HD Studio-Quality Video Contribution
Mastering the challenge of “Studio-Quality� video contribution via satellite
MCR
Production@Venue
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HD Studio-Quality Video Contribution
The challenge of studio-quality video contribution
LEVERAGING V-NOVA PERSEUS™ PRO FOR HD “STUDIO-QUALITY” VIDEO CONTRIBUTION VIA SATELLITE
Broadcasters and TV video service providers continuously strive to provide the best possible signal quality to viewers, especially for premium TV content such as live sports where there is zero margin for error.
broadcaster’s MCR where it is processed before being aired. It is critical that the quality of this initial contribution link is not compromised as digital processing carried out at the MCR can amplify any existing impairments, or create new ones.
Delivering the best experience for viewers requires video signal degradation to be kept to a minimum at every single step of the delivery chain.
For this reason, whenever infrastructure and transport costs permit, contribution links should be of the highest possible quality. An HD contribution signal is preferable to an SD signal; 4:2:2 colour 10 bit sampling is better than 4:2:0 8 bit sampling; and a signal with low compression (or not compressed
This is particularly true for the first link of the chain, which brings the video feed from the venue where it is produced to the
at all) is better than one that has been heavily compressed. The requirement for quality must be aligned with cost and feasibility. In general, the higher the signal quality, the greater the bandwidth needed to transport the signal to the MCR. This can be both practically challenging, especially for connections in the field, and costly. The right combination must be found between maximum quality and best cost. This paper will explain how V-Nova’s PERSEUS™ PRO compression technology,
Typical Means of Contributing Video Feeds
MCR Satellite Production@Venue
Edit
Fibre
Mix Storage
3G/4G
Primary Contribution
Potentially degraded HD Feed
HD Studio-Quality Video Contribution
combined with Eutelsat’s end-to-end satellite video transmission and extensive geographic coverage, provides a true alternative or back-up to fibre in terms of quality and bandwidth-efficiency.
TRANSPORTING VIDEO CONTRIBUTIONS Three types of network are most commonly used to carry contribution feeds: Fibre, Satellite and 3G/4G Networks. Fibre Fibre enables the delivery of committed information rates in the range of tens or even hundreds of GBs per second using the IP protocol. Because of its high rate of transport and low cost/Mbit ratio, fibre-based contributions can transport video feeds with relatively low compression rates (i.e. high bitrate signals) to deliver high-quality video feeds. The main disadvantage of fibre is its deployment. Fibre is not available everywhere and connecting a new site to a fibre backbone can take several months. Installing fibre is only economically justifiable if the site being connected has regular traffic. Major events, such as the Olympic Games or Football Championships, also use fibre to enable Host Broadcasters to deliver international TV signals to Rights Holders at the International Broadcast Center. This is generally via a temporary infrastructure. Although the duration of these events is usually only a few days or weeks, the high number of customers and the high qualitative standards expected in these cases call for fibre connectivity.
Satellite Satellite offers the advantage of flexibility and ubiquity, allowing contributions to be carried from any point on the earth’s surface with visibility towards the equatorial orbital arc. Modern Ku-band geostationary satellites interface with portable or nomadic stations (SNG or FlyAway mobile stations with 1.2/1.5m antennas and amplifiers of a few hundred Watts) allowing guaranteed transmission information rates of up to 100 Mbit/s. Satellite also enables very large distances to be covered between the source of the contribution and the MCR, due to the vast footprints of typical geostationary satellites. However, compared to fibre, it has often had a higher cost/Mbit ratio and lower overall throughput. Ka-band Satellites - NewsSpotter With Ka-band technology, and products such as Eutelsat’s «NewsSpotter», satellite is also capable of delivering contributions using native IP protocols via compact, lightweight and easy to transport terminals (typically 70 cm antennas, with transmission power in the range of 2-3 watts). The transmission rates provided by NewsSpotter are in the range of a few Mbit, which is ample for contributing HD Feeds with the quality required for news coverage. LEO Satellites Constellations of low orbit satellites operating in the L-band have also been used for specific news contributions. They normally provide native IP transport at rates of a few hundred kilobits.
Although very practical (the terminals are the size of a small suitcase, with flat antennas), the high cost of connectivity and very low transmission rate limits their use to news contributions from the field in rare isolated contexts, where the maximum of portability is required. 3G/4G Networks 3G/4G networks have gained some market share for news contribution due to their compact form and easy portability: a backpack carrying batteries, an adaptive bitrate encoder and a transmitter using 3G/4G networks. Today’s backpacks can use a combination of multiple 3G or 4G SIMs and allow transport rates up to 10 Mbit, which are enough for HD news contributions. The main drawback is that this solution cannot provide guaranteed bandwidth/ CIR. Overall throughput depends on 3G and 4G network coverage, and on the actual throughput of cells which share capacity with data and voice traffic from other mobile devices in the zone. Also, variable rate video encoders are required due to the “best effort” nature of the connectivity that they provide. Variable rate encoders can generate visible fluctuations in video quality, which is unacceptable for events requiring quality and stability. The 3G/4G backpacks also carry the risk of overloading when multiple backpacks try to access the same 3G/4G cell at the same time, leading to an overload and failure of the contribution link.
