Frame aspect ratio

Frame aspect ratio describes the ratio of width to height in the dimensions of an image. For example, DV NTSC has a frame aspect ratio of 4:3 (or 4.0 width by 3.0 height) and a typical widescreen frame has a frame aspect ratio of 16:9. Many cameras that have a widescreen mode can record using the 16:9 aspect ratio. Many films have been shot using even wider aspect ratios.

A 4:3 frame aspect ratio (left), and wider 16:9 frame aspect ratio (right)

When you import clips shot in one frame aspect ratio into a project that uses another frame aspect ratio, you must decide how to reconcile the different values. For example, there are two common techniques for showing a widescreen movie with a 16:9 frame aspect ratio on a standard television with a 4:3 frame aspect ratio. You can fit the entire width of the 16:9 frame in a black 4:3 frame (called letterboxing), which results in black bands above and below the widescreen frame. Or you can fill the 4:3 frame vertically with the entire height of the 16:9 frame, varying the horizontal position of the 16:9 frame behind the narrower 4:3 frame so that important action is visible in the 4:3 frame (called pan & scan). In Adobe Premiere Pro, you can implement either technique by using Motion effect properties such as Position and Scale.

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NTSC displays

A.

16:9 NTSC footage

B.

DVD player display using original widescreen format on widescreen TV screen

C.

16:9 image on a 4:3 TV screen cropped using automatic pan and scan

D.

16:9 image on a 4:3 TV screen using automatic letterboxing to reduce overall frame size and display entire image

Pixel aspect ratio

Pixel aspect ratio describes the ratio of width to height of a single pixel in a frame. Pixel aspect ratios vary because different video systems make various assumptions about the number of pixels required to fill a frame. For example, many computer video standards define a 4:3 aspect ratio frame as 640 pixels wide by 480 pixels high, which results in square pixels. Video standards such as DV NTSC define a 4:3 aspect ratio frame as 720x480 pixels, which results in narrower, rectangular pixels because there are more pixels within the same frame width. The computer video pixels in this example have a pixel aspect ratio of 1:1 (square), whereas the DV NTSC pixels have a pixel aspect ratio of 0.9 (nonsquare). DV pixels, which are always rectangular, are vertically oriented in systems producing NTSC video and horizontally oriented in systems producing PAL video. Adobe Premiere Pro displays a clip’s pixel aspect ratio next to the clip’s image thumbnail in the Project panel.

If you display rectangular pixels on a square‑pixel monitor without alteration, images appear distorted; for example, circles distort into ovals. However, when displayed on a broadcast monitor, the images appear correctly proportioned because broadcast monitors use rectangular pixels. Adobe Premiere Pro can display and output clips of various pixel aspect ratios without distortion because it attempts to automatically reconcile them with the pixel aspect ratio of your project.

You may occasionally encounter a distorted clip if Adobe Premiere Pro interprets pixel aspect ratio incorrectly. You can correct the distortion of an individual clip by manually specifying the source clip’s pixel aspect ratio in the Interpret Footage dialog box. You can correct similar misinterpretations of groups of same-size files by editing the file Interpretation Rules.txt.

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Pixel and frame aspect ratios

A.

4:3 square‑pixel image displayed on 4:3 square‑pixel (computer) monitor

B.

4:3 square‑pixel image interpreted correctly for display on 4:3 non‑square pixel (TV) monitor

C.

4:3 square‑pixel image interpreted incorrectly for display on 4:3 non‑square pixel (TV) monitor