Calculating Other Allowances
There are several other factors that should be taken into account when determining
available disc space.
• Slideshows: Each still in a slideshow requires approximately 200 kilobytes (KB) of disc
space. A full slideshow with 99 stills requires about 20 MB of disc space. If the slideshow
contains audio, you will find that the audio can require as much or more disc space
than the stills. If your disc contains many stills, you will need to take them into account.
• Still menus: Each standard still menu requires about 300 KB of space, depending on
the number of buttons.
Layered menus can require a lot more space than standard menus because a new menu
is created for each button in each of its separately specified states (normal, selected,
and activated). This can mean as many as 12 menus are created to support 4 buttons.
Creating Menus Using the Layered Method
for more information on layered menus.
Note: Menus that use button shapes with motion assets assigned are considered to
be motion menus, and need to count as a video asset.
Calculating Disc Space Requirements
• Subtitles: The amount of space required by subtitles can vary widely, depending on
how many of the 32 streams you use, the type of content you use (simple text characters
or full-screen graphics), and how often you change them (several times a second, or
more typically, once every four or five seconds).
Simple subtitles average about 10 kbps—roughly 2 megabits of space per hour, which
is negligible on most titles. If you intend to use subtitles more as an animation tool,
with full-screen graphics that change often, you must make significant allowances for
them. (The maximum bit rate allowed for a subtitle stream is 3.36 Mbps—almost as
much as the video stream.)
• Transitions: The amount of disc space required by each transition varies depending on
the transition’s length and type. In general, for SD projects, which use a bit rate of
6 Mbps for transitions, you should allow 750 KB of disc space for every second of
transition time in the project. For HD projects, which use a bit rate of 20 Mbps for
transitions, you should allow 2.5 MB of disc space per second.
Note: Keep in mind that adding a transition to a menu results in a separate transition
clip for each button—a menu with 18 buttons can require 18 transition clips.
Unless you are using an exceptional number of stills, menus, or subtitles, you can usually
account for the amount of space required by these items by allowing a five percent
overhead. The easy way to apply this overhead amount is to multiply the bit rate you
have figured out by 0.95. In the earlier example, the DVD-5 disc bit rate drops from
3.77 Mbps to 3.58 Mbps; the DVD-9 bit rate drops from 7.65 Mbps to 7.27 Mbps.
It is much better to be conservative and find yourself with some disc space
left over than to get to the end of the project and find it will not fit on the disc.