Apple Compressor 3 User Manual
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Note: Since MPEG-2 uses fixed video frame sizes (see
), Compressor enters the output frame size in the fields in the Geometry pane
based on your video format selection.
The video format you choose determines the options for the associated characteristics
such as frame size and rate, aspect ratio, and field dominance.
Note: The normal frame dimensions of standard definition (SD) NTSC digital video are
720 x 486. If you want to transcode a source file using the NTSC setting, Compressor
crops the file to achieve the required MPEG-2 frame size of 720 x 480, unless you have
already specified cropping attributes for your setting. If not, Compressor crops two
rows of pixels from the top and four from the bottom. This crop attribute is only
temporary and is not saved in the setting. You can see the effects of the crop by
double-clicking the setting in the job to open the Preview window.
• Frame Rate pop-up menu: Choose the intended frame rate for the MPEG-2 output file.
Film and some video camcorders create progressive material at 24 fps (or the NTSC
variant 23.98 fps). Although the term “24p” implies video with a frame rate of 24 fps,
the frame rate is usually 23.976 fps (rounded to 23.98) fps. To transcode these sources
for DVD playback on NTSC-related TVs, choose the 23.98 setting. See
for more information.
Note: The NTSC frame rate is frequently mentioned as 29.97 fps. Similarly, the “NTSC
version” of 24 fps is mentioned as 23.98 fps. Both these numbers are actually
approximations to the true values 30/1.001 and 24/1.001, or 29.97003 and 23.97602
shown to more decimal places. These numbers show that 29.97 is a pretty good
approximation to 30/1.001 (only 3 frames drift in 100,000 seconds), but that 23.976
would be much better than 23.98. In fact, even though 23.98 is used as shorthand in
the Compressor Help and in the Compressor user interface, accuracy of 23.976 or better
is maintained internally in Compressor, and generally within QuickTime as well. See
for more information on this topic.
• Aspect Ratio pop-up menu: Choose the aspect ratio of your video file. The default is 4:3.
The other option of 16:9 is used for anamorphic DVD. The aspect ratio determines how
the picture fills the television screen. A 16:9 (widescreen) DVD viewed on a typical 4:3
television displays in letterbox format (black bars at the top and bottom of the screen).
However, a widescreen DVD displayed on a 16:9 (widescreen) TV fills the screen.
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Chapter 18
Creating MPEG-2 Output Files