Optimizing delivery of Authorware files from CDs

Introduction

Authorware pieces can be delivered from disks, local area networks, the Internet, and CDs. Due to their high storage capacity and low cost, CDs have become the medium of choice for distributing Authorware multimedia content rich with animations, audio, and video. However, the delivery of an Authorware piece from a CD may not be seamless and uninterrupted unless the user has optimized specifically for the CD. This TechNote offers several recommendations for optimizing Authorware pieces for CD delivery.

Planning ahead

Make several initial determinations about your project before burning your Authorware piece onto the CD. It is important to consider the target platform and the minimum speed of the CD-ROM drive needed to run the piece. Identify whether your piece is more linear or more interactive. Note which files will be used repeatedly and which files need to be accessed quickly. Verify whether your video and audio data streams are separate. Determine the general order your files will be accessed from the CD. Some of these initial decisions may influence:

Target Platform

Know ahead of time whether you are creating your Authorware piece for the Windows or Macintosh operating system. It is possible for both Windows and Macintosh computers to share the same Authorware files on one hybrid CD. Only the Authorware run-time application appropriate to the operating system viewing it will be visible to the user. To create hybrid CD disks, check the documentation that came with your CD-R mastering software.

Minimum CD-ROM Drive Speed

You will also want to determinethe minimum CD-ROM drive speed required to run your Authorware piece. CD-ROM drive speeds are advertised as 2X, 4X, 10X, and so on. Multiply the drive's speed by 150K/second to determine the data transfer rate for that drive. For example, a 4X drive will transfer up to 600K per second. However, be aware that other factors will impede the theoretical transfer rate for the intended minimum drive speed. (Remember that the components of the computer running the Authorware piece may also impede delivery. Other factors, such as CPU speed, available memory, disk fragmentation, and other bottlenecks may keep a CD-ROM drive from reaching its maximum data transfer rate. For more information on CD-ROM drive technology seeAndy McFadden's CD-Recordable FAQ.

Defining your CD project

The best strategy depends on the type of project being authored. A linear project is one where the user will access different files in a prescribed sequence. An interactive project would typically have a structure which allows the user to choose between following a sequence or jumping from one point to another. The initial navigation point (the introductory level which gives the user the options to view different materials) will be referred to as a"shell" in this TechNote.

Linear sequencing

If your program has groupings of material that are likely to be accessed in a linear fashion, then materials which will be viewed at about the same time should be housed in the same library. For instance, if the user will be moving through a series of chapters, then put all the materials (sound, graphics, text and so forth) associated with Chapter 1 in one library, all the materials associated with Chapter 2 in a separate library, and so on. Sometimes developers create libraries based on the types of material used in the Authorware piece (for example, all sounds in a sound library, graphics in a graphic library, and so on). Organizing the materials in this manner will cause the CD to jump back and forth between libraries to display the Authorware piece. Forcing the CD-ROM drive to search the CD from one end to the other for material will slow down the delivery of the files.

Varied or interactive organization

In more complicated situations, you will need to consider further optimization techniques beyond properly organizing libraries of materials. For convenience and clarity, a typical interactive situation will be described here and suggestions offered on how a developer could optimize the delivery of such Authorware files on the CD.

Example scenario

This interactive scenario is a book with 8 chapters. Each chapter has a 3-minute audio track, a 5-minute video clip, a text transcript of the audio, and a short multiple-choice quiz. The user can choose which chapters to view and in what sequence they are viewed, although most will view each chapter sequentially. The scenario would likely follow this order:

Installing CD files on the user's hard disk

The first optimization technique you will want to consider is installing some of the Authorware files onto the user's hard disk before running the piece. The computer displaying the Authorware piece will access material stored on the hard disk several times faster than material stored on a CD.

Good candidates for hard disk installation are files which require quick access or which are likely to be repeatedly accessed.

In the example above, it would be beneficial to install the shell of the program on the hard drive. The shell would include the main menu and the common interfaces in the chapters. The "wait screen" would also be installed on the hard drive, (this screen would appear while a new chapter is loading, to alert viewers that the program will resume shortly) because the file should appear quickly. The size of the files installed on the hard drive should be relatively small.

Even nonlinear projects may benefit from installing files on the user's hard drive. For instance, a developer might install all of the Authorware files except for video, sound, and graphics files. Another option would involve installing only the run-time application and Xtras, keeping all other files on the CD. For more information on the files required when installing your piece, seeWhich files you need to distribute and "Which files to include" in Authorware's Help.

Library organization within the interactive scenario

You can structure your project with all the media files that will be installed on the hard drive in one library. At installation time, the user can choose to copy the library to the hard drive (depending on the space available on the hard drive) and the speed the user desires. If you put 99% of your content into libraries, your Authorware code will be fairly small and can always be copied to the user's hard drive.

You should also set up your other libraries logically. In the example above, you would put all of your content (sound, graphics, text, and so forth) for each chapter in its own library. This helps keep files that are accessed in a linear fashion next to each other on the CD. Linear access is still important even in interactive scenarios because you can anticipate the path most users will follow.

Optimizing digital audio and video

Large digital video files should be left on the CD. The kind of video used and how the files are compressed will influence the delivery of your Authorware piece from the CD. Compress the video files for the data rate that matches your target platform (for example, double speed). Remember to use only 60% or less of the CD data transfer rate. Software programs like Adobe Premiere allow you to limit the data transfer rate for QuickTime video clips when run on a CD. Avoid displaying additional graphics from the CD while playing a video to minimize pauses during playback. This strategy also applies when playing back large audio files on the CD.

Use clean source video

As a rule of thumb, the cleaner the source video, the lower the data rate of your finished video. Always start with the best video source possible. Beta SP and HI-8 are examples of two high quality video formats. To prepare the video, do the following:

Assume that you want to target double-speed drives as the playback platform and Indeo is the codec used for compression. As a general rule, you should set the data rate to 200, key every 10 frames, interleave audio, and set the target for CD. Make sure to"flatten" QuickTime movies if they will be viewed on both Macintosh and Windows computers. To set these options, consult the documentation that came with your video-editing software.

Allow access to one data stream at a time

In each chapter in the above example, the user had the choice to hear the audio or see the video clip. The user is not provided with an option to play both at the same time. The user was given this choice because CD-ROM drives can transfer data most efficiently when the data is in one continuous file stream. If you have an audio track running from the CD and try to display a video clip from the CD at the same time, the audio could stutter or may stop completely. If you need to provide a soundtrack for your video, record it in the video file's audio track.

Arranging files on a CD

Another factor to consider when preparing data to be pressed onto a CD is file arrangement. Due to the manner in which data is read by a CD player, the location of a file on the CD is an important factor in determining how quickly that data can be accessed. Typically, files that are located toward the center of the disc are read faster than those at the outer edge. When media files that are used together are also close together on the CD, the time the CD-ROM drive spends moving between them is minimized.

To decide which files to place at the extreme inside and outside the disc, weigh the following:

To arrange the contents of your disc manually, you will need to copy the contents from your assembly hard disk into folders on a freshly formatted drive.

To manually transfer files from the hard drive to the CD

Note:Most optimization utilities place the applications at the beginning of the CD and the data files at the end of the CD. Because the end of the CD is toward the outer edge, this layout can result in the CD-ROM drive engaging in repeated full stroke seeks (moving from the center to outer edge of the disc). An Authorware piece running on a CD with this configuration may have serious performance problems.