September 2017. This document
provides some technical information as well as a discussion section
around how the xvc codec meets the objectives of the NETVC Working
Group. The document also includes results comparing a recent
revision of xvc with recent revisions of AV1 and HM for three
different test cases; All-Intra, single pass Random-Access, and
multi-pass Random-Access. The average compression gain (BD-rate for
PSNR-Y) for xvc ranges from 3% to 20% for the different test cases.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Technical overview of the xvc video codec . . . . . . . . . . 3
2.1. Block structure . . . . . . . . . . . . . . . . . . . . . 4
2.2. Intra prediction . . . . . . . . . . . . . . . . . . . . 4
2.3. Inter prediction . . . . . . . . . . . . . . . . . . . . 4
2.4. Transforms . . . . . . . . . . . . . . . . . . . . . . . 5
2.5. Entropy coding . . . . . . . . . . . . . . . . . . . . . 5
2.6. In-loop filtering . . . . . . . . . . . . . . . . . . . . 5
2.7. Restriction flags . . . . . . . . . . . . . . . . . . . . 6
2.8. Version handling . . . . . . . . . . . . . . . . . . . . 6
2.9. Temporal scalability and parallel decoding . . . . . . . 7
3. The xvc reference software . . . . . . . . . . . . . . . . . 8
4. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. All-Intra . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Single pass Random-Access . . . . . . . . . . . . . . . . 10
4.3. Multi-pass Random-Access . . . . . . . . . . . . . . . . 11
4.4. Computational complexity . . . . . . . . . . . . . . . . 11
5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Informative References . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
In September 2017, the new video compression format xvc was released,
with source code publicly available at xvc.io [xvcio]. The xvc codec
is a software-defined video codec with conformance for bitstreams,
decoders, and encoders, defined with reference to the publicly
available reference software. The first version of xvc has been
developed by Divideon but the source code of the reference software
has been made publicly available with a desire to invite to broad
usage and continuous development. The developers of the xvc codec
strongly believe in open, transparent and collaborative processes for
technical development, and the purpose of this contribution is to
provide information about the xvc project and to present xvc as a
candidate for the Internet Video Codec.
The xvc codec was developed with a desire to make efficient
compression methods available to a global market under as open,
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transparent and fair conditions as possible. From the start, the
ambition has been to construct a codec, which is easy to deploy,
taking into account both technical and non-technical considerations.
A deeper analysis of such considerations can be found in the xvc
introduction white paper [xvcWp], which provides additional
background information related to xvc. In summary, it can be said
that one of the most central properties of the xvc codec is that it
is not a frozen codec and there is no desire to make it a frozen
codec. Instead, conformance is defined with respect to the current
official version of the xvc reference software. New versions of the
software may be (and is intended to be) released, with addition and/
or removal of technologies as deemed feasible. This makes it
possible to let the codec evolve over time and ensure that the xvc
codec only make use of functionality that is available for licensing
under the xvc license [xvcLicense].
2. Technical overview of the xvc video codec
The xvc codec has been developed completely from scratch and is built
primarily using technology that has been investigated in MPEG and
VCEG, for example during the HEVC [HEVC] standardization and in
exploratory activities after the finalization of HEVC. One of the
most fundamental technical properties of the xvc codec is that the
different tools (or processing steps) of the codec, have been
isolated within separate conditional clauses, controlled by
information (restriction flags) included in the bitstream. This
makes the xvc codec extremely flexible and it makes it possible to
turn off individual processing steps during run-time, if deemed
necessary. This design principle is inspired by the proposal in
JCTVC-X0034 [Wenger16].
As a summary of the technology in xvc, it can be said that xvc is a
block-based hybrid (inter/intra) codec that operates on raw YUV
pictures and compresses them to a NAL (network abstraction layer)
unit structured bitstream. Each picture in a video sequence is
divided into rectangular blocks of samples, which are predicted from
samples in the same picture (intra prediction) or samples in
previously coded pictures (inter prediction). Residuals are
transformed using non-square transforms and the coded symbols are
compressed using a context-adaptive binary arithmetic coder. Block
boundaries are filtered using a deblocking filter. The xvc codec
supports bit-depths of 8, 10 and 12 bits per sample and chroma
formats 4:2:0, 4:2:2, 4:4:4 and monochrome.
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2.1. Block structure
A picture that is to be encoded with xvc is divided into blocks of
64x64 pixels, called CTUs. A CTU can either be coded in its full
size, or it can be split using a binary split, resulting in two
coding units or a quad-tree split, resulting in four coding units.
