April 2017

By Mike Walsh

Technology Specialist, Satellite & Media

Ultra High Definition (UHD)

TV Contribution Services

and the use of

High Efficiency

Video Coding (HEVC)

01 UHD & HEVC

1. Introduction

2. Arqiva road map

3. What is UHD ?

4. The ‘scope’ of this paper

5. SDI or IP presentation

6. Video encoding (Compression) of UHD programmes

7. Testing & findings

8. Modulation & coding optionsand satellite bandwidth projections

9. Frame rate conversion

10. Summary of Arqiva’s recent practical assessments

11. Recommendations

Annex – Glossary of Terms

Contents

02 UHD & HEVC

1. Introduction

Following R&D work undertaken by Arqiva in 2015 and 2016, this paper sets out and summarises the findings, proposing a way forward to support the carriage and transportation, primarily by satellite, of UHD content in real-time in a contribution context.

The paper discusses different encoding technologies, quality vs. bitrate, modulation schemes aggressive roll-offs, different manufacturers’ current positions, and also maps compressed bit rate to RF bandwidth, making recommendations for fractional transponder usage.

It presents not only a comprehensive review by Arqiva of current UHD technology developments, but also the outcome and findings of testing in 2016; it is the latter which is expected to be of the greatest value and relevance to the reader.

UHD continues to evolve and, as a result, has the potential to confuse. Different broadcasters and end-users will have different requirements for their UHD services, and so the paper begins by setting out some assumptions in order to establish a ‘common ground’ starting point.

This paper only discusses 4k; at this time, Arqiva is keeping a watching brief on 8k UHD but has not, as yet, conducted any of its own testing.

The paper ends with a summary, followed by Arqiva’s recommendation for a ‘way forward’.

Testing and evaluation is, of course, always ongoing and Arqiva will, during 2017, continue to test other systems and other bit rates with a view to gaining a better understanding of the Quality vs. Bit-Rate vs. Genre (‘QBG’) relationship, and also a more comprehensive assessment of the 60Hz vs. 50Hz comparison.

Additional papers will be published in due course to present relevant findings and output.

2. Arqiva road map – general comment

Arqiva publishes (internally) a Technology Road Map (‘TRM’). This is owned and managed within the Media and Data Networks directorate within Arqiva’s Satellite & Media division.The TRM is aligned closely with the division’s Product and Strategic Road Maps. The TRM is continuously evolving and is republished at least monthly.

There are currently six broad ranging categories from Virtualisation to RF & Spectrum withinthe TRM – all UHD work described herein is within the Encoding category.

Two other related workstreams on the TRM are:

n 4k/UHD for Direct-to-Home (‘DTH’) – In general, being the final component of abroadcast chain, this approach is based on a different (more aggressive) approach toVideo Compression than for contribution, and possibly also based on 8 bits per pixel.

n IP carriage of native, mezzanine and compressed video signals – a significant workstream for Arqiva, intended to eventually replace conventional SDI based transport(and routing/switching) with IP based carriage.

03 UHD & HEVC

3. What is UHD?

For the reader’s benefit, the following paragraph is included and reproduced from an EBU Technical Report, reference TR037:

UHDTV (Ultra-High Definition Television), as a package, was approved by the ITU as thenext generation television standard in October 2015 when ITU-R BT.2020 was published.This standard allows the improvement of virtually all parameters of the current HDTVformats namely

n Spatial Resolution (‘more pixels’)n Temporal Resolution (‘more images a second’)n Colour Gamut (‘more colours’)n Bit-Depth (‘more bits/pixel’)

The ITU (also) propose(d) to add

n Higher Image Dynamic Range (HDR)

4. The ‘scope’ of this paper

This White Paper sets out to offer clarity around UHD in general, presenting background and industry data, but includes findings from Arqiva’s practical testing, assisting the reader in adopting and introducing UHD services.

In the main, this White Paper focuses specifically on a 4k subset of UHD. This is described in Section 4.2.

4.1 The acknowledged benefits of UHD in general

Resolution

UHD/UHDTV, originally known as Super Hi-Vision, incorporates both 8k (7680 pixels x 4320 lines) and 4k (3840 pixels x 2160 lines) versions, with 8k being the ultimate goal and 4k being declared as an ‘interim’ solution. These parameters create an image with greater Spatial Resolution than (1080) HD.

