HEVC Real-time Software
Encoder for 8K Live Video
Applications
Spin Digital​ ​| Whitepaper | December 16, 2020 | Version 1.1.1

Spin Digital Video Technologies GmbH
Helmholtzstraße 2-9. 10587 Berlin, Germany
www.spin-digital.com | info@spin-digital.com

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TABLE OF CONTENTSINTRODUCTION TO 8K: BEYOND RESOLUTION

3

VIDEO CODECS FOR 8K: WHY HEVC

3REQUIREMENTS OF A VIDEO ENCODER FOR LIVE APPLICATIONS

7SPIN ENC LIVE: THE SOLUTION FROM SPIN DIGITAL7USE CASE: 8K LIVE CONTENT DISTRIBUTION

9ENCODER PERFORMANCE

10

EXPERIMENTAL SETUP FOR CODEC COMPARISON10COMPRESSION EFFICIENCY AND ENCODING SPEED FOR 4K

14

COMPRESSION EFFICIENCY AND ENCODING SPEED FOR 8K

15

MAXIMUM BITRATE FOR REAL-TIME OPERATION16MINIMUM END-TO-END LATENCY

17RECOMMENDED BITRATE FOR 8KP60 LIVE

17

CONCLUSIONS

19

REFERENCES

21

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INTRODUCTION TO 8K: BEYOND RESOLUTION

With a total resolution of 7680x4320 pixels, and 4 times more pixels per frame than
4K/UHD-1, the emerging 8K video format (also known as UHD-2) is designed to provide
a stronger sensation of reality and a much more immersive experience in which users
are completely absorbed by the audiovisual content (1). The 8K format puts together
higher pixel counts with High Dynamic Range (HDR), wide color gamut, and potentiallyHigh Frame Rates (HFR) for an overall improved visual experience (2).
Apart from technical improvements of the video quality, recent studies have shown that
8K brings in additional benefits to the subjective perceived quality such as increased
perception of depth and 3-dimensionality, which result, in general, in an increased
sensation of immersion and realness (3), (4), (5).
NHK in Japan has pioneered the development of 8K: it presented the first satellite andbroadband transmissions already in 2008 (6) and currently operates the first and only
8K satellite TV service in the world (7). Beyond broadcasting, 8K is being used in otherapplications such as immersive spaces in museums, public viewing of live events(large-screen visualization), and virtual reality, among others. Trials anddemonstrations of 8K live transmission are being conducted for arts, sports and otherevents (8), (9), (10).

2.

VIDEO CODECS FOR 8K: WHY HEVC

Data storage, transmission, and reproduction of uncompressed 8K video is complex
and expensive. Uncompressed 8K video at the maximum quality (e.g. 8K at 120 fps)
can result in data rates up to 72 Gbps. In order to achieve practical data rates fortransmission with current delivery technologies, advanced compression is needed.
Table 1 shows both the uncompressed and typical compressed data rates for 4K and
8K video formats.

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Table 1.​ Specifications and data rates for 4K and 8K video formats.
4K

4K HFR

8K

8K HFR

3840x2160

3840x2160

7680x4320

7680x4320

Frame rate [Hz]

60

120

60

120

Chroma format

4:2:0

4:2:0

4:2:0

4:2:0

Bit depth

10

10

10

12

HDR: PQ/HLG

HDR: PQ/HLG

HDR: PQ/HLG

HDR PQ/HLG

Color gamut

BT.2020

BT.2020

BT.2020

BT.2020

Uncompressed
bitrate [Mbps]

7,465

14,93029,86071,664Compressed bitrate[Mbps] (typical)

10-40

15-50

40-10060-120Resolution [pixels]

Transfer function

The main challenge of the video encoder is to compress the 8K signal at a relatively
low bitrate​, so that the resulting bitstream can be transmitted over current distribution
networks (Internet, satellite, cable, etc.) in a very ​high quality to ensure the Quality ofExperience (QoE) that the end user expects from an 8K service. In addition, for live
applications, the encoder has to perform the encoding in ​real-time and with
low-latency.
Currently, the video codec landscape is very wide. Different coding standards havebeen issued recently by ISO/IEC MPEG and ITU-T VCEG as well as by the Alliance OpenMedia (AOMedia) in order to meet the requirements of the next generation of media
applications both from the technical and IP licensing perspectives. The rest of thissection presents a summary of the existing video codecs and analyzes theirapplicability for 8K live use cases.
AVC/H.264
H.264/AVC is the most widely used codec for many multimedia applications, including
HDTV broadcasting, VoD, Blu-ray Disc storage, video conferencing, etc (11). The
compression efficiency of H.264, however, is not sufficient for transmitting 8K video
content at high quality and low bitrate.
HEVC/H.265
The HEVC/H.265 video coding standard (12) currently represents the state-of-the-art in
UHD compression for real-time workflows (13). It is capable of reducing the bitrate by
50% for the same quality compared to H.264/AVC. Despite some issues related to IP