These coding units can be further split into smaller blocks of
samples all the way down to coding units of size 4x4 (2x2 for
chroma). The splits of a CTU gives rise to a coding unit tree where
prediction and transform is performed on the leaf of the trees. Two
important differences compared to HEVC can be noted here:
1. In xvc there is no distinction between coding units, prediction
units and transform units.
2. In xvc, transform blocks can be non-square.
In the default configuration of xvc, the intra pictures use one
coding unit tree for luma and a different coding unit tree for
chroma. For inter pictures, a single coding unit tree is used for
all color components.
2.2. Intra prediction
There are 67 intra prediction modes in xvc, representing DC
prediction, planar prediction and 65 different angular directions.
Intra prediction uses previously coded samples to the left and/or
above the current block. Reference samples are filtered before being
used for prediction. For vertical, horizontal and DC prediction
there is also a post filter applied to smooth out the edge to the
neighboring block before applying the transform. There is a scheme
for estimating which modes are most probable to be used for the next
block and through using this scheme the code-words for indicating one
of these "most probable modes" can be made shorter than the code-
words of other modes. Both chroma components of a block are
predicted with the same intra prediction mode, but the chroma
prediction mode does not have to be the same as the luma prediction
mode. There is also a mode in which the chroma samples are predicted
from the luma samples using a linear model.
2.3. Inter prediction
Inter prediction is performed using either uni-prediction (where a
single reference picture is used) or bi-prediction (where two
reference pictures are used). The xvc codec supports translational
motions and affine motions which is applied with different motion
vectors for each 4x4 block of a coding unit. The syntax for
signaling inter prediction contains shortcuts for indicating that a
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candidate motion vector is used (merge mode) with a special case for
when there is no residual (skip mode). Motion interpolation filters
of length up to 8 are used and applied with quarter-pel resolution
for luma. In xvc there is a specific inter prediction mode that
accounts for local changes between neighboring samples in the current
picture and neighboring samples in the reference picture. This mode
gives for example good prediction when the light level of a scene
changes over time.
2.4. Transforms
On the encoder side, residual data can be derived from taking the
original samples of a block and subtract the predicted samples value
of the block. This residual can then be forward transformed to
result in a set of coefficients that are quantized and signaled in
the bitstream. On the decoder side a corresponding (but inverse)
process is applied so that coefficients are inverse-quantized, then
inverse-transformed and then added to the predicted sample values.
In the first version of xvc, a separable DCT-like transform was used
where width and height do not need to be of equal length. The size
of the transform is always the same as the size of the coding unit.
For transforms of size 64, high frequency components are zeroed out.
The latest revision of xvc includes additional transforms that are
evaluated and selected based on Rate-Distortion optimization.
Regardless of the size of the coding unit, transform coefficients are
always coded in subblocks of size 4x4 to enable efficient signaling
of subblocks without coefficients. The xvc codec also uses a scheme
called sign hiding which makes it possible to derive the sign of one
coefficient (instead of signaling it) by rounding the values of the
coefficients of a subblock to match the hiding criteria.
2.5. Entropy coding
A Context Adaptive Binary Arithmetic Coder (CABAC) is used in xvc.
It resembles the entropy coding method in AVC and HEVC. When a
symbol has been coded, the state of the context is updated in order
to adjust the probabilities (i.e. the cost) for signaling the same
symbol when the same conditions occur again in the same picture (i.e.
when the same context is used).
2.6. In-loop filtering
The xvc codec includes a single in-loop filter, which is a deblocking
filter, applied on a 4x4 grid of the picture, but only when certain
conditions are met. For intra pictures, an edge is filtered if and
only if the samples on the different sides of the edge belongs to
different coding units. The filtering operation modifies up to two
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samples on each side of the edge, depending on the local
characteristics of the edge.
2.7. Restriction flags
An xvc bitstream starts with a segment header which provides
information about the properties of the coded video such as width,
height, bitdepth, chroma format etc. The segment header also
contains flags that indicate for each individual tool of the codec
whether the tool is used in this bitstream or not. These flags
correspond to the fundamental design principle in the xvc codec which
is to isolate each individual feature (coding tool) within
conditional clauses. The conditional clauses are evaluated during
run time which means that the decoder is capable of executing both
options of each conditional clause. This makes it easy to evaluate
the impact of a specific tool in terms of compression and in terms of
complexity, without having to compile different versions of the
software for each evaluated combination of tools.
