SAN JOSE, CALIF.—The FCC incentive auction is a game-changing opportunity for broadcasters. Many broadcasters look at channel sharing as a way to cash in on the spectrum auction and still remain on-air. However, stations considering channel sharing need to be aware of the technology challenges and solutions. This article provides insight into how channel-sharing stations can optimize encoding efficiency and video quality utilizing the latest tools in compression including distributed statistical multiplex (statmux) architectures.

KEY TECHNOLOGY CHALLENGES
A channel sharing agreement (CSA) can be between two or more duopolies, station groups or independents, and effectively allows the participating stations to distribute their programming over a shared amount of bandwidth. This pooled use of available spectrum offers a number of benefits, but also carries with it several technical challenges. One of the main issues is encoding efficiency. Broadcasters need to pack as many MPEG-2 channels as possible into the available 19.39-Mbps ATSC transport stream while maintaining their desired level of video quality.

Bitrate allocation can also be challenging, which is where statmuxing plays a critical role. To ensure that the requirements of a CSA are met, the participating channels must agree on how to distribute the bit-rate and video quality. Utilizing a constant bit-rate stream in a multiplex is not a viable option, as it would limit bandwidth efficiency and impact overall video quality.

Furthermore, many broadcasters want to combine their channels from geographically dispersed encoding feeds. But how do you maintain an encoder at one station when the statmuxing and transmission is happening across town—or perhaps across the country? Passing SDI circuits between the channel-sharing stations is an expensive proposition, so the solution needs to be both cost-effective and efficient while guaranteeing quality.

ADVANCED VIDEO COMPRESSION AND ANALYTICS TECHNOLOGY
As new video compression standards have been created over the last several years, they’ve essentially doubled encoding efficiency. These developments actually trickle down, so that coding techniques developed for both MPEG-4 AVC and HEVC also benefit MPEG-2. Statmux technology works hand in hand with AVC and HEVC tools and techniques to support the higher channel density required of CSAs.

Utilizing statistical multiplexing, stations can balance video quality across all of the channels in a statmux pool, shifting the bit-rate between those channels with low complexity statistics to those with more in real time. The VQ runs at its highest average when all sources in the pool are of a different content type: sports, sitcoms, talk shows, etc. There needs to be at least two channels of differing content in each to gain noticeable benefit.

A distributed statmux solution goes even further, allowing channel-sharing stations to build a single statmux pool from up to 32 geographically dispersed encoders. This capability further increases bandwidth efficiency, flexibility and cost savings, while enabling broadcasters to maintain high video quality.

For monitoring and measuring bit-rate allocation in the pool, video analytics software plays a crucial role in assuring that quality benchmarks are reached. Look for a solution that integrates seamlessly with the encoder to offer monitoring dashboards, real-time video degradation alarms, channel/pool quality comparisons, trend analysis, and a variety of reporting tools. These capabilities will enable broadcasters to achieve the highest possible video quality for their allocation, and to gauge the ultimate success of their CSA.

CONCLUSION
As the world leader in video delivery infrastructure, Harmonic offers Emmy Award-winning video compression, statistical multiplexing and video analytics solutions, enabling broadcasters to make a seamless migration to channel sharing and provide amazing video quality across all channels.