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licensing, the HEVC standard has been widely deployed in the media industry, driving
especially the shift to UHD video (14).
8K HEVC real-time encoders are already available, both in hardware (15), (16), (17) andsoftware (18), (19), (20) implementations. It is important to note that the HEVC videocoding standard (as well as with other video coding standards) defines the syntax of
the HEVC streams and the procedure for HEVC decoding, but not the algorithm for
HEVC encoding which is left open for competition among implementations. Therefore,
although the above mentioned HEVC encoders are able to compress 8K videos inreal-time, they may result in very different performance, quality and compression levels
as we will show in the performance evaluation section.
AV1
AV1 has been developed by the AOM with the main objective of being royalty-free forInternet streaming applications. The AV1 codec has been promoted as an alternative to
HEVC with its claimed royalty-free model and potentially higher compression
efficiency.
Different codec comparison studies have shown different results depending on theencoding parameters and selected content. A very recent study has shown that the
AV1 reference encoder can achieve between 18% to 21% average bitrate savings forthe same quality compared to the HEVC reference encoder HM at the cost of 5x higher
encoding complexity (21).
Some optimized AV1 implementations are already available (22), (23), (24) which aretargeted mainly for offline production workflows for OTT platforms or HD low-delay
communications.
MPEG-5 EVC
A new video coding standard called MPEG-5 Part 1 - Essential Video Coding (EVC) was
released in April 2020 by MPEG (25). The EVC standard includes a royalty-free baseline
profile and a royalty-paid main profile. The development of EVC was mainly motivatedby the complex licensing requirements for HEVC which resulted in a more limited than
expected adoption mainly for internet streaming applications. EVC aims to address theuse cases that have not been fully served by HEVC, and is also intended to be analternative (or competitor) to AV1 for its target applications.
VVC/H.266
The new-generation coding standard called Versatile Video Coding (VVC) wascompleted in July 2020 by the Joint Video Experts Team (JVET) of ISO and ITU (26).
The new standard targets a 50% bitrate reduction over HEVC for the same visualquality. In addition to compression efficiency gains, VVC includes tools to support
efficient video coding for HDR video, adaptive streaming, scalable video, screen
content, and immersive applications like 360° video and VR.

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Video Codecs: Complexity vs Coding Efficiency
Table 2 shows comparative results of the reference implementations of VVC (VTM8),
AV1 (AOM), EVC (ETM4.1), and HEVC (HM16.18) with respect to HEVC in terms ofcompression efficiency and encoding complexity (21). Efficiency is computed as theaverage bitrate reduction at the same Peak Signal-to-Noise Ratio (PSNR) of the test
encoder with respect to the HEVC reference encoder (HM16.18). In this study a 4K
broadcast scenario is assumed.

Table 2. ​Comparison of VVC, AV1, EVC, and HEVC with respect to HEVC in terms ofcompression efficiency and encoding complexity
VVC(VTM8)

AV1
(AOM)

EVC
(ETM4.1)

HEVC(HM16.18)

Bitrate reduction

41.9%

18.0%

29.4%

0.0%

Encoding complexity

13.1x

5.0x

6.7x

1.0x

Codec Choice for 8K Live Workflows: HEVCAs shown in Table 2, the VVC reference encoder (VTM8) produces the highest
compression efficiency, with around 42% bitrate reduction compared to HEVC.
However, it introduces the highest computational complexity: 13x times compared to
the HEVC reference encoder. VVC was released very recently and there are not yet
solutions for live encoding for UHD video (4K and 8K). As in previous cases with thelaunch of new coding standards, the first implementations for live encoding will notreach the full potential of the coding standard, and several iterations and optimizations
will be needed.
AV1 is not yet ready for live applications for 4K and 8K video, being mostly used foroffline encoding for VoD scenarios. EVC is very new and there are not yet optimized
implementations for live applications.
As a result, HEVC is the best choice for 8K live workflows. It offers very highcompression efficiency and implementations have achieved very high performanceboth for 8K decoding and encoding for offline and live applications. The licensing
issues affecting HEVC, which have prevented the initial deployment of the codec, havebeen addressed by the licensors and are now well understood, at least in the broadcast
industry.