In the xvc software, the restriction flags are used instead of
#define clauses for different tools. This ensures that the whole
codebase is exercised during compilation and makes it easy to verify
that different combinations of tools turned on and off work well
together. The only macro-defined constant in the xvc software is
XVC_HIGH_BITDEPTH, which controls if internal bitdepths above 8 are
supported. The first version of xvc contained 62 restriction flags
that applies to different areas of the codec. The latest revision of
xvc, in the dev branch of the GitHub repository, adds another 14
restriction flags corresponding to new tools that will be part of the
next official version of xvc.
2.8. Version handling
The xvc codec has a simple but powerful scheme for version handling.
All xvc bitstreams include, in the beginning of each segment header,
one syntax element that represents the major version and one syntax
element that represents the minor version.
The major version is increased when non-backwards compatible changes
are introduced, typically when new technology is added to xvc. When
a new major version of xvc is released, all existing decoders need to
be updated in order to support bitstreams of the new major version.
Existing bitstreams do not have to be updated when the major version
of xvc is increased, since new technology is activated only for new
bitstreams that uses the new major version.
The minor version is increased when backwards compatible changes are
introduced. In practice, this occurs when technology is being
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disabled through setting their restriction flag equal to one. When a
new minor version of xvc is released, existing decoders do not need
to be updated immediately, since they already have support for
decoding bitstreams in which the disabled technology is turned off.
However, the xvc license requires that they are updated at some point
so that they do not include support for the technology that is no
longer available in xvc. Existing bitstreams have to be updated when
the minor version of xvc is increased since the new version of the
reference decoder will reject bitstreams with too low minor version
(since they make use of technology that is no longer available in
xvc). In practice, it is expected to be extremely rare that the
minor version has to be increased, but the framework for how to
handle it is in place to ensure that there is always a deployable and
licensable version of xvc available, and that no patent holder (or
"patent troll") would be able to block the codec from being used
altogether.
The separation of major version and minor version makes it possible
to always allow for a transition period when changes are introduced
to the xvc codec. In the case of a major version increase, new
bitstreams will only be created once decoders have been updated to
support the new version. In the case of a minor version increase,
new decoders will not replace old decoders until existing bitstreams
have been updated to use the new minor version. By applying this
scheme, the codec can evolve over time without causing any
interoperability problems.
2.9. Temporal scalability and parallel decoding
The default coding structure of the xvc codec is a static
hierarchical B-picture structure with 15 B-pictures. The length of
the hierarchical structure, called SubGOP, is indicated in the
Segment Header. A SubGOP length of 16 corresponds to 15 B-pictures
in a dyadic hierarchy, forming four temporal layers above temporal
layer zero.
Pictures in temporal layers above 0, only predict from temporal layer
0 or pictures with lower temporal layers within the same SubGOP.
This makes it possible to scale of an arbitrary number of temporal
layers in any SubGOP without affecting decodability of any pictures
outside the same SubGOP. This is a very useful property in a
software decoder since it makes it possible to adjust the decoding
complexity in response to sudden changes in available processing
resources. Instead of freezing the video and build up a delay, the
framerate can momentarily be reduced and full framerate can be
resumed as soon as enough processing resources are available.
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A fixed hierarchical coding structure is also very useful in order to
enable efficient parallel decoding. The xvc reference decoder
includes support for picture level threaded decoding. When decoding
bitstreams with SubGOP length 16 a speed-up factor of between 3x and
4x is typically achieved on a CPU with 4 active physical cores.
Providing support for temporal scalability and picture level parallel
decoding generally comes at a very low cost in terms of compression
performance. However, on very specific sequences there might be a
compression penalty due to the constraint of not predicting from
previously coded pictures in the same or higher temporal layers.
The picture level parallelism that is currently implemented in xvc
can be combined with other tools for parallelism such as tiles,
wavefronts or slices if a higher degree of parallelism is desired,
but support for these tools have not yet been added to xvc.
3. The xvc reference software
The implementation of the xvc reference software has been made from
scratch using C++11. Some of the advantages of C++11 compared to
earlier versions of C++ is improved support for type management,
improved pointer handling, availability of lambda expressions,
threading and useful new keywords such as auto. The xvc
implementation strictly follows the Google C++ Style Guide [cppStyle]
which is a well established formatting recommendation for C++,
intended to provide readability and consistency across various C++
project.
