Apple Compressor 2 User Manual
Page 132
132
Chapter 10
Creating MPEG-2 Output Files
 Rate: Choose the intended frame rate for the MPEG-2 output file. Film and some new
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 “
page 133 for more information.
 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.
 Field Dominance pop-up menu: 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. Bottom field
is dominant for DV source video. This setting pertains only to interlaced video output
formats, not 720p.
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.
 “Choose start timecode” checkbox and field: If you leave the checkbox deselected (the
default), Compressor embeds the source media file’s existing timecode into the
output media file. Selecting this box allows you to override the source media file’s
existing timecode and enter a new timecode in the timecode field. This field remains
dimmed unless the checkbox is selected, and if it is left blank, the output media file
uses the default timecode of 00:00:00:00.
 “Drop frame” checkbox: If you have already selected 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 which 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, and 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 timecodes 01:09:00;00 and 01:09:00;01.
Note: Drop frame timecode only applies if you are using interlaced NTSC video.