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REQUIREMENTS OF A VIDEO ENCODER FOR LIVEAPPLICATIONSIn order for a video encoder to operate in a live environment, several requirements interms of performance and features should be fulfilled. These requirements aredescribed below:●

High average encoding speed: The performance of the encoder in frames per
second (fps) should be on average higher than the target video frame rate (e.g.
60 fps), with a sufficient tolerance margin so that the instantaneous speed does
not fall below the target frame rate in case of complex scenes.

●

Stable performance over time: For live applications it is not enough to have aminimum average encoding speed. In addition, it is needed that the encoder
exhibits a stable encoding speed over time in order to prevent frame droppingthat can degrade the temporal continuity of the encoded video.

●

Real-time operation mode: The encoder should process the content at thetarget video resolution and frame rate (e.g. 8K at 60 Hz), but if the underlying
hardware does not have the required computing capacity, the encoder shoulddrop input frames instead of adding encoding delay.

●

HRD compliance: A common method for synchronization of encoders anddecoders in live applications is defined by the so-called Hypothetical Reference
Decoder (HRD) model. The HRD model defines constraints on picture timing,
buffer size and buffer handling. To ensure high-quality and smooth playback,appropriate encoding decisions should be made to prevent buffer overflows
and underflows while providing consistent video quality over time (27).

●4.

I/O modules: The encoder should also be equipped with the I/O modules
required to receive the uncompressed input video and deliver the compressed
output bitstream. A quad link 12G SDI capture module is needed to receive the8K uncompressed signal from the camera or a contribution decoder; and a
streaming server is needed to send out the encoded video using common
protocols such as TS over IP (TSoIP) with RTP for broadcast or HLS/DASH for
Internet distribution.

SPIN ENC LIVE: THE SOLUTION FROM SPIN DIGITAL

Spin Digital has developed a high-quality high-performance HEVC software encoder.
The encoder, called Spin Enc Live, is capable of encoding videos in 4Kp120, 8Kp60, and12Kp30 formats in real-time using recent CPU architectures. It has all the requiredfeatures for demanding broadcasting and live streaming applications.

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The main features of Spin Enc Live are summarized below:●

Flexible software encoder: Spin Enc Live is a software CPU-based encoding
solution that supports different resolutions , frame rates, chroma formats, color
spaces, and bit depths. The software can also be easily updated to new CPUarchitectures to achieve enhanced performance and quality.

●

Broadcast-grade quality: The encoder is based on Spin Digital’s advanced
decision algorithms for fast and high-quality encoding, and relies on a modern
encoder architecture with a very efficient software implementation.

●

Highly optimized: Spin Enc Live has been extensively optimized for highperformance including: SIMD instructions optimization (SSE4.1, AVX2, AVX512,
VNNI), memory optimizations, and a multi-level parallelization that scales tosystems with hundreds of CPU cores.

●

Cost-effective architecture: The solution is based on standard server platforms
that are easy to deploy and scale.

●

Designed for live workflows: The encoder supports key features for live
applications including: real-time operation mode, HRD model compliance,broadcast-level CBR control, constrained VBR control, and modules for input
camera capture (3G- and 12G-SDI) and output streaming (RTP and HLS).

●

Low latency: The encoder is specially optimized to guarantee minimal latencies
in both high-efficiency (long GOP) and low-delay (short GOP) operation modes.

Figure 1 illustrates the block diagram of Spin Enc Live. The encoder captures the 8K
video signal (and corresponding audio) coming from either the production set or acontribution link through a quad link 12G SDI interface. Both audio and video are
encoded in real-time using AAC and HEVC, respectively. Finally, the bitstream istransmitted using a streaming server with support for broadcast (TSoIP - RTP) andInternet (HLS) protocols.

Figure 1. Block diagram of the Spin Digital 8K HEVC real-time software encoder.

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USE CASE: 8K LIVE CONTENT DISTRIBUTION

One of the main use cases of the Spin Digital real-time encoder is the live distributionof 4K and 8K content. Figure 2 shows a simple workflow for live events (13), which
consists of three stages: production, service provider, and receiver. More complex live
workflows with more intermediate stages are also possible in some real-life scenarios.