The low-complex design of the decoding process of xvc makes it
possible to run the decoder efficiently on a large variety of
devices. The xvc reference decoder has been demonstrated to run
FullHD decoding in realtime on mobile devices, and a JavaScript xvc
decoder, based on the reference xvc decoder, is able to run xvc
decoding directly in browsers, as shown on the Divideon demo page
[xvcDemo]
The total number of lines of code for the latest revision of the xvc
software is around 24,000. This can be compared to the around
240,000 lines of code in the AV1 software.
4. Results
Experimental results for three different test cases are reported;
All-Intra, single pass Random-Access and multi-pass Random-Access.
The latter two correspond to "High Latency CQP" and "High Latency
Unconstrained" from the Video Codec Testing and Quality Measurement
I-D [Daede17]. The results have been generated using the
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AreWeCompressedYet? framework [AWCY]. The full set of results are
available at https://awcy.divideon.com [DAWCY].
For xvc [xvcSource], the commit
f0b31546a3251aeb43f7928338b12aa349156139, from 2018-02-28 has been
used, with command line parameters: -tune 1 -speed-mode 0 -chroma-qp-
offset-u -1 -chroma-qp-offset-v -1. The chroma qp offset is used to
better match bit distribution between luma and chroma relative to
AV1. The quantizer values that have been used for xvc are: 20, 25,
30, 35, 40.
For AV1 [av1Source], the commit
1a7099443894d07fdf3acbb7e12ed04c2d62b9c5, from 2018-02-02 has been
used, with build settings: -DCONFIG_EXPERIMENTAL=1 and --tune-
content=screen as extra command line argument. The following
quantizer values are used: 20, 32, 43, 55 and 63. For multi-pass
coding the run "debargha-adopted-0104@2018-01-05T00:55:50.198Z" was
copied from AreWeCompressedYet? [AWCY], since that was the most
recent run that was finsihed at the time of this submission. That
run was using commit 5a31bc899b308da9b2cacd339d0b19374a74b906 from
"2018-01-04"
For HM [hmSource], version 16.17 from 2017-10-18 has been used with
the default configuration files provided in the cfg folder of the
source code repository. These configuration files correspond to the
JCT-VC common test conditions described in JCTVC-Z1100 [hmCtc]. The
following quantizer values are used: 20, 25, 30, 35, 40.
For All-Intra, results are presented for the Subset1 test set, and
for the two Random-Access cases results are presented for the
Objective-1-fast test set [Testset].
The tables below show the average percentual rate difference measured
using the Bjontegaard rate difference, also known as BD-
rate [Bjontegaard01]. The BD-rate is measured using the following
objective metrics: PSNR, PSNR-HVS [Egiazarian2006], SSIM [Wang04] and
MSSIM [Wang03].
4.1. All-Intra
In the tables below, results are presented for the Subset1 test set
which consist of 50 different still images.
The following table present results of xvc relative to HM with
numbers indicating the percentual bitrate difference for equivalent
quality (negative numbers means that xvc reduces the bitrate).
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+---------+------+---------+---------+----------+------+---------+
| | PSNR | PSNR Cb | PSNR Cr | PSNR HVS | SSIM | MS SSIM |
+---------+------+---------+---------+----------+------+---------+
| Average | -9.3 | -33.3 | -30.3 | -9.8 | -9.9 | -9.5 |
+---------+------+---------+---------+----------+------+---------+
All-intra xvc relative to HM
The following table present results of xvc relative to AV1 with
numbers indicating the percentual bitrate difference for equivalent
quality (negative numbers means that xvc reduces the bitrate).
+---------+------+---------+---------+----------+------+---------+
| | PSNR | PSNR Cb | PSNR Cr | PSNR HVS | SSIM | MS SSIM |
+---------+------+---------+---------+----------+------+---------+
| Average | -3.1 | -7.4 | -7.9 | -2.1 | -2.8 | -3.0 |
+---------+------+---------+---------+----------+------+---------+
All-intra xvc relative to AV1
4.2. Single pass Random-Access
The following table present results of xvc relative to HM with
numbers indicating the percentual bitrate difference for equivalent
quality (negative numbers means that xvc reduces the bitrate).
