Adobe AFTER EFFECTS 5.5 Help Manual page 42

Adobe After Effects Help
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Preparing a movie for import when final output is NTSC inter-
laced video
You can edit and prepare video footage in other applications, such as Adobe Premiere,
before importing it into After Effects. If you want to render the footage from After Effects
as NTSC interlaced video, do not field-render or create interlaced frames when you render
the movie from the other application. It's acceptable to render interlaced video for
temporary files, but 60 progressive gives better quality. Make sure that you keep track of
the original field order so you can correctly render it in After Effects. See "Field rendering"
on page 44 and "Testing the field-rendering order" on page 302.
As long as the footage is on a computer, it should remain noninterlaced. Keeping the
footage in noninterlaced format preserves more image quality and saves you the extra
step of separating fields in After Effects. Once it's ready to go to your nonlinear editor, such
as Adobe Premiere, it should be interlaced.
When you render the movie from the other application, render it at 60 fps of frame-
rendered (noninterlaced) video. After you integrate it into a composition, After Effects can
render it to high-quality field-rendered (interlaced) frames at 30 fps for videotape.
Preparing motion-footage frame rates for final output
When you import motion footage into After Effects, the file's frame rate does not change. If
you plan to output your footage to a different frame rate, you can make it conform to the
new frame rate in After Effects. Conforming ensures that frames disperse evenly over the
new output frame rate.
Conforming footage does not alter the original footage, only the reference that is used by
After Effects. When it conforms, After Effects changes the internal duration of frames but
does not change the frame content. If the conformation is a large amount, the footage
plays back at a different speed. For example, if you change the frame rate from 15 fps to 30
fps, the footage plays back faster.
It's best to make the frame rate the same as the final output frame rate for your project.
This way, After Effects renders each frame, and the final output does not omit or duplicate
frames. However, in order not to drastically change the speed of your motion footage, it
may be beneficial to conform only by a small amount, making the new frame rate divisible
by the output rate. For example, if your original footage has a frame rate of 29.97 fps and
you want to output it for playback on CD-ROM at 10 fps, you can conform to 30 fps. At 30
fps, the frames are divisible by 10, so After Effects can evenly render every third frame.
Note: If you want to output original NTSC footage as PAL or vice versa, you must have
access to hardware that supports each format.
To change the frame rate of a motion footage file:
1 Select the footage file in the Project window.
2 Choose File > Interpret Footage > Main.
3 Select Conform to Frame Rate, and type a new frame rate in the Frames Per Second box.
Then click OK.
Note: This procedure can change the synchronization of audio and video files. Be sure to
check your files and make any necessary adjustments.
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