Close captions, or subtitles, help to describe the action or dialogue in a video. They work well in situations where the movie's native text is illegible or the events in the video are unclear. And if you'd like to add close captions to a video on your Mac computer, you can take advantage of the titling feature in the Mac native iMovie application and hard code subtitles to your videos.
Launch iMovie. Click on the "Timeline View" button beneath the program's preview window. Drag and drop the video file into the timeline window at the bottom of iMovie -- the video will be laid out in a series of key frames.
Select the portion of your video that you'd like to close caption. Hold down the left button on your mouse, while dragging your cursor across the desired portion.
Click on the "Titles" button above the timeline. Type the desired text into the fields at the bottom of the Titles menu. Click on the "Color" box to select a text color from iMovie's color palette.
Click on the drop-down box in the Titles menu to select a font for your text. Drag the "Size" slider to the left to decrease the size of your captions. Drag the slider to the right to increase their size.
Click on the "Update" button in the Titles menu to add your captions to your video. Select the "Share" option from iMovie's File heading. Select the "Quicktime" option in the Share menu, and then click " Share" to render and export your movie.