+---------+-------+---------+---------+----------+-------+---------+
| | PSNR | PSNR Cb | PSNR Cr | PSNR HVS | SSIM | MS SSIM |
+---------+-------+---------+---------+----------+-------+---------+
| 1080p | -16.8 | -29.9 | -28.9 | -15.0 | -17.9 | -16.8 |
| 1080psc | -13.7 | -44.5 | -40.4 | -15.4 | -16.7 | -17.0 |
| 720p | -20.8 | -30.0 | -32.6 | -20.1 | -23.8 | -22.7 |
| 360p | -26.1 | -24.7 | -28.8 | -26.4 | -30.2 | -29.6 |
| Average | -19.5 | -30.7 | -31.3 | -19.1 | -22.0 | -21.2 |
+---------+-------+---------+---------+----------+-------+---------+
Single pass Random-Access xvc relative to HM
The following table present results of xvc relative to AV1 with
numbers indicating the percentual bitrate difference for equivalent
quality (negative numbers means that xvc reduces the bitrate).
Results are presented for 360p and 720p only, since we were not able
to run encodings for the complete test set for AV1 in time.
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+---------+-------+---------+---------+----------+-------+---------+
| | PSNR | PSNR Cb | PSNR Cr | PSNR HVS | SSIM | MS SSIM |
+---------+-------+---------+---------+----------+-------+---------+
| 720p | -13.3 | -0.8 | -4.4 | -16.4 | -20.2 | -20.5 |
| 360p | -19.7 | -9.6 | -3.4 | -22.5 | -23.0 | -26.1 |
| Average | -16.5 | -5.2 | -3.9 | -19.4 | -21.6 | -23.3 |
+---------+-------+---------+---------+----------+-------+---------+
Single pass Random-Access xvc relative to AV1
4.3. Multi-pass Random-Access
The following table present results of xvc relative to AV1 with
numbers indicating the percentual bitrate difference for equivalent
quality (negative numbers means that xvc reduces the bitrate). The
results for AV1 are imported from AreWeCompressedYet? [AWCY].
+---------+-------+---------+---------+----------+-------+---------+
| | PSNR | PSNR Cb | PSNR Cr | PSNR HVS | SSIM | MS SSIM |
+---------+-------+---------+---------+----------+-------+---------+
| 1080p | -6.0 | -4.5 | -3.2 | -5.6 | -10.9 | -9.7 |
| 1080psc | 8.3 | 18.5 | 15.8 | 5.9 | 6.2 | 3.9 |
| 720p | -0.5 | 0.4 | 4.8 | -1.4 | -6.0 | -5.5 |
| 360p | -15.9 | -6.2 | 11.2 | -19.9 | -19.0 | -21.2 |
| Average | -5.1 | -0.7 | 4.6 | -6.4 | -9.4 | -9.6 |
+---------+-------+---------+---------+----------+-------+---------+
Multi-pass Random-Access xvc relative to AV1
4.4. Computational complexity
The single pass Random-Access configurations have been run on the
same platform (Intel Xeon E5-2660). The encoding times and decoding
times can be used to estimate the computational complexity when
running that particular setting on that particular hardware. On
average the encoding time is around 340% higher for AV1 than for xvc.
The decoding time is around 70% higher for AV1 than for xvc.
5. Discussion
The xvc codec has been developed with the aim of creating the most
efficient video codec that can be made available under a single
reasonable license. Different coding tools have been included based
solely on their technical merits. Technology is replaced or removed
only if the patent holder of that particular technology has requested
for it to be removed, or if the patent holder by other means have
made it clear that they intend to seek royalties for the technology
outside of the xvc licensing program or institute patent litigation
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related to the technology. This approach has made it possible to
make use of the best available technology rather than having to
compromise, exclude and/or design around technology to create a
lesser efficient alternative.
Divideon is in continuous dialog with potential patent holders and
has recently sent out a Call for Patents in xvc [xvcCall], to make
sure that the license actually covers all the necessary technology to
use, implement and distribute conforming xvc implementations. As
with all modern video codecs it is not possible to give a definite
answer to the patent situation, but what is unique with xvc is the
well-defined framework for handling third party patent assertions.
In the Call for Patents in xvc that was sent out by Divideon there
was also a request for feedback regarding the idea of defining a
royalty-free profile of xvc. Hopefully, it will be possible to
create a "safe" and free baseline profile of xvc, simply by requiring
certain restriction flags to be set equal to one in that profile.
The xvc codec is brought to the NETVC Working Group as a candidate
for the Internet Video Codec. The objectives of the Working Group
states that "This WG is chartered to produce a high-quality video
codec that meets the following conditions:
1. Is competitive (in the sense of having comparable or better
performance) with current video codecs in widespread use.