Figure 2. Example of a live distribution workflow.

The production stage can be either a live venue truck or an on-site production set. In
this stage the contribution signal is created by encoding the video in very high quality
and low delay using, for example, HEVC 4:2:2 10-bit. The contribution signal is delivered
to the service provider (e.g. a broadcasting station) via satellite (typically). Note that insome cases live production such as news or TV programs can also be created in thestation, so no contribution signal may be required.
The service provider stage includes an Integrated Receiver Decoder (IRD) that receives
and decodes the contribution signal, applies local changes such as logo insertion, live
editing, or audio commentary, and sends the resulting video to the distribution encoder.
The encoder compresses the video in HEVC 4:2:0 10-bit using CBR rate control at a
bitrate defined by the operator and transmission channel. The distribution signal canthen be delivered to the final consumer using broadcast transmission (e.g. satellite) or
broadband (e.g. open Internet) networks.
Finally, on the receiving side the distribution signal coming from the service provider isdecoded, rendered and presented on an 8K TV. The 8K decoding can be performed byan integrated decoder in the TV set or by an external hardware or software decoder
connected to the TV.
Table 3 summarizes the technical requirements for 4K/8K live distribution including
formats, typical bitrates, and transport protocols. These requirements are based on
industry recommendations (13) and Spin Digital’s experience in 8K broadcasting andstreaming.

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Table 3. T
​ echnical requirements for 4K/8K live distribution.
4K

8K

4x 3G-SD/1x 12G-SDI, or
IP-based

4x 12G-SDI (2SI), or
IP-based

3840x2160,
50/60 Hz7680x4320,
50/60 Hz

HDR: HLG10 or PQ10

HDR: HLG10 or PQ10

BT.2020

BT.2020HEVC Main 10 (4:2:0)
Level 5.1

HEVC Main 10 (4:2:0)
Level 6.1

10 - 40 Mbps

40 - 100 Mbps

CBR

CBR

Multiplexing (broadcast)

MPEG2-TS

MPEG2-TS / MMT

Multiplexing and packaging(broadband)

MP4/TS
HLS/DASH

MP4/TS
HLS/DASH

Production interface

Resolution and frame rate

Transfer function
Color gamut
Video compression

BitrateRate control

6.

ENCODER PERFORMANCE

The performance of the Spin Digital 8K real-time encoder has been evaluated assuming
the above described live distribution use case. The evaluation includes a comparison ofcompression efficiency and encoding speed with respect to other HEVC encoders, andanalysis of the maximum bit rate and minimum latency in real-time operation mode.
The experimental setup used for the codec comparison is described in detail in thenext section.

6.1.

EXPERIMENTAL SETUP FOR CODEC COMPARISONThe Spin Enc Live encoder has been compared to other three encoders in terms ofcompression efficiency and encoding speed: two open-source HEVC software

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encoders, x265 (v3.4) and SVT-HEVC (v1.5.0); and one HEVC hardware encoder, theNvidia NVENC encoder included in the GeForce RTX 2060 GPU.
Compression efficiency has been computed as the average bitrate increase at thesame objective quality of a test encoder compared to a reference encoder. This metricis also known as the Bjøntegaard Delta (BD)-rate (28). Objective quality has been
computed using a common approach based on the PSNR, but other metrics can beused instead of PSNR such as the Structural SIMilarity (SSIM).
A total of seven 1-minute video sequences in 8Kp60 4:2:0 10-bit format were utilized in
the experiments. The 8K clips were downscaled to generate the 4K versions. The
properties of the input videos are presented in Table 4 and thumbnails in Figure 3.

Table 4. P
​ roperties of the test video sequences.
ProducerType

Spatialcomplexity

Temporalcomplexity

Noise
presence

NHK
Technologies

Timelapse

High

High

None

PSNC

FootageMediumHigh

MediumFuji

NHKTechnologies

Timelapse

Low

Low

None

Haru

NHK
Technologies

FootageMediumLow

Low

Helicopter

NHK
Technologies

FootageHigh

MediumLow

PalmHouse

PSNC

FootageMediumMediumHigh

Superposition

UnigineCGI

MediumMediumNone

BerlinFollowCar

The clips were encoded with the encoders under assessment in a random-accessconfiguration (long GOP) at different bitrates and different presets. Rate control was
configured to be CBR with an HRD buffer of 1000 ms. Two presets were selected for
x265, SVT-HEVC, and NVENC: one representing high-quality encoding and another one
representing high-speed encoding. NVENC was also configured to run at the maximum
possible speed: fast preset and IPPP GOP structure.
The selected encoding parameters for the evaluated codecs are summarized in Table 5.

