There are several methods for producing a reduced-size movie from your composition, each with tradeoffs between speed and quality:

Nest the composition

Create a new composition at the smaller dimensions, and nest the large composition inside it. For example, if you create a 640 x 480 composition, place it in a 320 x 240 composition. Use the Fit To Comp command to scale the composition to fit the new smaller composition size: Press Ctrl+Alt+F (Windows) or Command+Option+F (Mac OS), and then collapse transformations by choosing Layer > Switches > Collapse. The resulting composition rendered at full resolution and best quality will have excellent image quality, better than if you had rendered using a reduced resolution.

Stretch the composition

This method produces the highest quality reduced-size movie but is slower than nesting. For example, if you create a 640 x 480 composition and render it at full resolution, you can set the stretch value in the Output Module Settings dialog box to 50% to create a 320 x 240 movie. For a composition rendered at full resolution, the image quality is excellent when the Stretch Quality is set to High.

Note: Do not use stretching to change the vertical dimensions of a movie when field rendering is on. Stretching vertically mixes the field order, which distorts motion. Use either cropping or composition nesting if you need to vertically resize a field-rendered movie.

Crop the composition

This method is ideal for reducing the size of a movie by a few pixels. Use the Crop options in the Output Module Settings dialog box. Remember that cropping cuts off part of the movie, so objects centered in the composition may not appear centered unless the movie is cropped evenly on opposite edges.

Crop to a region of interest

To render just a portion of the composition frame, define a region of interest in the Composition panel. Then, select the Region Of Interest option in the Output Module Settings dialog box before rendering. (See Work with the region of interest.)

Note: Cropping an odd number of pixels from the top of a field-rendered movie reverses the field order. For example, if you crop one row of pixels from the top of a movie with Upper Field First field rendering, the field-rendering order then becomes Lower Field First. Remember that if you crop pixels from the top of the movie, you need to add to the bottom row of the movie to maintain the original size. If you are willing to lose one scan line, this gives you a way to output two movies from one render, each with a different field order.

Render the composition at a reduced resolution

This is the fastest method to create reduced-size movies. For example, if you create a 640 x 480 composition, you can set the composition resolution to one half, reducing the size of the rendered composition to 320 x 240. You can then create movies or images at this size. Note that the reduced resolution reduces the sharpness of the image and is best used for creating preview or draft movies.

Note: When rendering at reduced resolution, set the quality of the composition to Draft. Rendering at Best quality while reducing resolution does not produce a clean image and takes longer to render than rendering at Draft quality.