Autodesk 64006-051108-9001 User Guide - Page 108

Image Aspect Ratio MPEG-2

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100 Chapter 7: Formats Image Aspect Ratio (MPEG-2) The other method of handling aspect ratio is to define the number of pixels in the image and the aspect ratio of the final image, then stretch or compress the pixels to the needed proportions to match the output size. This is generally how MPEG-2 works. MPEG-2 is usually displayed at 4:3 (NTSC/PAL), 16:9 (HDTV) and 2.21:1 (Cinemascope) ratios. Regardless of the aspect ratio, MPEG-2 is usually stored at a resolution of 720x480 pixels (NTSC) or 720x576 (PAL). For example, you might want the viewers to be able to see both a 4:3 and 16:9 version of the movie on a DVD title you are developing. To accomplish this, you generally produce two different versions of the movie. Although each movie is normally stored at 720x480, each is displayed at a different size depending on the aspect ratio you specify. How the movie is displayed depends on the MPEG-2 player. Generally, players display the movie at the full width of your monitor and leave black letterbox bars on movies that are not 4:3. In our example, when the 4:3 version of the movie is displayed on a 640x480 resolution monitor, the image will occupy 640x480 of the monitor's square pixels since 4:3 is the same aspect ratio as both the computer screen and the movie. Depending on your player, if you display a 16:9 version on the same screen, the image will occupy 640x360 of the monitor's square pixels, and there will be black bars on the top and bottom of the screen. If you look at the source movies of the project at their full 720x480 pixel resolution, displayed with square pixels, they will look distorted. Objects in the 4:3 aspect ratio version will look too wide, and those in the 16:9 will look too narrow. However, when displayed at their correct aspect ratio, they both look normal. The one exception to the MPEG-2 use of image aspect ratio is a mode for pixel aspect ratios of 1:1. This special case is typically used for multimedia projects, where the video is intended to be displayed on a computer monitor with square pixels. See "Preventing Distortion" on page 41 for more information on working with non-square pixel video.

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Chapter 7: Formats
100
Image Aspect Ratio (MPEG-2)
The other method of handling aspect ratio is to define the number of pixels in the image and
the aspect ratio of the final image, then stretch or compress the pixels to the needed proportions
to match the output size. This is generally how MPEG-2 works.
MPEG-2 is usually displayed at 4:3 (NTSC/PAL), 16:9 (HDTV) and 2.21:1 (Cinemascope) ratios.
Regardless of the aspect ratio, MPEG-2 is usually stored at a resolution of 720x480 pixels
(NTSC) or 720x576 (PAL).
For example, you might want the viewers to be able to see both a 4:3 and 16:9 version of the
movie on a DVD title you are developing. To accomplish this, you generally produce two
different versions of the movie. Although each movie is normally stored at 720x480, each is
displayed at a different size depending on the aspect ratio you specify.
How the movie is displayed depends on the MPEG-2 player. Generally, players display the
movie at the full width of your monitor and leave black letterbox bars on movies that are not
4:3. In our example, when the 4:3 version of the movie is displayed on a 640x480 resolution
monitor, the image will occupy 640x480 of the monitor’s square pixels since 4:3 is the same
aspect ratio as both the computer screen and the movie. Depending on your player, if you
display a 16:9 version on the same screen, the image will occupy 640x360 of the monitor’s
square pixels, and there will be black bars on the top and bottom of the screen.
If you look at the source movies of the project at their full 720x480 pixel resolution, displayed
with square pixels, they will look distorted. Objects in the 4:3 aspect ratio version will look too
wide, and those in the 16:9 will look too narrow. However, when displayed at their correct
aspect ratio, they both look normal.
The one exception to the MPEG-2 use of image aspect ratio is a mode for pixel aspect ratios of
1:1. This special case is typically used for multimedia projects, where the video is intended to
be displayed on a computer monitor with square pixels.
See “Preventing Distortion” on page 41 for more information on working with non-square
pixel video.