Adoption of a Progressive (‘p’), as opposed to an Interlace (‘i’) format, and migration to the 100/120Hz frame rates creates a format with greater Temporal Resolution.

Other Subjective benefits

Increasing the number of bits/pixel improves grey scale granularity (10-bit delivers 1024 levels, compared with only 256 with 8-bit), resulting in nicer looking pictures, particularly overcoming the ‘contouring’ effect sometimes seen on areas of sky.

Comment: There is an alternative school of thought that 8-bit is sufficient for end-user (DTH) broadcasts, and where current 8-bit HD broadcasts appear to exhibit these artefact, these may in fact be due to low resolution (6 or 7-bit) processing in some consumer TV displays.

04 UHD & HEVC

Therefore, for Contribution services, 10-bit is strongly encouraged for UHD. Additionally, manufacturer’s tests have shown that there is minimal additional bit-rate required in encoding 10-bit over 8-bit.

The adoption of a Wide Colour Gamut (‘WCG’) will offer more vivid colours – ITU recommendation BT.2020 is already agreed and captures this.

The introduction of High Dynamic Range (‘HDR’) will offer improved contrast ratio pictureswith brighter whites, and darker blacks – a number of HDR approaches have been tabled and two front runners have emerged. Compatibility is of concern – Arqiva is keeping a close watching brief.

4.2 Options being adopted by Arqiva its assessment and testing

This report and the work described herein is based on a 4k approach to UHD, as follows:

n ‘4k’ only, i.e. 3840 x 2160 resolution, 10-bitn 50Hz and 60Hz frame rates, Progressive Scann Colour Gamut: Rec BT. 2020n 12 Gbit/s SDI presentation

For the work undertaken so far, specifically, we have not included the following additional options/parameters in our testing

n 8kn 4096 resolution and 24/30/48 frame rates - D-Cinema (not TV) optionsn 100, 120Hz Frame Ratesn HDR

5. SDI or IP presentation

There is currently much discussion around presentation and carriage of UHD 4k signals, whose bitrate based on an uncompressed 50Hz progressive scan configuration is around 12 Gbit/s.

As an interim, the broadcast industry has adopted a four-quadrant approach, where Top Left, Top Right, Bottom Left, and Bottom Right portions are separately presented as four 3 Gbit/s streams. These can be considered as four separate 1080p quadrants, and this format is referred to as QUAD HD.

For our testing so far, we have used pre-recorded content (supplied to us by customers andother third parties), stored in either uncompressed or lightly (‘mezzanine’) compressed format, replayed from servers, and handed off as Quad 1080p UHD, using 4 x 3 Gbit/s HD SDIs, presented in BNC format.

We are aware of a small number of equipment suppliers who are considering using 25 Gbps IP based transport, to carry two 4k 50/60Hz progressive channels. We have not tested this format.

05 UHD & HEVC

6. Video encoding (Compression) of UHD programmes

6.1 MPEG system

By way of an introduction to ‘mainstream’ video encoding formats, MPEG-2 (now over twenty five years old), is globally acknowledged as the baseline format for both contribution and DTH broadcast of SD (576i and 480i) video. By current standards, MPEG-2 is not considered to be a particularly aggressive coding format, but remains heavily used for reasons of compatibility with legacy/first generation decoders.

6.2 MPEG-4

MPEG-4, Part 10, also known as Advanced Video Coding or ‘AVC’, (ITU reference H.264) introduced more recently (1998), has the inherent ability to encode programming at significantly lower bit rates than MPEG-2; its primary application, certainly in the DTH arena, is for HD programming, i.e. 720p, 1080i and 1080p formats.

