How Do You Change Composition Dimensions in After Effects?

You change the composition dimensions in After Effects by adjusting the Width and Height settings within the Composition Settings dialog box. Here's a detailed breakdown:

Accessing Composition Settings

1. Select the Composition: In the Project panel or Timeline panel, select the composition you want to modify.
2. Open Composition Settings: There are a few ways to access the Composition Settings:
   • Go to Composition > Composition Settings in the top menu bar.
   • Right-click on the composition in the Project panel and select Composition Settings.
   • Use the keyboard shortcut: Ctrl+K (Windows) or Cmd+K (macOS).

Modifying Dimensions

1. Locate the Width and Height Fields: In the Composition Settings dialog box, find the "Width" and "Height" fields under the "Basic" tab. These fields display the current dimensions of your composition in pixels.
2. Enter New Values: Click in the "Width" and "Height" fields and enter the desired pixel values for your new composition dimensions.
3. Lock Aspect Ratio (Optional): If you want to maintain the current aspect ratio while changing the dimensions, make sure the "Lock Aspect Ratio" button (usually a chain icon) is enabled between the Width and Height fields. When locked, changing one value will automatically update the other proportionally.
4. Click OK: Once you've entered the new dimensions, click the "OK" button to apply the changes.

Important Considerations

• Content Scaling: Changing the composition dimensions will not automatically resize or reposition any existing layers within your composition. You may need to manually adjust the scale, position, and other properties of your layers to fit the new dimensions. Consider pre-composing the content before rescaling if you want to maintain the original resolution.
• Pixel Aspect Ratio: Be mindful of the Pixel Aspect Ratio setting in the Composition Settings. Changing the dimensions while using a non-square pixel aspect ratio can lead to unexpected distortions. Square pixels (1.0) are generally preferred for web and most modern video formats.
• Composition Presets: If you're working with a standard video format (e.g., 1920x1080, 4K), you can choose a preset from the "Preset" dropdown menu in the Composition Settings. This will automatically set the Width, Height, Pixel Aspect Ratio, and Frame Rate for that format.
• Nested Compositions: When you change the dimensions of a composition that is used as a layer within another composition (a nested composition), the nested composition will automatically update in the parent composition. However, as with regular layers, you may need to adjust the scale or position of the nested composition layer to fit the parent composition's frame.

Example Scenario

Let's say you have a composition that's currently 1280x720 pixels, and you want to resize it to 1920x1080 pixels (Full HD). You would:

1. Select the composition.
2. Open Composition Settings (Ctrl+K or Cmd+K).
3. In the Composition Settings, change the "Width" field to 1920 and the "Height" field to 1080.
4. Click "OK."
5. Review the layers in your composition and adjust their scale and position as needed to fill the new frame.

By following these steps, you can easily change the dimensions of your compositions in After Effects. Remember to always check and adjust your layers after resizing to ensure they are properly positioned and scaled within the new frame.