Cable operators are facing a significant bandwidth crunch as they transition their networks to all-digital while simultaneously expanding their video offerings in the face of mounting competition. For those in the midst of deploying digital simulcast and switched digital video (SDV) architectures, bandwidth optimization is priority No. 1. However, steps taken now to maximize utilization efficiencies of current bandwidth and per-channel throughput can ease the rollout of personalized video services down the line.

Because of the high stream density requirements, personalized video services place a much greater demand on hardware resources and strain the business model built on legacy equipment and costs. Through intelligent and cost-effective video processing, operators can effectively reduce the stress on their networks while adding new revenue drivers to ease the migration to all-digital. Chief among these drivers is the promise of highly targeted advertising to the subscriber level. Switched digital video Migration of current cable networks to partial or fully switched delivery architectures is a significant trend in the cable industry that can help operators to alleviate bandwidth constraints and build a large number of tiered video services and channel lineups. In an SDV environment, operators take a narrowcast approach and send channels selectively only to those homes that actually tune in to them, thus saving precious network bandwidth by not broadcasting signals to all customers all the time.

With the additional bandwidth freed by SDV, operators can build and deliver many tiers of targeted programming without significant bandwidth allocation, allowing them to truly customize and personalize their services to individual subscriber needs. However, deploying services over an SDV architecture is not without its own challenges, leaving room for further enhancements to the delivery architecture.

SDV deployments can realize significant cost benefits from bandwidth sharing and optimization through the use of high density video processing solutions, allowing each node or region to operate with the level of programming complexity once reserved for the main distribution center. SDV moves the complex processing of the channel lineup far closer to the subscriber, placing heavy demands on edge video processing equipment. Improving SDV and VOD Though operators may not want to hear this, current first-generation re-multiplexers weren’t designed for SDV and video on demand (VOD) environments.

Both SDV and VOD architectures must currently receive constant bit rate (CBR) streams to operate seamlessly and provide a simplified means of filling each available quadrature amplitude modulation (QAM) signal with as much content as possible. In the United States, standard definition (SD) VOD streams are compressed to 3.75 Mbps. With this bit rate, 10 VOD streams fit nicely into the transport of 38.8 Mbps being delivered through a 256-QAM modulator. In an SDV environment, the session resource manager (SRM), the "traffic cop" of the SDV system, keeps track of and calculates the available per-channel capacity when each stream’s bit rate is predictable. Many operators tend to set different constant bit rates to different streams based on the video complexity of those streams. In this case, the SRM need only keep track of how many streams are provisioned, how much total throughput is used, and to which modulator the transport is to be delivered.

But operators pay a price for the simplicity of using CBR video streams throughout the network. While variable bit rate (VBR) compression, used in cable and satellite video broadcasting today, allows for dynamic quantization of video packetized elementary streams (PESs), and therefore provides bit rates that vary according to the complexity of the content, CBR video encoding restricts the total throughput of the video to a maximum bit rate, which is usually set lower than that required for optimal video quality.

When a stream is converted from VBR back to CBR, as is required in today’s SDV architectures, the rate clamper or "transrating" device must look at each frame and make re-quantization decisions that always result in an output capped at a certain bit rate. Streams that were originally allowed to occasionally peak beyond 7-9 Mbps when needed become substantially degraded when they must fit into a 3.75 Mbps envelope. Consequently, the best way to deliver the highest video quality is to preserve the original VBR stream rates. Even with the use of multiple, pre-set capped or CBR rates, the streams seldom are allowed to peak to the maximum bit rate at which they were originally encoded in the true VBR form for delivery as part of a statistical multiplex.

This situation presents a difficult question: How can operators deliver the highest quality and widest variety of programming with the limitations of the current architectures and within the available capacity? The answer is to deliver VBR streams as statistically multiplexed transports to the QAM interfaces. Inherent in the stat-muxing of the streams is the high throughput efficiency and high video quality desired. The same 38.8 Mbps can support more streams without any noticeable degradation in video quality. An operator facing throughput limitations can therefore stat-mux 14 programs within a single QAM stream for a 40 percent increase in throughput efficiency. (See Figure 1.)This solution offers the operator the flexibility to add more services gives subscribers more choice and higher video quality. Status quo stat muxing Why couldn’t early statistical multiplexers provide the same functionality? For closed-loop systems, such an approach would be prohibitively costly to carry out on a large scale. These systems connected the multiplexer directly to the encoders and controlled the individual encoding bit rates through a management feedback loop from the multiplexer to the bank of encoders.

Today, content is delivered to the operator already compressed, and open-loop statistical re-multiplexers have for years taken on the responsibility of re-grooming transports for delivery to the QAM modulator. A key obstacle to deploying these devices in a VOD environment, however, is the recompression process utilizing a high degree of buffering to deliver the promised performance. Latencies of 2 to 4 seconds are not uncommon for these units. Of course, in a typical broadcast environment with a linear delay throughout the network, the subscriber wouldn’t notice the delay. However, this type of delay would add unacceptable delay to the round trip time for subscribers’ "trick play" commands with VOD or to the channel change time in an SDV environment.