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HD Studio-Quality Video Contribution
Video codecs used in contribution feeds
An uncompressed TV signal, whether it is in SD or HD, requires a transmission bandwidth which is too high to be comfortably and cost-effectively transported on a transmission channel. For example, an uncompressed HD 1080i Video Feed, the most widely used format today, requires around 1.5 Gbit/sec throughput. Due to their size, video signals are therefore compressed before transmission. However, compression requirements for contribution in the professional market are not the same as compression requirements for distribution to viewers.
COMPRESSION FOR DISTRIBUTION DIRECT-TO-HOME (DTH) When video is compressed for DTH transmission, the primary purpose of compression is to limit the overall bandwidth and contain distribution costs. To meet this requirement, the ISO/IEC Standardisation Body has developed the well-known MPEG family of codecs (MPEG2, MPEG-4 and HEVC) which allows a single HD video feed to be transported at ~5/6 Mbit/sec, i.e. a compression rate of about 1/300.
COMPRESSION FOR PROFESSIONAL CONTRIBUTION For video feeds exchanged in a professional environment (contribution), the primary goal of the codec is to maintain the quality of the original signal. Video compression is still used to limit transmission costs, but compression is less extreme and higher transport costs can be accepted to avoid compromising the quality of the feed. Compression codecs for the professional video market have been developed by the same ISO/IEC standardisation body. The most popular intra video codec used for
Professional Video exchange is JPEG-2000, which can compress HD video feeds at around 150/200 Mbit/sec, i.e. a compression rate of about 1/10.
“TEMPORAL” AND “INTRA” CODECS Video Codecs can generally be grouped into two families: “Temporal” (or “Long GOP”) compression codecs and “Intra” compression codecs. Temporal or Long GOP compression codecs The popular MPEG-2, MPEG-4 and HEVC are Temporal Compression Codecs. They exploit the temporal correlation between adjacent frames of a video sequence and operate on entire chunks of adjacent frames called “GOP” (Group of Pictures). The concept of the GOP is common to all Temporal Codecs and has evolved with time: MPEG-2 only supported fixed-length GOP (typically 12 frames); dynamic GOP length and longer GOP were introduced in newer Codec releases (MPEG-4 and HEVC). Independent of the GOP length, the compression approach is the same. The first frame is the Reference Frame for the entire GOP and is treated individually, without exploiting any correlation with adjacent frames. The difference between adjacent frames is calculated for the remainder of the GOP. As adjacent frames tend to be very similar, the difference between frames carries much less information and thus compressed more efficiently. The main advantage of Temporal Codecs is their compression efficiency. As the correlation between adjacent frames is generally very high, redundant information is eliminated, resulting in high compression rates. The typical rate of an HD video compressed in MPEG-4 or HEVC ranges from a few to tens of megabits per second.
The main disadvantage is the higher compression delay and sensitivity to transmission errors. A Temporal Codec has to collect a significant portion of frames to form a GOP before starting compression. This means that compression delays can be in the range of a few seconds. Low-latency Temporal Codecs exist, but the latency reduction is often achieved at the expense of lower compression efficiencies, i.e. an overall higher bitrate of the compressed video. As a GOP constitutes a self-contained portion of information, where the content is computed by differences from a reference frame, errors in the transmission chain may be amplified as the GOP progresses or even result in the loss of the entire GOP, causing a longer, visible impairment in the video. Temporal, Long GOP codecs are therefore normally used for applications where higher compression efficiencies are required and a compression delay can be tolerated, in particular DTH transmissions.
Intra compression codecs JPEG-2000 is an Intra Compression Codec. Intra Codecs compress individual video frames one by one as if they were static pictures. There are a number of advantages with this approach which are particularly relevant for High-Quality professional contribution. The compression process of an Intra codec tends to be quite fast, as frames are immediately treated as soon as they are available: the typical delay of an Intra commercial codec is around 1 to 2 frames. As frames are treated individually, any error in the transmission channel will only affect the single frame where the error occurs.