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BerlinFollowCar

Fuji

Haru

Helicopter

PalmHouse

Superposition
Figure 3. T
​ humbnails of the test video sequences.

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Table 5.​ Encoding parameters used for the BD-rate and performance tests.
x265

SVT-HEVC

NVENC

Spin Enc Live

v3.4

v1.5.0

RTX 2060

v1.0

Presets

medium,ultrafast

3 (high quality),
11 (high speed)

slow,
fast

fast

GOP structure

Dynamic

Hierarchical-8

Rate control

I5BP,

Hierarchical-16

IPPP
CBR

Target bitrates 4K

8 - 48 Mbps

Target bitrates 8K

30 - 120 Mbps

Maximum bitrate

Target bitrate

Intra period

1s

HRD buffer size

1000 ms

The encoders were also evaluated in terms of average encoding speed in fps. For thesetests we selected two high-end computing systems and executed the encoders withthe settings indicated in Table 5 but at a single representative bitrate: ​16 Mbps for 4K
and 4​ 8 Mbps​ for 8K. The specifications of the encoding machines are given in Table 6.

Table 6. E
​ ncoding machines used for the performance tests.
Software encoders

Software encoders

GPU encoder

4K

8K

4K and 8K

2x Intel Xeon Platinum
8260 @ 2.4GHz(2x 24 cores)

4x Intel Xeon Platinum
8280 @ 2.7GHz(4x 28 cores)Intel Xeon Gold 6252
@ 2.10GHz(24 cores)RAM

12x 8GHz @ 2933MHz

24x 16GB @ 2933MHz

6x 16GB @ 2933MHzOS

Ubuntu Server 20.04

CentOS 7.8.2003

Windows 10 - 2004,
OS build 19041.508--

NVIDIA GeForce RTX
2060 - Driver 452.06

CPU

GPU

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COMPRESSION EFFICIENCY AND ENCODING SPEED FOR 4K

Figure 4 shows the obtained BD-rate and encoding speed results for 4K videos on the
48-core workstation. Spin Enc Live is used as the reference for the BR-rate calculation.
As it can be observed, Spin Enc Live - fast is able to achieve very similar compression
efficiency compared to x265 - medium at more than 12 times the encoding speed(182.4 fps vs 15.1 fps). x265, even at its ultrafast preset and at the expense of a rateincrease of 77.5%, cannot reach the target frame rate of 60 fps (achieves only 47.5
fps).

Figure 4​. PSNR BD-rate referred to Spin Enc Live and encoding speed for 4K videos using a
48-core machine.

Spin Enc Live also achieves higher compression efficiency than the other two codecs
with their high-quality presets: SVT-HEVC - 3 (bitrate increase of 52.9%) and NVENC slow (bitrate increase of 27.1%).
Only SVT-HEVC - 11, NVENC (slow and fast), and Spin Enc Live are able to run, on
average, at speeds beyond the target video frame rate of 60 fps. Besides, SVT-HEVC 11, NVENC - fast - IPPP, and Spin Enc Live can run faster than the required frame rate
for 4K HFR (120 fps). In particular, the Spin Enc Live encoder can process 182.4 fps on
the selected 48-core workstation, meaning 3.8 4K frames per second per CPU core.
The fast modes of the software encoders, x265 - ultrafast and SVT-HEVC - 11, produce
noticeably worse compression efficiencies than Spin Enc Live (bitrate increases of
77.5%, and 93.1%, respectively). These encoders result in significant quality losses inorder to increase the encoding speed, which makes them unsuitable forbroadcast-quality video distribution.
The GPU hardware encoder (NVENC) can encode 4K videos in real-time, although it
results in BD-rate losses of up to 33.5% for 60 fps and 57.5% for HFR when comparedto Spin Enc Live.

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COMPRESSION EFFICIENCY AND ENCODING SPEED FOR 8K

The results for 8K videos using the 112-core server are presented Figure 5. Spin Enc
Live is used as the reference for the BD-rate calculation.
As in the 4K case, Spin Enc Live - fast results in a compression efficiency very similar tox265 - medium and it is more than 20 times faster. Even at its ultrafast preset, x265
reaches only 11.2 fps at a bitrate increase of 65.2%, and it is not able to scale and use
effectively the computing resources of the multicore server.

