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 3 GB is actually available to the foreground application, because Mac OS X uses approximately 500 MB 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 General Specialist website.) After Effects on 64-bit Windows operating systems can use up to 4 GB of RAM with no special configuration.

Memory requirements for rendering (either for previews or for final output) increase with the resolution of the composition frame and the memory requirement of the most memory-intensive layer in the composition.

After Effects renders each frame of a composition one layer at a time. For this reason, the memory requirement of each individual layer is more important than the duration of the composition or the number of layers in the composition. The memory requirement for a composition is equivalent to the memory requirement for the most memory-intensive single layer in the composition. For example, it generally takes less memory to render 30 layers at NTSC dimensions than 2 layers at motion-picture film dimensions.

If you have no problems previewing each frame of a full-resolution, best-quality preview of a composition, then you have enough RAM to render the composition for final output.

The memory requirements of a layer increase under the following circumstances:

• Using a larger source image

• Enabling color management

• Adding a mask

• Adding per-character 3D properties

• Using certain blending modes, layer styles, or effects, especially those involving multiple layers

• Applying certain output options, such as 3:2 pulldown, cropping, and stretching

• Adding shadows or depth-of-field effects when using 3D layers

After Effects requires a contiguous block of memory to store each frame; it cannot store a frame in pieces in fragmented memory.

Use the following formula to determine the number of megabytes required to store one uncompressed frame at full resolution:

(height in pixels) x (width in pixels) x (number of bits per channel) / 2,097,152

For example, a DV NTSC frame in an 8-bpc project requires 1.3 megabytes, and a D1/DV PAL frame in an 8-bpc project requires 1.6 megabytes, whereas a 1080i60 DVCPRO HD frame in a 32-bpc project requires 21.1 megabytes.

Occasionally, After Effects may display an alert message indicating that it requires more memory to display or render a composition. If you receive an out-of-memory alert, free memory or reduce the memory requirements of the most memory-intensive layers, and then try again.

Free memory immediately with one or more of the commands in the Edit > Purge menu.

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 required to store your final output movie. However, such a calculation can give you a rough idea of the maximum storage space you may 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 storage requirement 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.