MPEG-4 is obviously also applicable to a 4k environment, particularly where the 4k signal is considered as a QUAD HD picture (4 x 1080p). Although somewhat ‘cumbersome’, initial implementations (many of which are still in service) operate well, their main limitations being:

n Physical (size) – essentially, this is a ‘four HD systems in parallel’ approachn Synchronisation – care is required to maintain time sync of the four quadrantsn Bit Rates – based on a QUAD HD approach, bit rates, theoretically, need to be four times

those of a 1080p HD system

6.3 HEVC as an alternative to MPEG-4 for 4k/UHD

High Efficiency Video Coding, or ‘HEVC’ (defined by the ITU H.265 spec) is a logical follow-on from MPEG-4 (defined by H.264). It builds on MPEG-4, and offers two significant benefits:

n Firstly, by using improved algorithms, HEVC offersfurther encoding improvements, and for 4k,manufacturers and system integrators claim savings ofup to 30% in respect of required bit rate withoutimpairing picture quality.

n Secondly, an integrated solution overcomes theneed for four systems (as is required using a 4x1080pquadrant MPEG-4 approach), and alleviates anyworries associated with quadrant synchronisation –in all testing carried out by Arqiva, despite using 4x3Gbit/s HD-SDI presentation, we have not experienced

synchronisation problems.

HEVC offers savings of up to 30% in respect of required bit rate without impairing picture quality

6.4 Selecting the most appropriate encoding format

Almost certainly, the preferred encoding format for UHD programming is HEVC, based on equipment compatibility and required bit rate. Early adopters are using QUAD HD MPEG-4 based systems, based purely on equipment availability. There are no other obvious reasons not to use HEVC encoding. For contribution links, the chart below sets out an illustrative comparison.

7. Testing & findings

Between 2015 and 2016, Arqiva has run a number of tests and evaluations, sometimes, with customers. The tests may have varied slightly, but the objectives are, in the main, similar.

7.1 The November 2016 test objectives

This White Paper is largely based around the test set-up of November 2016. The key factors/points for assessment for this testing were:

n Picture Quality vs. Encoded bit rate (both HEVC and MPEG-4) vs. Genren Physical hardware configurationn Variations between manufacturersn Interoperability

These tests were carried out at Arqiva’s Chalfont Grove test laboratory.

7.2 Additional tests

Arqiva is planning further tests in 2017 with a number of equipment manufacturers. These will be at their own premises. Following this testing, this white paper may be re-issued.

40% higher

30% lower

NoNo

since 2015 / 16now (2017)

YESYES

No YES

06 UHD & HEVC

4k UHD

Contribution Bit Rates

MPEG 2reference Mbps MPEG 4

HEVC

1st gen

Reverse (Decoder) compatibility

YES MPEG 2 MPEG 4 HEVC

4k UHD

Current encoder availability

QUAD HD HEVC

Current LatestYESYES

07 UHD & HEVC

8. Modulation and coding options,and satellite bandwidth projections

Optimising the bitrate of the compressed UHD service is an essential starting point. After this,it is also equally important to look at the RF parameters being used for the satellite link in order to maximise the Mbps/MHz throughput efficiency.

Taking the HEVC encoded bit stream as an input to the modulator, it is important to select the most appropriate Modulation (MOD) and Coding (COD) options – the most aggressive MODCOD will deliver the highest Mbps/MHz throughput efficiency, but care needs to be taken not to set the MODCOD to be so aggressive as to compromise the link budget margin.

As a given, the modulation scheme will be at least DVB-S2, and preferably a more advanced scheme, either DVB-S2X (open standard) or NS3, NS4, or CCT (proprietary schemes).

The most significant benefit of the DVB-S2X, NS3, NS4 and CCT schemes is that they offer very tight modulator roll-offs (down to 3%) enabling a higher (by up to 15%) Symbol Rate than would be the case than with DVB-S2. Additionally, the newer modulation schemes offer much improved granularity of MODCOD which enables link margin to be much more effectively utilised:

Note: Use of aggressive roll-off schemes (such as DVB-S2X) are dependent on not only using an appropriate modulator at the uplink – but also deploying matching demodulators at all downlink (takers, affiliates) sites. Whilst migration to DVB-S2X (or other) may therefore require a receive site equipment refresh, the capex cost of this is likely to be a small price to pay given the significant throughput benefit of DVB-S2X (or other) over DVB-S2.

9. Frame rates

9.1 50Hz or 60Hz

We strongly believe that all other things (parameters) being equal, a 60Hz 4k UHD programme will be more demanding than a 50Hz programme based on the same content, due simply to there being 20% more information per second, and therefore 20% more information required to be coded in a 60Hz version of the programme.

