> Configuring Export Dimensions
> Use the dimensions options (Figure 68) to set the frame size of your exported video. You should not set a size larger than your canvas size—it does not improve image quality.
> Figure 68. Export Settings Dimension Options
> Set these options, as described in Table 18. When you’re done, click OK.

> Table 18. Dimensions Settings
> Control | Description
> Scale by | Select to scale your video by a percentage. This shrinks the frame proportionally, preserving the aspect ratio.
> Scale to custom size | Select to specify the width and height of your exported video.
> Letterbox Content | Check to process for letter boxing. Letter boxing preserves the aspect ratio of the original canvas size by placing black bars at the top and bottom (or the sides), where there would be blank areas created by a custom size with a different aspect ratio