2. Is optimized for use in interactive web applications.
3. Is viewed as having IPR licensing terms that allow it to be
widely implemented and deployed."
The authors of this document believe that xvc is well positioned to
fulfill all of these conditions. A framework with a well-defined
single license and possibly a royalty-free baseline profile ensures
that condition 1 and 3 can both be fulfilled, and the reference
software of xvc constitutes a good example of that the codec (and
especially the decoder) can be run in realtime on common hardware
including mobile devices, and thereby fulfill the second condition.
6. IANA Considerations
This document has no IANA considerations.
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7. Security Considerations
This document has no security considerations.
8. Informative References
[av1Source]
Alliance for Open Media, "The av1 source code", n.d.,
<https://aomedia.googlesource.com/aom/>.
[AWCY] Xiph.Org Foundation, "Are We Compressed Yet?", n.d.,
<https://arewecompressedyet.com>.
[Bjontegaard01]
Bjontegaard, G., "Calculation of average PSNR differences
between RD-curves", 2001, <http://wftp3.itu.int/av-arch/
video-site/0104_Aus/VCEG-M33.doc>.
[cppStyle]
Google, "Google C++ Style Guide", n.d.,
<https://google.github.io/styleguide/cppguide.html>.
[Daede17] Daede, T., Norkin, A., and I. Brailovsky, "Video Codec
Testing and Quality Measurement", IETF NETVC Internet-
Draft draft-ietf-netvc-testing-06, October 2017.
[DAWCY] Xiph.Org Foundation, "Are We Compressed Yet? Divideon
clone", n.d., <https://awcy.divideon.com>.
[Egiazarian2006]
Egiazarian, K., Astola, J., Ponomarenko, N., Lukin, V.,
Battisti, F., and M. Carli, "Two new full-reference
quality metrics based on HVS", Proceedings of the Second
International Workshop on Video Processing and Quality
Metrics for Consumer Electronics VPQM, January 2006.
[HEVC] ISO/IEC/ITU-T, "High efficiency video coding", n.d.,
<https://www.itu.int/rec/T-REC-H.265>.
[hmCtc] Sharman, K. and K. Suehring, "Common test conditions",
2017,
<https://hevc.hhi.fraunhofer.de/svn/svn_HEVCSoftware/>.
[hmSource]
ISO/IEC/ITU-T, "The HM source code", n.d.,
<https://hevc.hhi.fraunhofer.de/svn/svn_HEVCSoftware/>.
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[Testset] Daede, T., "Test Sets", n.d.,
<https://people.xiph.org/~tdaede/sets/>.
[Wang03] Wang, Z., Simoncelli, E., and A. Bovik, "Multiscale
structural similarity for image quality assessment", The
37th Asilomar Conference on Signals, Systems
Computers Volume 2, November 2003.
[Wang04] Wang, Z., Bovik, A., Sheikh, H., and E. Simoncelli, "Image
Quality Assessment: From Error Visibility to Structural
Similarity", issn 1057-7149, IEEE transactions on image
processing Volume 13, number 4, April 2004.
[Wenger16]
Wenger, S., "On profiles and per-feature Flags", 2016,
<http://phenix.int-evry.fr/jct/doc_end_user/
current_document.php?id=10492>.
[xvcCall] Divideon, "Call for Patents in xvc", 2018,
<http://www.releasewire.com/press-releases/
call-for-patents-in-xvc-929388.htm>.
[xvcDemo] Divideon, "Mobile video streaming with xvc", 2018,
<https://www.divideon.com/products-and-services/
mobile-video-streaming-with-xvc/>.
[xvcio] Divideon, "The xvc web page", n.d., <https://xvc.io/>.
[xvcLicense]
Divideon, "The xvc license", n.d.,
<https://xvc.io/license>.
[xvcSource]
Divideon, "The xvc source code", n.d.,
<https://github.com/divideon/xvc/tree/dev>.
[xvcWp] Samuelsson, J. and P. Hermansson, "Introducing xvc - a
Divideon white paper", 2017, <https://www.divideon.com/wp-
content/uploads/2017/09/
Introducing-xvc-a-Divideon-whitepaper-v1.0.pdf>.
Authors' Addresses
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Jonatan Samuelsson
Divideon
Kulstoetarvaegen 14
Stockholm 12240
Sweden
Email: jonatan.samuelsson@divideon.com
Per Hermansson
Divideon
Kulstoetarvaegen 14
Stockholm 12240
Sweden
Email: per.hermansson@divideon.com
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