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Featured CED VideoDisc No. 7 - Winter 1998

A Walk Through the Universe (Interactive)

This CED, an interactive introduction to astronomy by CBS, in my estimation makes the most effective use of the interactive features available on the RCA 400-series players like the SJT400 shown in the photo. Unfortunately, this title was a demonstration disc distributed only to libraries and educational institutions, and thus will be difficult to find. Interactive discs were designed for viewing in a random access fashion; i.e. the user could view the material on the discs in any sequence desired using the 30-button remote control, and no two people would necessarily view a disc in the same sequence. This is in contrast to the vast majority of CED's which were intended for linear viewing from the beginning to the end of play time.

Notice in the photo that the TV is showing the disc's main menu, while the minute counter on the player indicates the mechanism is 30 minutes into the disc play time. It actually makes sense to put the main menu half-way through the disc play time, as the time needed to locate any section of the disc from the menu will be minimized. After loading this disc, the user sees a brief intro, followed by a stop page prompting the user to go to BAND 33. A stop page is a specially mastered groove on the disc causing the player's pickup arm to halt, where all four video frames have identical content to eliminate on-screen jitter. After using the remote to advance the player to BAND 33, the user sees another stop page showing the main menu. From there, the remote is used to navigate through a hierarchical set of menus in any order desired. The remote can also be used to program band sequences (maximum of five bands), which on this disc were used to summarize the disc contents. On the two Vidmax murder/mystery discs, band sequences were used to create sixteen different scenarios with different outcomes from the video sequences on a single disc.

It is possible to view interactive discs on any CED player, but on models other than the 400-series, the results will be more or less nonsensical. This is because these players have no means of recognizing stop pages, and will play right through them with the image being visible for just a fraction of a second. This wouldn't be too bad on "A Walk Through the Universe," since the content of each band can still be understood, but would be a shambles on the murder/mystery discs as some bands would present contradictory information and only certain band sequences make sense. "The Life and Work of Michelangelo" is the one interactive title that can be adequately viewed on any CED player, as it contains no stop pages. This disc is arguably not really interactive, but it contains very slow scans of art masterpieces that usually can be frozen on screen without jitter by pressing the PAGE key.

The 30-button remote included with the SJT400 and SKT400 has several buttons concerned with interactive operation as summarized below. More complete details are available in the SKT400 Owner's Manual.

BAND- Used to enter a band (program segment) for the player to start at. Discs can have up to 62 bands per side.

PAGE- First press to freeze disc play, second press to enter a page number in the format minutes:seconds:sixtieths of seconds.

TIME- Used to enter a start time for the player to begin play at in the format minutes:seconds.

PROG- Used to program a start and stop time sequence or a band sequence (up to five bands).

SEEK- Initiates BAND, PAGE, and TIME entries after they are keyed in.

PREV- Locates and stops at the previous stop page on interactive discs.

NEXT- Locates and stops at the next stop page on interactive discs.

PLAY- Used to initiate a play sequence that immediately follows a stop page.

A common mistake in page mode is to press NEXT instead of PLAY after viewing the last stop page in a sequence. This causes the player to begin seeking the next stop page at normal play speed, but though video is visible, audio is muted. To correct this, immediately press PREV to go back to the stop page, then press play. Audio is muted to eliminate static sounds while the player is in page mode.

In theory, one side of a videodisc can contain 27,000 individual pages (one for each groove assuming a sixty minute length). If RCA had ever introduced their canceled industrial player, that number could have gone up to 108,000 images as that player was to have a digital frame buffer to display individual frames with the stylus lifted from the disc. In practice, these large storage capacities would never have materialized as every groove on the disc would have to be perfect for them to be played back entirely. RCA's interactive guidelines recommended programming six consecutive grooves for each stop page, yielding 4,500 still images possible per disc side. This way, a groove could be damaged and the stylus would simply jump over to the next groove and display the still image. "Space Shuttle- Mission Reports" makes the most extensive use of still images, containing several hundred that are all indexed in the booklet enclosed with the disc.

RCA introduced the interactive players and discs just a few months before player production was canceled, so only seven interactive titles were released for retail sale. These all came from RCA, and were each enclosed in a box. The following table lists these discs in stock number order, which corresponds to release order, and also details any inserts included in the box with the disc. In general, the later titles are less common. "The Entertainment Game" and "Space Shuttle- Mission Reports" are particularly difficult to find.

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