Ram and disk caches, Memory & cache preferences – Adobe After Effects CS3 User Manual
Page 44
AFTER EFFECTS CS3
User Guide
39
The operating system imposes certain limits on the amount of memory that an application can use. After Effects on
the Mac OS X operating system can use up to 3.5 GB of RAM, although only about 3GB is actually available to the
foreground application, because Mac OS X uses approximately 500MB to load the user interface libraries. After
Effects on 32-bit Windows operating systems can use up to 3 GB of RAM; however, to use more than 2 GB in After
Effects, you must configure Windows XP or Windows Vista appropriately. (For details, see the Microsoft website or
Jonas Hummelstrand’s website:
.) After Effects on 64-bit Windows
operating systems can use up to 4 GB of RAM with no special configuration.
Note: These numbers are for each After Effects process. The background processes used to render multiple frames simul-
taneously can each use the amount of RAM mentioned above. (See “Render multiple frames simultaneously” on
page 40.)
Because video is typically compressed during encoding when you render to final output, you can’t just multiply the
amount of memory required for a single frame by the frame rate and composition duration to determine the amount
of disk space needed to store your final output movie. However, such a calculation can give you a rough idea of the
maximum storage space you might need. For example, one second of uncompressed standard-definition 8-bpc video
requires approximately 40 megabytes (MB). A feature-length movie at that data rate would require more than 200
GB to store. Even with DV compression, which reduces file size to 3.6 MB per second of video, this translates to more
than 20 GB for a typical feature-length movie. It is not unusual for a feature-film project—with its higher color bit
depth and greater frame size—to require terabytes of storage for footage and rendered output movies.
RAM and disk caches
As you work on a composition, After Effects temporarily stores some rendered frames and source images in RAM,
so that previewing and editing can occur more quickly. After Effects does not cache frames that require little time to
render. Frames remain uncompressed in the cache. You can control how After Effects stores images by setting image-
caching preferences.
After Effects also caches at the footage and layer level for faster previews; layers that have been modified are rendered
during the preview, and unmodified layers are displayed from the cache.
Blue bars in the Timeline panel mark frames that are cached to disk. Green bars mark frames that are cached to RAM.
Choose Show Cache Indicators from the Timeline panel menu to turn the cache indicators on and off. Showing the
cache indicactors decreases performance slightly.
When the cache is full, any new frame added to the cache replaces a frame cached earlier. When After Effects renders
frames for RAM previews, it stops adding frames to the cache when the cache is full and begins playing only the
frames that could fit in the cache. The disk cache is not used for RAM previews. If disk caching is enabled, After
Effects can store rendered items to your hard disk when the RAM cache is full during standard previews.
The RAM cache and disk cache are automatically purged when you quit After Effects.
To purge the RAM cache and disk cache, choose Edit > Purge > Image Caches.
Memory & Cache preferences
Set memory and caching preferences by choosing Edit > Preferences > Memory & Cache (Windows) or After
Effects > Preferences > Memory & Cache (Mac OS).
For information on the Conformed Media Cache preferences, see “Work with the media cache” on page 67.
Maximum Memory Usage
The maximum amount of memory that After Effects can use to render a single frame.
This preference is only relevant during rendering, either for previews or for final output. When After Effects is not