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Aspect ratio of video files:
nuts and bolts

Focus on Aspect Ratio

What is aspect ratio?

According to Wikipedia, the aspect ratio of an image is the ratio of the width of an image to its height, expressed as two numbers separated by a colon, e.g. x:y (pronounced “x-to-y”).

The most common video aspect ratios are 4:3 and 16:9.

  1. The 4:3 ratio for standard television has been in use since television’s origins and many computer monitors employ the same aspect ratio.
  2. 16:9 is the international standard format for HDTV, non-HD digital television, and analog widescreen television.

These aspect ratios can be easily distinguished. 4:3 has a more “square” format, while 16:9 is more “rectangular” (See Figure 1).

Comparing 4:3 and 16:9 aspect ratios

Figure 1: Comparing the two most popular aspect ratios

It should be noted that the 16:9 aspect ratio is considered to be more aesthetically pleasing and closer to the way we humans naturally perceive images. This aspect ratio approximates to the so-called golden ratio.

The most common aspect ratio problems

  1. Everything looks narrow and elongated, faces are stretched vertically. This can happen, for example, when you watch a widescreen video (16:9 aspect ratio) on a regular TV set that has a 4:3 aspect ratio; your video is stretched vertically to fit the screen of the TV set (see Figure 2).
    16:9 video stretched to 4:3

    Figure 2: Video stretched to 4:3 compared with the original (16:9)

  2. Everything looks flattened out. This can happen if you watch an old movie or TV show that was shot in a 4:3 aspect ratio on a widescreen TV set, so that the images are stretched horizontally (see Figure 3). 4:3 video stretched to 16:9

    Figure 3: Video stretched to 16:9 compared with the original (4:3)

Solving the aspect ratio problem

Many problems connected with aspect ratio can be solved by tweaking hardware settings – configuring a DVD player or TV set to the appropriate aspect ratio.

If you want to convert video to a different format, you need to consider aspect ratio. Here you can find some tips on converting video without causing aspect ratio problems.

Don't confuse aspect ratio with frame size

You probably know that a pixel is the smallest unit of an image. In video files square pixel are the primary unit. Obviously, the width and height of a square pixel are equal to each other. In this case, the ratio between video dimensions in pixels will correspond to the aspect ratio of the video file. For example, a video file which consists of square pixels has a resolution of 640 by 480, and its aspect ratio is 4:3 (640 x 480 = 4:3).

However, DVD files often use rectangular pixels (the pixel width differs from its height). In this case, the ratio between video dimensions in pixels will differ from the aspect ratio of the video file. For example, a 4:3 DVD video may have a resolution of 720 by 480 (720 x 480 ≠ 4:3). This difference is caused by the different dimensions of rectangular pixels.

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