When covering special events, broadcasters have to mediate between the myriad requirements of news reports, extended clips and full coverage of the event in SD, HD or even 3-D, not to mention the backhaul of extra footage and live interviews.
Major events are a perfect demonstration of the flexibility that today's broadcasters need. While consumers now accept that the once static appliance of the television set has to be upgraded from time to time to receive new services, broadcasters need systems that are future-proof.
That's just what the earliest pioneers of digital broadcasting thought they had when they adopted MPEG-2 compression and first-generation DVB transmission standards. And who can blame them? Twenty years ago, it was state-of-the-art and indeed still gives sterling service on a global scale.
However, over time, it became clear that the signals from this combination were simply too bulky to support next-generation services such as HDTV and 3-D TV. The genesis of a solution came in 1999 with the first publication of an MPEG-4 specification, but it was only in the last few years that a true alternative emerged with the development of MPEG-4 Part 10 (H.264 Advanced Video Coding) compression and new transmission standards such as DVB-T2 and DVB-S2. Together, these developments made serious cuts in last-mile bandwidth requirements, making HDTV and 3-D TV commercially viable.
Many of those blazing the digital broadcasting trail are now augmenting their legacy MPEG-2/DVB networks with the newer technology to support next-generation services, while digital latecomers have the luxury of adopting leaner systems from the outset.
It's not surprising that the standards employed to deliver television to the home get the lion's share of attention both in the specialist press and to a lesser extent the mass media, as it directly affects a large number of people. But what tends to be overlooked is the impact that the contribution or backhaul links can have on bandwidth and quality of viewing experience.
JPEG 2000
Selected for distribution of Digital Cinema in 2005, JPEG 2000 is a picture-by-picture compression scheme now being used in the broadcast space. It features 4:2:2 support and 10-bit resolution (expandable to 12 bits), ultra low latency, lossless and low loss compression, and no quality loss in workflows requiring multigeneration compression. Another advantage over MPEG-2 is that JPEG 2000 does not employ macroblocks. This avoids blocking errors and means that downstream MPEG-4 encoders can optimize the macroblock size independently of earlier compression. Due to JPEG 2000's higher-quality 10-bit pictures, the downstream MPEG-4 encoder is not burdened with encoding errors. These factors combine to give greater compression efficiency, which in turn enables operators to launch additional channels or services. (See Table 1.)
Additionally, after carrying out lab tests comparing JPEG 2000 and MPEG for video distribution over IP, video professionals are increasingly finding that advantages in latency, video quality and performance when handling cascading encodes/decodes make JPEG 2000 solutions far superior to MPEG-based solutions at contribution rates over 30Mb/s. (See Figure 1.)
Stereoscopic 3-D
For 3-D broadcasting, synchronizing the left and right eye images is crucial. It may sound simple; however, in reality, this continues to be a challenge for many video transport systems. The SMPTE Technical Committee 10E is currently developing a standard to define the mapping of the left and right eye signal into a 3Gb/s HD-SDI signal. JPEG 2000-based solutions are ideal for the contribution of full-resolution stereoscopic 3-D, as the wavelet transformation of JPEG 2000 provides the same processing for all pixels, and the frame-by-frame nature of this compression codec provides consistent quality for all images and ensures that errors are not propagated from frame to frame. In order to deliver an excellent viewer experience, home mastering requires left and right eye images in full resolution. High quality needs to be maintained throughout the contribution chain so that editing and production can be performed at the left eye/right eye signals with the maximum resolution and quality. The advantage of this solution is that it provides high video quality through 10-bit dynamic range, full HD resolution for both left and right eye, and low latency.
Flexible encoding
The beauty of JPEG 2000 is that it is extremely flexible. Take, for example, the transport of a full HD feed, which for noncompressed HD-SDI would require a link running at 1.5Gb/s. Visitors to IBC2010 could see mathematically lossless JPEG 2000 encoding, at a typical bit rate of just 600Mb/s. Mathematically lossless compression uses reversible integer wavelet filtering to ensure that the compressed data has all the information of uncompressed SDI video and therefore provides video transport of equal quality, while delivering a bandwidth saving of at least 60 percent.
The advantages of lossless video compression follow naturally from the wavelet nature of JPEG 2000 and are enabled through the following two alternatives:
- Mathematically losslessThis uses reversible integer wavelet filtering to ensure that the compressed data has all the information of uncompressed SDI video and therefore provides video transport of equal quality, but with a typical bandwidth saving of at least 60 percent.
- Visually losslessThis method employs floating point filtering and quantization techniques to provide greater compression with no perceived loss of video quality. Typically, visually lossless JPEG 2000 uses from 120Mb/s-150Mb/s, while the backhaul of uncompressed SDI video needs a 1.5Gb/s pipe.
The arguments in favor of deploying JPEG 2000 lossless video transport as an alternative to uncompressed SDI video in the backhaul chain are now overwhelming. By providing two compression options, visually lossless and mathematically lossless, it is now possible to meet present service and quality requirements for all HD contribution applications. This provides broadcasters and content providers with the opportunity to save bandwidth costs without sacrificing quality.
Quality of service
Using HD-SDI visually lossless JPEG 2000 encoding — which employs floating point filtering and quantization techniques to provide greater compression with no perceived loss of video quality — typically shrinks the bit rate to just 120Mb/s-150Mb/s.
All in all, JPEG 2000 gives broadcasters a great deal of freedom to allocate different bandwidths to various feeds according to the importance of each.
There's little doubt that the broadcast world is moving to IP because of greater efficiencies and the falling costs of fiber. Recent research indicates that presently 60 percent of video contribution network investments are for IP-based solutions, and this move toward IP is accelerating.
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By taking advantage of the inherent flexibility of IP, broadcasters and program producers gain efficient, cost-effective and scalable solutions for professional quality video transport. In addition to IP networks being much more cost-effective than legacy distribution, IP also enables significant setup and running cost savings.
Historically, there have been concerns regarding the inherent quality of service (QoS) of IP networks and the ability to carry time-critical IP packets such as those building up a video stream. These concerns can be addressed by deploying managed networks combined with video gateways supporting forward error correction (FEC), both for the recreation of lost packages and removal of network jitter with advanced buffer management.
It's clear that IP is increasingly moving toward a dominant position for the delivery of video content. By choosing IP-based solutions, the expected lifetime of the infrastructure is extended, because it is relatively easy to introduce new functionality.
Basically, the increased availability of good-quality Ethernet links combined with the high quality enabled by a JPEG 2000 video transport means that broadcasters no longer have to choose between high quality and cost-effectiveness, as the best video gateways now provide both.
Equally important is the distribution network linking the headend to the final distribution point, which — given the high cost of building a network — needs to be both resilient and future-proof.
In the end, success is down to the quality of programming and viewing experience served up by the broadcasters. It's the job of solutions providers to ensure that video networks deliver the best in entertainment so that everyone in the video chain can live happily ever after.
Janne Morstøl is CEO at T-VIPS.