HD Studio-Quality Video Contribution
Another significant characteristic is that processing the frames enables an individual frame-accurate “cut” of transmitted video. This is essential in professional contribution environments where video reaching the MCR is typically used in a live transmission and highlights editing workflow. The main disadvantage of Intra compression codecs is that they often require higher bitrates than Temporal Codecs as they do not use temporal correlation between frames. Intra compression codecs are normally preferred in professional environments and for high-quality contribution. Higher transmission rates are accepted as they have the benefit of lower latency and the possibility for frame-accurate splicing of the video.
VIDEO CODECS AND CONTRIBUTION CHANNELS
shorter GOPs, at the expense of an overall higher bitrate.
Intra compression - and the JPEG-2000 Codec - is preferred whenever the best possible quality of contribution is required. JPEG-2000 is commonly used to perform contributions over fibre and is normally operated at rates in the range of 150/200 Mbps, where it provides a visual quality which is considered equivalent to the uncompressed source. It is not an option for contributions using geostationary satellites, which provide transmission rates up to 80/100 Mbps.
Compressing HD video feeds for professional satellite contribution in MPEG4 AVC normally requires transmission rates up to 40 Mbit which are typically carried in 18 MHz frequency slots.
Generally, MPEG-4 AVC Temporal codecs are used for satellite contribution, and in particular, when better quality is needed, specific profiles of the MPEG-4 standard allow extended colour space (4:2:2) and
The most popular Intra codec used in professional video contribution is JPEG2000. JPEG-2000 requires around 150/200 Mbit to carry compressed HD video feeds at a quality that is almost identical to the original uncompressed signal. It should be stressed that Intra codecs need a guaranteed minimum bandwidth to work correctly at the level of quality required for professional applications. If JPEG-2000 compresses an HD video feed at a lower rate, there is not enough room for the required data rate for proper encoding. This results in the compressed video showing visual degradation, compromising its usability.
In news contribution, reporters often prefer to use easily transportable systems such as 3G/4G backpacks or Ka-band satellite systems like NewsSpotter, which can provide IP connectivity in the range of 10 Mbps. The traditional MPEG-4 «Temporal» Codec is normally used in this context – or ABR (Adaptive Bitrate) modifications - with the same profiles as used for DTH, as the quality is sufficient for news contribution.
Transmission Channels and Codec used for Contribution
JPEG-2000
Channel @ 1/100 Gbit
JPEG-2000
JPEG-2000 @ 150/200 Mbit per HD Channel
MPEG-4 «Pro»
MPEG-4/AVC @ 20/40 Mbit per HD Channel
Channel @ ˜80/100 Mbit
MPEG-4 «Pro»
MPEG-4 Abr Propr Abr
Not guaranteed Up to˜10 Gbit 3G/4G
MPEG-4 Abr propr Abr
MPEG-4 Abr or Proprietary @ 5/6Mbit per HD Channel
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HD Studio-Quality Video Contribution
V-NOVA PERSEUS™ Pro studio-quality Intra coding via satellite
Eutelsat and V-Nova partnered in September 2016 with the aim of leveraging V-Nova technology to strengthen the unique competitive advantage of satellite as the platform which offers the highest image quality at reasonable costs. V-Nova’s PERSEUS™ compression technology is based on an innovative, hierarchical, and parallel approach that achieves higher compression efficiencies than the ISO/IEC MPEG family of Codecs. The PERSEUS™ Pro solution represents an alternative to Codecs such as JPEG-2000 for the professional contribution market. Working with V-Nova, Eutelsat identified the potential in using PERSEUS™ Pro for HD contributions via satellite at the necessary quality required by production studios. Like JPEG-2000, PERSEUS™ Pro is an «Intra Only» codec, however, it is capable of delivering studio quality content at compression rates in the range of 80 Mbps which can easily fit in a satellite transponder. As JPEG-2000 is normally operated at 150/200 Mbit, to compress HD 1080i feeds for professional studio-to-studio contribution environments, this limits its use to applications where fibre connectivity is available. PERSEUS™ Pro enables the delivery of “studio” visual quality feeds at compression rates in the range of 80 Mbit, via satellite. This has the obvious benefit of being able to transmit “Studio” quality content from locations not connected to fibre.
ASSESSING THE QUALITY OF PERSEUS™ PRO FOR STUDIO CONTRIBUTION To prove the advantage of the contribution system, Eutelsat submitted PERSEUS™ Pro to a rigorous quality assessment by expert viewers in May 2017, supported by an independent international research laboratory with extensive experience in the broadcast industry. The tests analysed the robustness of PERSEUS™ Pro vs. JPEG-2000, at compression rates suitable for transport via satellite, when operated by portable transmission facilities such as SNGs or FlyAway antennas.
