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Graphics Insertion In The DVB-ASI Stream - TvTechnology

Graphics Insertion In The DVB-ASI Stream

Graphics content in the broadcast stream is becoming increasingly prevalent throughout the world as traditional broadcasters compete with the infocasting of the Internet. Graphics content is also used to promote and brand a channel, and may provide additional sources of revenue both as sponsored information broadcasting (weather, sports scores, stock market values, school closings, and local information) and interactive content (for example, call a number to order a product featured in a show).
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Graphics content in the broadcast stream is becoming increasingly prevalent throughout the world as traditional broadcasters compete with the infocasting of the Internet. Graphics content is also used to promote and brand a channel, and may provide additional sources of revenue both as sponsored information broadcasting (weather, sports scores, stock market values, school closings, and local information) and interactive content (for example, call a number to order a product featured in a show).

Whilst there are a large number of graphics devices available to produce the graphic content, ranging in price from a few thousand dollars to tens of thousands of dollars, most of these devices operate in baseband, i.e. the uncompressed world of serial digital or analog video. The branding or other graphics content is applied in production or master control just prior to uplink or encode for transmission, whether via satellite, terrestrial transmitter, or cable. The graphics content is common to every receiver within range and it is not possible to localize the content for a community area.

Yet there are many opportunities presented by providing more localized graphics content, whether for information, advertising, local branding, or interactive television. The problem is that local distribution, usually via cable headends, does not bring the video signal down to baseband but deals directly with the digitally encoded information, most likely in MPEG format. Hence, traditional graphics devices like character generators cannot be used, because they operate with uncompressed video signals. It is too expensive to decode the video stream to baseband, apply the graphics, and re-encode. The other problem with bringing the video stream back to baseband and re-encoding is that it may introduce artifacts and degrade the picture quality.

The MPEG Domain

MPEG encodes and dramatically compresses SD video, from 270 Mbps down to 6 Mbps or lower. The compression is achieved by removing information that the eye is not particularly sensitive to. MPEG reduces the number of colors and encodes frames into sequences by storing only the changes from one video frame to the next. The MPEG data is transported in a stream, usually a DVB-ASI stream. The DVB-ASI standard allows interconnection of systems from different vendors, using the same cabling and routing infrastructure as existing 270 Mbps SDI equipment. The 270 Mbps ASI stream can carry a Multi-Program Transport Stream (MPTS) with multiple program channels, each with different varying bit rates.
To address this potential new graphics market, Pixel Power is developing an ASI stream character generator, which inserts graphics content directly into the encoded MPEG stream within the DVB-ASI multiplex. The concept is to extract the required MPEG stream from the multiplex and dynamically overlay the graphics, outputting a locally branded DVB-ASI stream, at the same time taking care not to degrade the picture quality.

There are a number of basic graphics insertion devices that do this, but they are limited to static logo insertion or simple scroll movement and do not offer the rich functionality and feature set of a character generator broadcast graphics device. Pixel Power considered that local graphics content should be possible with the same range of effects, animations, transparency, and text quality as a broadcast graphics device used for primetime television.

Key features for primetime graphics are linear keying, transparency, animation, audio, and multiple layers and regions. Such capabilities create the subtle and sophisticated graphics look that dominates the major networks. Each of these features creates its own set of problems when working in the MPEG domain, and this is largely why the existing MPEG stream graphics insertion devices do not offer rich graphics functionality.

Advanced Graphics

Linear keying and transparency require that the overlaid graphics be mixed with the underlying video signal, rather than simply replacing it. The mixing process in Pixel Power graphics equipment is additive, so that when a white graphic is keyed on a white object there are no black edges visible. Such a mixing process is also fundamental in implementing transitions between graphics, such as fades or wipes.

Animation takes many forms, from a simple animated logo in one corner of the screen to full frame animated backgrounds. Then there is animation of the graphic elements themselves, both 2D and 3D. Pixel Power equipment offers keyframe-based and preset animations which can be applied to text, pictures, and video clips.

Multiple layers and regions allow a large amount of information to be presented in a full screen, which might include a squeezed back window of the main program or an inserted video clip, surrounded by panels displaying weather information, sports scores, tickers covering stock values, and breaking news stories. The regions have to be rendered independently and then mixed together, before overlaying the original MPEG stream. Finally, the resulting new MPEG stream is inserted back into the DVB-ASI multiplex.


In addition to the richness of graphics capabilities, the other main difference between a broadcast CG device and a basic stream inserter is the ability to interface to data sources and complex automation systems. The traditional logo inserter operates autonomously, displaying logos stored locally and the only information it receives from outside is which logo to display and when to bring it on and off. The broadcast character generator, in contrast, can generally interface to a wide range of data sources and automation systems for displaying dynamic content automatically. Such functionality is built in to the Pixel Power ASI stream CG and includes links to databases and spreadsheets, as well as a dedicated XML control protocol supported by most automation and content providers. It is also possible to take data and control information directly from the data packets in an ASI stream, allowing central control of localized content.

For example, Quest Research uses Pixel Power Clarity systems to implement automated master control graphics for sports, news, stock market information, weather alerts, and school closing information. The ability to deliver such content at the cable headend in the DVB-ASI stream allows it to be localized further.

The Pixel Power ASI stream CG is based on the existing Clarity100 feature set and includes functionality such as clip playback, text animation, multiple ticker support with automated data sources, cell animation, and audio group mix capability. It uses proprietary technology to insert high quality graphics in the ASI stream without the attendant degradation and expense of a full MPEG decode/encode process.