Apple Compressor (4.0) - Manual (Page 92)

Chapter 5 Custom settings and output formats 92
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Aspect Ratio: 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 appears 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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Field Dominance: Choose whether the top field or the bottom field of your interlaced source
media file will be the dominant (first) field in the output MPEG-2 video file. If you choose
Automatic (the default), Compressor analyzes the source video and attempts to determine
field dominance automatically. The bottom field is dominant for DV source video. This setting
does not pertain to the 720p video format, because that format must be progressive.
Note: For interlaced video, the top field is also known as the upper or odd field, and the
bottom field is also known as the lower or even field.
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Choose start timecode: If you leave the checkbox unselected (the default), Compressor embeds
the source media file’s existing timecode in the output media file. Selecting this checkbox
allows you to override the source media file’s timecode and enter a new timecode value in the
timecode field. This field is dimmed unless the checkbox is selected, and if it’s left blank, the
output media file uses the default starting timecode value of 00:00:00:00.
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Drop Frame: If you select the “Choose start timecode” checkbox, and you want your timecode
to be drop frame (rather than non-drop frame), you must also select this checkbox.
Timecode is a numbering system for labeling the frames in a video sequence. The type of
timecode designed for 30 fps video has a frame counter that counts from 0 to 29 and then
increments the seconds counter and returns to 0. This type of timecode, also known as non-
drop frame timecode, maintains an accurate measure of elapsed time for true 30 fps video.
However, the NTSC frame rate is 29.97 fps, so drop frame timecode was defined to provide
a more accurate measure of elapsed time for NTSC. Drop frame timecode skips frame
numbers 0 and 1 once a minute on the minute, except for every 10 minutes. For example,
drop frame timecode 01:08:59;29 is followed by 01:09:00;02, skipping timecode numbers
01:09:00;00 and 01:09:00;01.
Note: Drop frame timecode applies only if you’re using interlaced NTSC video.