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Chapter 20: Performance and memory
Memory
Memory usage
Memory requirements for viewing and rendering increase with the resolution of the composition frame, the memory
requirement of the most memory-intensive layer in the composition, and the size of the project file.
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 compo-
sition. 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
resolution than 2 layers at motion-picture film resolution.
When a layer includes a composition as a source item, everything in that composition must be rendered before the
next layer is rendered.
The memory requirements of a layer increase under the following circumstances:
•
You use a larger source image.
•
You add a mask.
•
You use certain blending modes or effects, especially those that involve multiple layers.
•
You apply certain output options, such as 3:2 pulldown, cropping, and stretching.
•
You add shadows or depth-of-field effects.
If you have no problems viewing each frame of a full-resolution, best-quality preview of a composition, then you
have enough memory to render the composition. Rendering a composition into a movie takes no more memory than
displaying it on-screen.
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, follow procedures in this section to free memory or reduce
the memory requirements of your most memory-intensive layers, and then try again.
Free memory immediately with one or more of the commands in the Edit > Purge menu.
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
Note:
The value 2,097,152 is a conversion factor that accounts for the number of bytes per megabyte (2
20
), the number
of bits per byte (8), and the number of channels per pixel (4).
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.
Summary of Contents for AFTER EFFECTS 7.0
Page 1: ...Chapter 1 User Guide...
