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DVB Update: DVD Authoring Systems

When the BBC aired its new interactive documentary series, “Walking with Beasts,” the company decided to develop a DVD that mirrored the broadcast, both in terms of visual quality and interactivity. This would allow the BBC to demonstrate and market the full concept before the program's air date.

A unique problem

Like most interactive programs on digital transmission platforms, “Walking with Beasts” requires that multiple audio/video streams be broadcast simultaneously. In this case, in addition to the ‘Original’ video program stream, there are four additional streams that make up the ‘Main Feature,’ ‘Facts,’ ‘Making Of’ and ‘Evidence’ interactive options.

Two of these streams also have alternative narration tracks. Although the episode runs for 30 minutes, in all there are two-and-a-half hours of video content being broadcast simultaneously, which the viewer can access at any point.

Of course, it is possible to replicate interactive functionality on DVD by using multi-angle features, which allow up to nine concurrent video streams, as well as clever programming to allow active highlight buttons. At each stage of the authoring process, the engineer must associate each of the angles (the audio and video assets) with a specific set of button commands. For a refresh rate of every two or three seconds (worst case delay before stream changing can occur), up to six buttons will appear on the screen that require the author to program an action. This ends up requiring as many as 9000 repetitive programming tasks for the 30-minute duration.

For an interactive section with four video angles and three interactive buttons per angle, to select from the alternate angles, combined with a stream change (refresh) rate of three seconds, typically would require three weeks of authoring. In order for the buttons to stay active, the sub-pictures need to be refreshed when switching angles, and as the user has the option of switching anywhere in the timeline, the refresh needs to be carried out at regular intervals.

The “Walking With Beasts” team, however, wanted a 30-minute per angle piece with five video angles and four to six interactive buttons in each angle to be delivered in just seven working days. This allowed an authoring window of just five days. Therefore, BBC Technology engineers set out to overcome the challenge of demonstrating multiple video streams on one screen, with full on-screen interactivity, while also cutting standard DVD production time by more than four weeks.

Additionally, the standard implementation on a multi-angle disc can be somewhat awkward, requiring end users to press the angle key on the remote control to select the desired stream by number. This almost always puts an unwanted, machine-generated icon on screen. What the BBC needed for this project was a close emulation of the interactive service, with the additional streams being selected by active menu buttons on the screen.


BBC Technology engineers knew that in order to meet their deadline, they would have to create a software program that eliminated the time involved with this particular phase of production. Having already researched this possibility for earlier company projects, the team began drawing up specifications for a customized software script to automate the repetitive programming tasks.

The development of this software required a fundamental understanding of the DVD specification and the most advanced authoring tool available from the Sonic Scenarist NT Professional system.

During the authoring phase, a Scenario file is generated that contains all the instructions about the data, including all the interactivity and subpicture (the interactive highlight) information. The Scenarist software allows the whole project file, including button commands and highlight information, to be exported as a text script file. Once exported, the engineer can opt to undergo the very complicated task of modifying the file.

This is where BBC Technology's custom script becomes a valuable addition to the process. The script is a utility that looks like a text editor and acts as an executable program file that repeats the menus at an interval rate the engineer chooses. The button commands are repeated, and the utility then goes back and modifies the subpicture and highlight repeats.

Because all the interactivity already is programmed, the utility essentially repeats these commands without error and at a much quicker rate than if done manually. Engineers using a significant amount of computer power can complete this phase of the authoring process in approximately 70 to 80 hours, instead of five weeks of manual programming. Once finished, the modified script file is then re-imported into Scenarist as a new Scenario file.


The immediate result was the production of an “interactive” disc that allows the BBC to demonstrate its interactive television service on an ordinary DVD player.

However, the software also represents a significant step forward for standard DVD production overall, making it possible for DVD producers to push the envelope in terms of creativity and functionality. Because the time involved with production is significantly reduced, programming engineers now can combine multi-angle features with complex interactive menus simply and easily, allowing viewers to seamlessly choose between camera angles and subject matter by navigating through on-screen prompts.

Julian Tow is group manager of BBC Technology — DVD & Multimedia. He can be reached