Figure 5​. PSNR BD-rate referred to Spin Enc Live and encoding speed for 8K videos using a
112-core machine.

SVT-HEVC is able to go beyond the performance of x265 - ultrafast and achieves 51.5
fps (not reaching the target 8Kp60), but at the cost of a bitrate increase of 89.6%.
The GPU hardware encoder (NVENC), at least in its current generation, cannot encode
8K at 60 fps with the settings shown in Table 5. In our experiments the maximum
speed in random-access mode is 28 fps with a BD-rate increase of 45.0% and, in its
high-speed configuration (fast preset and IPPP pattern), the encoder reaches 55.9 fps,
but at the expense of 60.2% BD-rate losses.
The results show that only Spin Enc Live is able to run faster than 60 fps. With anaverage encoding speed of 89.8 fps, the encoder can process 0.8 8K frames per
second per CPU core.
Overall, the results show that the Spin Enc Live encoder produces similar quality tooffline encoders (such as x265 - medium) at more than 10 and 20 times the encoding
speed for 4K and 8K videos, respectively, on the selected machines. At the same time,
Spin Enc Live results in similar or higher speeds than other codecs configured in theirfastest presets with a significantly higher compression efficiency.
Compared to hardware encoders integrated on GPUs (e.g. NVENC), Spin Enc Live

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results in higher compression efficiency with a much scalable performance. Spin Enc
Live can process 4K at more than 120 fps in a 48-core workstation, and 8K at morethan 60 fps on a 112 core server at higher quality than all the other codecs that wereanalyzed.

The Spin Digital 8K HEVC real-time encoder produces similar
quality to offline encoders at 20 times the encoding speed, andit results in a noticeable higher quality than real-time hardware
encoders.

6.4.

MAXIMUM BITRATE FOR REAL-TIME OPERATION

An average encoding speed higher than the target frame rate is a necessary but not
sufficient condition to guarantee real-time operation. As mentioned in the requirements
section, the encoder should provide a stable performance over time without dropping
frames when running in real-time operation mode.
We performed an experiment to determine the maximum bitrate that Spin Enc Live canachieve when running in real-time mode for 4K and 8K.
Using the encoding configuration for 4K and 8K live distribution (described in Table 5)
and the two computing systems described in Table 6, we measured the maximum
bitrate that the encoder is able to process in real-time without dropping input frames.
The results are summarized in Table 7.

Table 7. ​Maximum bitrate for real-time operation for 4Kp60, 4Kp120, and 8Kp60​.

No CPU cores
Maximum bitrate

4Kp60

4Kp120

8Kp60

48

48

112

300 Mbps

150 Mbps

120 Mbps

The results show that Spin Enc Live is able to encode 4K and 8K videos at the target
frame rates (4Kp60, 4Kp120, and 8Kp60) with higher maximum bitrates than therecommended ones for high-quality broadcast distribution applications.

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MINIMUM END-TO-END LATENCY

A live video application imposes, in addition, restrictions in terms of end-to-end latency.
This latency (also known as glass-to-glass latency) is defined as the time it takes for avideo frame to travel from the camera to the end-user display.
When taking into account only the encoding and decoding latency but without
considering the effect of other processes in the chain (production, contribution link,delivery, rendering), we can obtain the so-called minimum end-to-end latency. The video
encoder should be configured in such a way that it minimizes its latency for a particularapplication. For the case of 4K/8Kp60 live distribution, the main objective is to deliver
the video signal to the final user at the highest possible quality given a bitrate budget.
In order to achieve the best quality, the encoder can use a long GOP configuration that
results in frame reordering, and therefore higher latency.
We performed an experimental test to measure the minimum end-to-end latency for
Spin Enc Live for 8Kp60 distribution. The encoder was configured in high-efficiency
long-GOP mode with an HRD buffer of 1000 ms (as described in Table 5) and using the
112 core server (described in Table 6).
The end-to-end latency included: 12G-SDI video capture, HEVC encoding, encoder
output buffer, and decoder input buffer and decoder reordering. The results are shownin Table 8.

