When you import video footage into iMovie, you may see black bars (or black space) on the top and bottom or the sides of the video image. This is normal. Digital video footage is recorded using standard ratios of width to height measurements, called the aspect ratio.
Standard definition video has an aspect ratio of 4:3, meaning for every four pixels of width, the frame has 3 pixels of height. A television screen has a 4:3 aspect ratio. Widescreen video has a 16:9 aspect ratio, meaning that the width of the frame is almost twice its height. Movie theaters have screens that can display this aspect ratio.
Depending on the aspect ratio of your footage (your camera may support both standard and widescreen formats), you may see one of the following black bar displays.
Black bars on the top and bottom (letterboxing)
If you see black bars on the top and bottom of your video image, your footage is being displayed in letterbox format. This happens when widescreen video footage (16:9 aspect ratio) is displayed on a 4:3 aspect ratio screen (like watching a widescreen DVD movie on a standard TV).
Black bars on both sides (pillarboxing)
If you see black bars on both sides of the video image, your footage is being displayed in pillarbox format. This happens when standard definition video footage (4:3 aspect ratio) is displayed on a 16:9 aspect ratio screen (like watching a standard definition broadcast on a widescreen HDTV).
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