To ensure the results were comparable with other assessments, the tests were conducted according to recognised metrics in the broadcast industry, using procedures defined by the European Broadcasting Union (EBU) for quality assessments of Contribution Codecs. The EBU’s procedure replicates complex contribution chains, while accounting for possible degradations which might occur along the chain. A typical contribution chain may include several transmission steps, with different digital processes having potential implications on the overall quality of the contribution feed. Several HD test sequences were selected for analysis, to represent a wide range of content. Some sequences were chosen as being particularly “encoder-unfriendly”, while others, such as Football, were chosen to represent content that is commonly broadcast.
The Transmission Facilities used were 1.5 m antennas, operated with 400 Watt amplifiers, which are commonly found on SNGs of Fly E/S in Europe. The G/T and EIRP performances of satellites operated by Eutelsat, when accessed with similar transmission facilities, allow transmission rates in the range of 100 Mbps for professional applications with receive antennas in the range of 2 to 3 meters, which is common among larger professional broadcast studios.
Test sequences were also obtained from down-converted 4k material, to have a rich visual spectrum. All test sequences were 4:2:2 1080i@50 sampled at 10 bit and with YUV10/16 Colour Sampling.
For this reason, tests were carried out at compression rates of 60, 70, 80, 90 and 100 Mbps (video rate).
To test the performance of the Codec, each sequence was compressed three times, with a pixel shift applied between compression steps.
Test Procedure to simulate a complex contribution chain Pixel Shift
Original Uncompressed Test Sequence Source
1. Gen
PS +2V +2H
2. Gen
PS -2V -2H
CODEC Under Test
3rd Generation Test Sequence (evaluated) 3. Gen
HD Studio-Quality Video Contribution
Testing complex contribution chains The three compressions steps were operated at the same rate, e.g. each of the three generations were encoded at 60 Mbps, then 70, 80, etc. The pixel shift forces block-based codecs not to operate on the same blocks, and the different generations simulate the degradations introduced by intermediate MCRs. The two Pixel Shifts had opposite directions (up-right for first and low-left for the second). Border pixels exiting the frame boundaries were discarded, while those entering were replaced by black. The test sequences were compressed in PERSEUS™ Pro version 2.0 and in JPEG2000 (CISCO DCM D9902) and both the 1st generation and 3rd generation sequences were used for testing. Each compressed sequence was initially compared with the reference uncompressed sequence (PERSEUS™ Pro vs. uncompressed and JPEG-2000 vs. uncompressed) to assess the potential degradations of the encoding process. Finally, the PERSEUS™ Pro and JPEG-2000 sequences were compared with each other. A panel of expert viewers analysed the quality on a reference HD Studio Monitor (Dolby PRM-4220) at 3H distance. The sequences were shown in a synchronised presentation of original and encoded versions, through a video mixer with split screen functionality. Each sequence contained all the test clips encoded according to a specific test condition and viewers could freely operate the mixer to change the split point during the presentation. At the end of each play-out, viewers judged the presentation on a score chart. Viewers were not allowed to exchange opinions during the viewing.
TEST RESULTS CONFIRM PERFORMANCE A detailed Test Report has been produced as a separate document by the research laboratory. The following text is extracted from the Executive Summary of the Report:
… for 1080i/25 sequences, V-Nova generally shows lower noise and blockiness compared to Jpeg2000 […] For higher bit rates, resolution is quite the same but for lower bit rates there is a loss of resolution for Jpeg2000. Noise level and blockiness are higher for Jpeg2000 and are clearly visible for lower bit rates … The tests performed by Eutelsat compared the performance of PERSEUS™ Pro and JPEG-2000 at equivalent rates. They demonstrated that at transmission rates which can be achieved via satellite, JPEG-2000 cannot deliver the minimal quality required by HD “Studio Quality” contributions, whereas PERSEUS™ Pro becomes an «enabler» for such applications. The results obtained by Eutelsat complement those from tests previously carried out by V-Nova with independent parties. Their aim was to identify the compression rates at which JPEG-2000 and PERSEUS™ Pro deliver an equivalent visual quality. These tests concluded that PERSEUS™ Pro is on average 30% more efficient than JPEG-2000.
CONCLUSION In this paper we have shown how primary contribution feeds must adhere to strict quality requirements in order to maintain the best possible visual quality throughout the video delivery chain. Through Eutelsat and V-Nova’s partnership, satellite can now transport Intra-only “Studio-Quality” contribution feeds with the required characteristics for premium content such as live sports. For the first time, broadcasters and video service providers have a true alternative or back-up to fibre in terms of quality and bandwidth-efficiency. Combining PERSEUS™ Pro with Eutelsat’s end-to-end satellite video transmission, the unique competitive advantage of satellite is further strengthened as the platform which offers the highest image quality at reasonable costs.
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