This assumption is based on using the same approach to GOP length and GOP structure, which we believe to be reasonable and fair.

Later in 2017, we expect to run side-by-side comparisons of quality vs. bit rate for both 50Hz and 60Hz (progressive scan in both cases) versions of the same content, to assess if the adjustment factor is 20%, or whether it’s slightly less.

DVB-S2X, NS3, NS4 and CCT schemes offer very tight modulatorroll-offs enabling a higher Symbol Rate than would be the case than with DVB-S2

08 UHD & HEVC

9.2 Higher Frame rates – 100Hz and 120Hz

Our work so far has not addressed the higher frame rates of 100Hz and 120Hz – we feel it is currently too early for this to be tested reliably yet.

9.3 Frame Rate Conversion

Almost certainly, most customers will need, at some point in the contribution chain to convert from a 50Hz based format to 60Hz, or vice versa. There are an increasing number of solutions available, from established suppliers.

Note: Exercise care in selecting the most appropriate unit. For example, whilst the S-A-M Alchemist Ph.C is undoubtedly a top end converter, it may not always be necessary toinvest in top-end equipment, for some programming is of lower inherent spatial and/or temporal resolution.

10. Summary of Arqiva’srecent practical assessments

10.1 HEVC Encoding

Based on Sports content with both a relatively high spatial and temporal complexity, Arqiva’s tested a 4:2:2 10 bit contribution 4k UHD 50Hz progressive service using HEVC encoding over the approximate range 40 Mbps to 80 Mbps

Largely subjective assessments, backed-up by objective measurements indicate that the range between 45 and 65 Mbps delivers extremely high quality pictures with little or no artefacts.

Top EndAbove 65 Mbps, some slight improvements may be seen on the most challenging content but these improvements will be imperceptible to all but the most discerning expert viewers. Our own testing suggested that there will certainly be no perceptible benefit in operating at rates as high as 80 Mbps.

Bottom EndWhile it was initially expected that rates below 60 Mbps would exhibit artefacts, there was little evidence of this during the test, and in fact at rates down to 45 Mbps only the expert viewers were able to discern impairments at the those lower rates, and only on the most demanding programme clips. However at rates of 40 Mbps and below, impairments were becoming visible to many viewers.

Note: that when viewing the content at the output of a second concatenated encoder, configured as a 26 Mbps HEVC DTH, the subtle differences at and beyond 60 Mbps which were observed by expert viewers were impossible to discern, probably, as a result of the second (pseudo DTH) encoder. In practice, gradually reducing the bitrate of the contribution link down to 45 Mbps did not result in perceptible impairments at the output of the concatenated decoder.

Between 45 and 65 Mbps delivers extremely high quality pictures with little or no artefacts

09 UHD & HEVC

10.2 Comparison with MPEG-4 based contribution systemsIn November 2016, Arqiva was unable to carry out a side-by-side comparison between MPEG-4 and HEVC encoding. Nevertheless, in our experience and based on other observations in 2015 and earlier in 2016, Arqiva is confident in claiming that HEVC offers significant benefits over MPEG-4 for most programmes, certainly in line with the ‘up to 30%’ claimed by suppliers.

Evidence AArqiva has so far run (or been in involved with running) contribution links for 4k in MPEG-4 at rates between 85 Mbps and 110 Mbps. There is some variation across this range, although not significant, and some equipment manufacturers would not recommend rates below 100 Mbps for MPEG-4.

Based on our findings that HEVC encoding shows no perceptible benefit at rates beyond 65 Mbps, this calculates as at least a 35% saving.

Evidence BComparing performance at the lower end of the scale; our assessment is that the 45 Mbps HEVC service is ‘as good’ (subjectively) as an 85 Mbps MPEG-4 services – this suggests over a 45% saving.

Evidence CDuring Testing in 2015, Arqiva ran side-by-side comparisons, using less demanding content, and concluded that a 40 Mbps HEVC encoded service was extremely similar, subjectively to a 100 Mbps MPEG 4 service, projecting almost 60% savings. Probably this is due to the less demanding (than sport) material.

