Digital program insertion
By Wayne Sheldrick
As the transition from analog to digital broadcasting continues, more and more traditional applications must be converted to take advantage of the new digital medium. One of these applications is the insertion of local advertising content into the program service at cable headends – a multibillion dollar revenue generator for cable operators.
Figure 1. In the DPI system shown above, local advertising is encoded and sent to the local headend, which uses a bit splicer to insert the advertisement at the desired point in the network’s programming.
Digital program insertion (DPI) capability offers a much higher degree of security, increased regional control of program insertion and enhanced management of other crucial digital server-based applications. A digital program/commercial insertion system is shown in Figure 1.
The traditional analog method sends cue tones along with the video that trigger a tape machine to start or stop playing an advertisement. A simple video switch is triggered to perform a transition between the two sources. The headend is permitted to insert its own advertising at times made available by the program provider, commonly known as “local avails.” This procedure is by nature slow, insecure and offers little localized control.
In digital operations, programmers and cable operators must be able to handle this process digitally, or risk losing huge amounts of potential ad revenue. Digital offers several advantages and provides an opportunity to expand the functionality of the cueing mechanism.
Today’s digital technology provides a method for inserting any program content into an existing service in real-time. Programmers and cable operators are moving quickly to take advantage of this new technology. The Lifetime Movie Network is currently conducting DPI trials across the United States to verify operation of systems by various server/splicer vendors. The DPI technology is installed as an overlay to the existing cue-tone system, which allows the use of both analog and digital ad insertion during the transition period. In addition to compressing the signals, the encoder injects DPI signaling based on cue trigger inputs.
Advantages of digital
DPI has the ability to eliminate many of the shortcomings of analog. But, for DPI to be effective, the splice points where ads are inserted must be identifiable. A switching system can then be used to control the airing of content from servers and other sources.
An SCTE ad hoc committee developed a standard, SCTE35 2001 (DVS 253), to define the trigger to signal the local video server to play an ad, as well as SCTE30 2001 (DVS 380), standardizing the application programming interface (API) between servers and splicers. Typically these devices will be supplied by different companies, so a standard method of communication is required.
The API is based on an Ethernet TCP/IP connection, and allows for the setup and teardown of network connections. Each connection controls one insertion channel from a server, so there may be multiple connections open at any one time. The protocol is also expandable, so that one or more splicers could have connections to one or more servers simultaneously.
The protocol is primarily designed for use with a splice info message, but it could also be used for local control of a server, for example, in VOD applications.
While the primary goal was to allow the local insertion of ad content at a cable headend, the SCTE group also worked to remove restrictions that would keep the standard from being used for any programming and within any MPEG-compliant system, such as DVB or ATSC.
A critical component of successful program insertion is accurate splice timing. Various methods can be used to signal a splice point in an arbitrary video stream, and to signal a video server to start playing content to replace the network feed.
This splice insert command references timing information found in the video stream. However, even a digital video file server requires some time in advance of a splice point to cue up frames of video.
Therefore, a splice insert command is sent at least once and at least four seconds before a splice point. The same splice insert command may be sent multiple times to guarantee successful reception. DPI offers the ability to schedule ad insertions far in advance and ensures that the ads are placed in the correct order, at the proper times. These enhancements are made possible through the Splice Information section. This area is composed of a start command, a stop command and a cancel command.
Both the start and stop commands can be signaled to activate immediately upon reception, or to activate at some time in the future. A cancel command always occurs immediately, and terminates the current insert or any cued splice point. The stop command is optional, since the ad will end when the end of the stored content is reached.
This implementation provides two key features that are unavailable with analog cue tones: scheduling of avails well into the future, and the establishment of different groups of splice insert commands for the same avail period. This is more effective than sending multiple cue-tone sequences at the same time, as is done in analog. Because these commands are sent in advance and transmitted faster than analog tones, the accuracy of the splice points is retained.
The other information related to the splice includes the unique program ID, the total number of avail periods and the specific avail period this event is referencing. This data provides better control over scheduling and allows the DPI system to automatically recover from missed events. For security, the splice information section supports a simple fixed-key encryption mechanism.
Thanks to improved technology and industry standards, digital program insertion offers tremendous revenue potential for cable operators, with greater capability for targeted advertising and faster, more efficient, secure ad insertion. As operators roll out additional advanced services such as VOD, they will reap even more benefits from the superior switching and control ability of DPI systems.
Wayne Sheldrick is principal engineer for Scientific-Atlanta.
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