Table 8. E
​ ncoding and end-to-end latency for 4Kp60 and 8Kp60 distribution.
Configuration

Encoder latency

End-to-end latency

8Kp60 - distribution

1620 ms

2680 ms

The obtained end-to-end latency of around 2.7 s complies with the requirements for
8Kp60 live broadcasting applications. It should be noted that lower end-to-end
latencies can be achieved with Spin Enc Live for other application scenarios. For
example, for contribution use cases a small GOP size and smaller HRD buffer can be
configured resulting in shorter latencies. Addressing these use cases are beyond thescope of this whitepaper.

6.6.

RECOMMENDED BITRATE FOR 8KP60 LIVEThe results presented in previous sections have shown that Spin Enc Live fulfills all therequirements for 8Kp60 live distribution applications including: high compression
efficiency, high performance and encoding speed, real-time operation at the target

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bitrate ranges, and required minimum latency. The main question that remains is whatis the recommended bitrate for 8Kp60 live.
The bitrate should be as low as possible in order to reduce the transmission bandwidth
required to deliver the 8K video and, therefore, reduce cost for service operators. At thesame time, the bitrate should be high enough in order to maintain the QoE expected for
8K.
The HEVC standard specifies a maximum bitrate of 120 Mbps for 8Kp60 (Level 6.1 Main Tier). Experiments conducted by NHK laboratories, using a hardware encoder,concluded that 85 Mbps is the minimum bitrate for broadcast-grade quality (29).
We analyzed the bitrate and quality produced by Spin Enc Live using objective
measurements based on the PSNR and SSIM metrics. Figure 6 shows therate-distortion curves corresponding to the 8K test sequences listed in Table 4 when
encoded in random-access mode with the settings described in Table 5.

Figure 6.​ PSNR vs bitrate (top) and SSIM vs bitrate (bottom) for the 8K test sequences encodedwith Spin Enc Live in random-access mode.

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For most 8K video sequences the encoder produces high quality (PSNR > 38 dB, SSIM >0.93) at 50 Mbps. For the sequences exhibiting high camera noise (e.g. PalmHouse),
the encoder produces medium quality (PSNR 37 dB, SSIM 0.87) at the same 50 Mbps
bitrate.
In addition to the PSNR and SSIM analysis, a complete formal subjective test was
conducted. One of the main conclusions is that Spin Enc Live can produce broadcast-grade quality (MOS > 3.5) between 40 and 60 Mbps (30).
Table 9 summarizes Spin Digital’s recommended configuration for 8K live applications
using Spin Enc Live as a distribution encoder.

Table 9.​ Recommended configuration for 8K live distribution.
Resolution

7680x4320 pixels

Frame rate

Up to 60 fps

Transfer function

HDR: PQ/HLG

Color gamut

BT.2020

Chroma format - bit depth

4:2:0 - 10-bit

HEVC profile-level-tier

HEVC Main 10 - Level 6.1 - Main Tier

HEVC encoder

Spin Enc Live - fast
Intra period: 1s

Encoder configuration

GOP size: 16 frames
HRD: 1000 ms
Rate control: CBR

Recommended system

112 CPU cores: 4x Intel Xeon Platinum 8280

Bitrate40 - 60 Mbps

7.

CONCLUSIONSIn this whitepaper a high-quality high-performance 8K HEVC real-time encoder has
been presented. Spin Enc Live is designed for demanding applications, such as 4K/8K
broadcasting and live streaming, using a software CPU-based solution.
A compression efficiency and performance analysis has shown that Spin Enc Liveproduces quality and compression levels similar to best-in-class offline encoders while,at the same time, providing the necessary performance to process 8K videos inreal-time. The encoder meets the requirements for 8Kp60 broadcast and streaming

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applications: stable real-time operation at up to 120 Mbps, a minimum end-to-end
latency of 2.68 s, and the required I/O modules for complete applications.
The encoder can also be used for other applications than UHD-TV including immersive
live and 360° video. Real-time operation can be achieved for other video formats withan equivalent pixel rate as 8Kp60, for example, 360° video in 12Kp30 format. As morecomputing resources become available with new generations of CPUs higher
resolutions and frame rates will become possible.
Next steps in the development of Spin Enc Live include end-to-end demonstrations of
8K live video with production, encoding, delivery (broadcast and broadband), andplayback on 8K TVs. Additional quality assessments, including formal subjective tests,
are also planned in order to further validate the quality and compression of the encoderand determine the minimum bitrates for different applications.

High-performance Video Codecs

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www.spin-digital.com | info@spin-digital.com

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