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Scopus' DPI system

May 1, 2007 12:00 PM, BY MICHAEL ACER

Local ad insertion has long been a method used by television networks and service providers to supplement revenues. It allows them to combine national programming with local advertising, thus profiting from airing commercials for local businesses.

The growth of digital television content via satellite and cable transmission has brought about the need for ad insertion into digital programs. Digital program insertion can enhance the potential for additional income if done effectively. On top of performing ad insertion, digital program insertion allows network operators to switch programs seamlessly, as in moving from a national feed to a local feed, for example.

Digital satellite and cable systems deliver an ever-growing number of channels to their viewers. Increasingly, this content is compressed and sent to digital set-top boxes (STBs) in homes.

These systems require broadcasters to use digital turnaround solutions, which remove a digital program from a national source and add it to a multichannel, digital multiplexed stream — digital in to digital out. Digital turnaround-based systems can benefit from using digital program insertion (DPI).

Ad insertion techniques

Ad insertion products are comprehensive systems that integrate several different components including storage devices, a compression system, scheduling programs, distribution networks and a switcher/splicer. (See Figure 1.)

Figure 1.

Storage is the central component in an ad insertion system. Ads are stored in videotape banks in analog format or in video servers in digital form after being compressed using, for example, the MPEG standard. The server receives new programming and advertising content from such sources as tapes, encoders, compressed files on DVDs, or from the distribution network.

The digital compression system consists of encoders that compress the ads to high-quality constant bit rate (CBR) MPEG files for storage and playback. Scheduling systems create the time controls for the ad or clip database, arrange the ads on the server, build ad packages, and remap the outputs from the video server. Billing and management functions may also be included with scheduling. Contribution is performed through the master headend by file transfer over an existing network. This process is necessary for distributing the compressed ads or programs to several sites.

When both the original program and stored ads are in analog TV format, a standard switch can function as the splicer. Selecting between the incoming program and the stored ads is predetermined. The switch becomes a multiplexing unit with splicing capabilities for digital TV services. The splicing of MPEG streams allows local ads to be inserted into digital programming seamlessly and assures smooth and uninterrupted delivery of the content.

Analog ad insertion

Original ad insertion systems operated solely on analog programs and ads. National feeds would sometimes include gaps into which local ads were to be dubbed. The splicer would switch, at predetermined times, from the national content to local ads or programming. Automated analog playout systems included cue tones in the original content, such as a movie, to indicate the points of insertion for ads. These audio cue tones were used to trigger insertion into the network feed with a video switch.

When television networks and service providers started transmitting digital compressed programming, local content insertion still used analog methods. In the analog workflow, incoming MPEG-2 content is decoded back to analog formats (NTSC, PAL).

The local content, if stored digitally, is also converted to analog and inserted into the output stream. Systems that transmit digital content to the user's home would require that the modified program be encoded again to MPEG. Most ad insertion solutions available today use analog insertion techniques. (See Figure 2.)

Figure 2.

Though this process is effective for local content replacement, it is problematic. The process of two encoding/decoding passes can degrade overall video quality.

MPEG is a lossy compression system that deletes unnecessary information the human eye does not see. Multiple encoding and decoding may remove too much information, causing visual artifacts.

A more important issue to the provider is that analog insertion in a digital system is a very expensive process. Multiple decoders and an encoder may be required to create the system, which thus requires increased time and labor for system configuration and management.