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• 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. The bottom field is dominant
for DV source video. This setting does not pertain to the 720p video format, since 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.
• “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 checkbox 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 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, 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 applies only if you are using interlaced NTSC video.
Quality Tab
The Quality tab allows you to set the bit rate for your video so that it can be transcoded
to a suitable data size and quality.
In addition to the controls, the lower-right corner shows an estimate of how many minutes
of video would fit on a 4.7 GB DVD using the current settings. This time assumes a single
AIFF audio stream to be used with the MPEG-2 stream.
201Chapter 18 Creating MPEG-2 Output Files