Another issue with the existing open-loop re-multiplexers is their low density. Since the current statistical re-multiplexers were designed to handle a broadcast environment, they do not offer the high stream densities required to serve the needs of personalized architectures such as VOD and SDV. The lower density of the current devices also leads to their high per-stream processing costs, making them unsuitable for these environments. Low latency, high density When it comes throughput and video-quality optimization in SDV and VOD environments, first-generation re-multiplexers are simply challenged. Evolving distribution architectures designed for the delivery of enhanced services call for advanced capabilities, such as low-latency response time and high-density video processing.

Without low-latency response times for viewer activity, high-end video services simply don’t have the appeal required to draw in a greater number of active users; and without the cost-efficiency delivered by high-density multiplexers, operators cannot afford to deploy the solutions in the first place.

This approach also allows the operators to share the available QAM signal’s data capacity among multiple services, such as VOD and SDV, and utilize the same resource management application for all services. (See Figure 2.) Targeted ads As more content becomes selectable through subscriber on-demand services for movies, TV programs and other services, more opportunities arise for ads that can be targeted or personalized to the viewer. For example, when VOD content selections are made, operators know the specific subscriber (or least the household) that made the request, naturally aligning VOD services and targeted advertising. And of course making commercials more pertinent to the viewer makes them more valued by the advertiser, allowing operators to charge more and to incrementally see greater revenues.

Zoned and targeted ads present new avenues for revenue growth in local cable advertising and will help offset similar offerings by competitors, including highly targeted Internet advertising. Through the use of advanced video processing technology, ads can be zoned by cities, neighborhoods and even specific demographics, as well as eventually being personalized to individuals based on their prior viewing habits and activities. Ad customization can be based on existing local ad insertion splice point availability from national broadcast feeds or the use of dynamic graphics and text insertion to overlay and supplement the national ad.

Such narrowly targeted and personalized ads, enabled by the emergence of new standards and advanced technologies, are expected to broadly motivate advertisers to increase their overall budgets, as well as how much they spend per ad impression. They also promise to create a lucrative market for all parties involved, including advertisers, ad agencies and cable programmers, as well as the cable operators themselves. Intelligent VOD/SDV Having utilized advanced video processing technologies and techniques to free up available throughput, operators will have sufficient space and an ideal architecture to add new, revenue-generating services. Through high density, multi-service video processing platforms, operators can increase their revenues through more personalized advertising opportunities.

In an SDV network environment, advanced video processing platforms offer the flexibility to be deployed either centrally at the primary video headend or regionally to address localized ad insertion and customization. The deployment of intelligent video processing technology can also effectively supplement today’s VOD servers and the current trend toward using baked-in VOD ads or pre-roll/post-roll ad playlists. In addition to providing a cost-effective mechanism for customizing high-quality, centrally produced video commercials for broadcast TV content, a multi-service video processing device can be used to dynamically overlay graphics and text onto the VOD content as well as provide other services, such as branding content with the local operator’s ID.

With the advent of more subscriber choice from the rollout of SDV-enhanced channel lineups and expanded VOD title catalogs also comes the opportunity for cable operators to increase revenue from zoned and targeted advertising. The SDV environment naturally lends itself to segmenting subscribers by groups, such as by zip code or neighborhood, and specific individual households or even specific subscribers. As in other parts of the network, the ad management portion has become more complex. Key to successful deployments are well-defined and standardized interfaces among the ad management, ad file storage servers and MPEG video splicing equipment used to enable these enhanced advertising applications, as well as a video processing system that can manage the complexity of information and activities. Standards and interfacing The cable industry has defined several key standards and ad management architectures that operators can leverage for increased management and control of ad presentations, such as SCTE 30 and SCTE 35. Compliance with these two standards has helped to ensure interoperability among equipment from vendors specializing in the MPEG video processing and content management areas.

A new ad management architecture being defined by the SCTE Digital Video Subcommittee as DVS/629 will enhance the industry’s current ad scheduler and trafficking and billing systems with well-defined functional entities, such as the ad manager (ADM) and the ad decision system (ADS), as well as define standards-based interfaces between devices. The ADM becomes the central point for managing and collecting the targeted insertion opportunities for video content (SDV, VOD, etc.). The ADS decides which ad to insert into each available slot in the video content, based on viewing profiles and habits, targeting information from other sources, and the other guidelines established by advertisers. The DVS/629 messaging protocol enhances the use of SCTE 30 and 35 messaging by standardizing the communication between the ADM and the ADS to coordinate the targeted insertion or personalized selection of ads or ad components, such as graphic or text overlays of the ad video stream. (See Figure 3.) The expected broad array of ad insertion capabilities, graphic and text overlays, content branding, interactive capabilities, or other service extensions argues for a high-performance video processing platform that provides a unified interface to the ad management system. The ability to support multiple ad delivery enhancements from a single, multi-function device simplifies operation, boosts manageability, and reduces capital and operational costs.

The era of addressable, on-demand video poses many challenges to existing architectures, technologies and business models. Multi-function, high-density video processing can help both in the recovery of requisite bandwidth and per-channel capacity and in the wimplementation of new advertising models. Highly targeted advertising services could enable operators to maintain or even increase that revenue stream. Kerry Washington is technical marketing manager for RGB Networks, and Jeff Tyre is senior product manager for RGB. Reach them at and

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