Next, let’s examine the contents of our example DVD, Planet Earth: North America. Because this DVD also supports the DVD-ROM format, we can open a Windows Explorer window, display the Folders side panel, and browse the contents of the inserted DVD. It’s helpful to go through this disc to give you an idea of what you might find in your own DVDs.
No matter which commercial DVD-ROM disc you look at, you’re likely to see a mess of files and directories. The Planet Earth: North America contents are shown in Figure 2-10. These include both DVD content and PC data files.
Only three of these folders are related to the DVD specification, and are of any use to set-top DVD players.
- VIDEO_TS
This is the entire playable DVD-Video content of the disc, including video and audio, menus, and navigation links. Everything else on the disc is auxiliary stuff.
- AUDIO_TS
This is an empty folder that is a placeholder for DVD-Audio content. DVDs can contain both DVD-Video and DVD-Audio content, so it is good form to include both folders on a disc, even if one is empty.
- JACKET_P
This folder contains the jacket picture content, which is optionally displayed by the DVD player when the DVD is inserted. This is a good idea defined in the DVD specification, but not used much in practice.
As mentioned earlier, the only useful folder here is the VIDEO_TS folder. The VIDEO_TS folder, shown in Figure 2-11, contains the playable DVD content, organized into separate units called video title sets (which is where the VIDEO_TS comes from). Note that each numbered file begins with the prefix VTS_. Title sets are an important organizing concept in the DVD specification: individual title sets contain material stored in the same format (i.e., standard or widescreen video), so the user can jump within the material without visible breaks.
The data for each title set is stored in three different types of files.
- VOB
The big files are called Video Objects (VOBs). A VOB contains the video and audio data as MPEG program streams, as well as associated navigational information. Some software applications can play VOB files directly, or split the video and audio streams out of them (if not encrypted). A large title set will be split across multiple VOB files.
- IFO, BUP
Smaller information (IFO) and backup (BUP) files containing menu and other information associated with accessing each title set.
Beyond the DVD-Video content, Planet Earth: North America also contains DVD-ROM content designed for access on a PC, including a number of computer data files at the root of the disc, plus some additional folders (see Figure 2-12) The top directory contains the standard AUTORUN.INF and the InterActual Player install.exe files, plus the common and win directories with installer data. All these files are ignored by DVD players. On a PC, however, inserting this disc will launch the InterActual Player application to access the WebDVD content provided with the disc.
The Images folder is a bonus added by Ralph LaBarge when he authored the disc. This contains hundreds of the NASA images used on the disc, conveniently preprocessed into three different sizes. That’s more than a CD’s worth of data, just tucked away as an added feature on the DVD disc.
Encore DVD and other authoring tools provide the ability to add a similar folder of data files to your discs.
We mentioned earlier that our example disc is compliant with the InterActual Player. So what exactly is that? Well, the InterActual Player (player.interactual.com) is a combination application that can be used as a DVD-Video player to play the content of the disc, or to access the DVD-ROM data on the disc. With this disc, we have an install.exe at the root of the DVD disc. This installs the player on your PC, along with disc-specific data.
The Planet Earth: North America disc has been authored to first offer the option of playing the disc, or accessing the DVD-ROM content images, as shown in the main DVD-ROM menu. The main DVD-ROM menu, shown in Figure 2-13, then describes the features of the disc.
For the moment, let’s ignore the player and look at the DVD-ROM content with the InterActual player. The InterActual Player is innovative in that it combines web-style text and graphics with video and audio from the DVD. With this DVD, each screen provides text information about that geographic region, displays slide images of the overall region, and plays video in a window with accompanying audio. See Figure 2-14.
Figure 2-14. The Planet Earth DVD-ROM content includes screens of information about geographic regions with accompanying video clips.
Various screens also include WebDVD links. These links (an example is shown in Figure 2-15) open a web browser to access more information on that mission from the NASA site.
Note
While the design of DVD menus and navigation is totally under the control of the DVD author, you will find many discs have a fairly consistent structure, at least in terms of the main menus. On the other hand, the DVD-ROM or WebDVD material included on commercial discs is wildly diverse. Some may provide an enhanced interface to the same content, as in the Planet Earth disc, while others may provide totally different material such as games or online references.