Note: HEVC is clearly significantly better than MPEG in respect of required bitrates, although the measure of improvement in itself varies depending on picture content/complexity. Also worth noting that as HEVC encoding algorithms continue to improve, required bit rates are expected to fall further. Arqiva will work with individual customers on an ongoing basis so that joint understanding is kept up to date.

10.3 RF bandwidth and transponder occupancyThe Occasional Use business is traditionally based on partial transponder occupancy, typically 9MHz (or multiples of 9 MHz) increments.

Currently, Arqiva is delivering 16 Mbps services in a single 9 MHz slot using DVB-S2. Logically therefore a 4k UHD service at a rate of around 45 Mbps would appear to require 3 times this bandwidth, i.e. a slot of 27 MHz.

Arqiva has done some assessments to evaluate the feasibility of operating into a lower bandwidth, using two key adjustments:

n by adopting a 5% roll-off scheme (such as DVB-S2X or NS3)n because there is sufficient link margin, relaxing the FEC (from 3/4) to 8/9

It therefore becomes feasible to operate a 45 Mbps HEVC in only a double (i.e. 18 MHz) OU transponder slot.

Arqiva is confident in claiming that HEVC offers significant benefits over MPEG-4 for most programmes

10 UHD & HEVC

11. Recommendations

HEVC vs. MPEG-4For the material under test, our initial findings suggest, for backhaul/contribution of 4k UHD programming of a sports genre, that 10bit 4:2:2 HEVC encoding with a variable length GOP based on IBBBP will require between 45 to 60 Mbps to deliver acceptable quality pictures, assuming high quality uncompressed 4k 50Hz input material.

For a given subjective picture quality, we find that HEVC requires significantly lower bit rates than MPEG-4, typically up to 40%, based on the content we used for testing – this may vary with other content based on picture complexity.

Optimum Coding RateIn summary, there seems to be a window, for the material under test, of between 45 Mbps and 60 Mbps – above 60 Mbps, improvements are indiscernible, except to a handful of very expert viewers, and below 45 Mbps, impairments begin to be obvious, and with a very rapid quality vs. bit rate deterioration curve.

Satellite bandwidthFor Occasional Use (OU), satellite capacity is utilised on a ‘part transponder’ basis – ‘slots’ are usually multiples of 6 or 9 MHz; and typically for an HD transmission, a 16 Mbps MPEG-4 channel is configured using DVB-S2 to fit into a 9 MHz slot. Occasionally though for more demanding material, 12 or 18 MHz may be used, to accommodate up to 32 Mbps.

Compared with HD and MPEG-4, both 4k UHD and HEVC are still in their infancies. Many of those operators who are already delivering 4k feeds are using Quad HD MPEG-4 encoding –this requires around 100 – 120 Mbps, and therefore occupies a complete 36 MHz transponder, which is extremely costly.

HEVC’s 40% lower bit rate should therefore reduce the transponder occupancy; based on9 MHz slots, certainly a contribution 4k feed can be accommodated in 3 slots (27MHz), andat the more aggressive end (close to 45 Mbps) of the encoding scale, it will just fit into 2 slots (18 MHz).

Arqiva’s objective therefore is to adopt a coding/modulation configuration which, for most cases, will enable operation using only 18 MHz; to this end, our link budget analysis shows that by relaxing the FEC slightly compared with what we currently use for HD in a single 9 MHz slot operation, 18 MHz is sufficient to carry a 4k UHD signal and still deliver an acceptable link margin.

Note: Link Budgets are fundamentally dictated by Satellite Power (EIRP) and Downlink Receive Dish (‘TVRO’) size/performance, and where FEC is the variable which allows the best compromise between maximising throughput without destroying link margin; The parameters used by Arqiva for HD are well established, but with improving satellite performance (higher EIRPs), there is scope now to relax FEC settings.

Link budgets with clear sky margins can be provided on request.

11 UHD & HEVC

RecommendationArqiva believes that an 18MHz transponder slot, to accommodate a 45 Mbps HEVC encoded transport stream, using DVB-S2X or other advanced scheme with low roll-off with a moderate FEC is an optimum compromise between affordability and picture quality and link margin/availability.

For further information:Telephone: +44 (0)1962 823 434 Email: sales@arqiva.com Web: www.arqiva.com