Working with pal video, What’s an a frame – Apple Cinema Tools 4 User Manual
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Note that there is not a one-to-one correspondence between film frames and video
frames after this pull-down occurs. The duration of a video frame is four-fifths the duration
of a film frame. Because of this discrepancy, if you tried to match a specific number of
whole video frames to some number of whole film frames, the durations would seldom
match perfectly. In order to maintain overall synchronization, there is usually some fraction
of a film frame that must be either added to or subtracted from the duration of the next
edit. This means that in the cut list, Cinema Tools occasionally has to add or subtract a
film frame from the end of a cut in order to maintain synchronization. For this reason, if
you edit 3:2 pull-down video, the Cinema Tools cut list is only accurate to within +/–
1 frame on each edit.
This accuracy issue is easily resolved by using the Reverse Telecine feature (or third-party
hardware or software) to remove the extra fields and restore the film’s original 24 fps rate
before you begin editing digitally, providing a one-to-one relationship between the video
and film frames. Setting the Final Cut Pro editing timebase in the Sequence Preset Editor
to 24 fps (or 23.98 fps—see
Synchronizing the Audio with the Video
) allows you to edit
the video and generate a very accurate cut list. See
Determining How to Prepare Source
for more information about issues related to these options.
What’s an A Frame?
You will see and hear references to “A” frames whenever you are involved with 3:2
pull-down video. As the previous illustration shows, the A frame is the only one that
has all its fields contained within one video frame. The others (B, C, and D frames) all
appear in two video frames. Because the A frame is the start of the video five-frame
pattern, it is highly desirable to have one as the first frame in all video clips. It’s common
practice to have A frames at non-drop frame timecode numbers ending in “5” and “0.”
See
for more information.
Working with PAL Video
The PAL video frame rate is exactly 25 fps. There are two methods used when transferring
film to PAL: running the film at 25 fps (referred to as the 24 @ 25 method), and adding
two extra fields per second (similar to NTSC’s 3:2 pull-down, referred to as the 24 & 1
method, or the 24 @ 25 pull-down method).
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Chapter 2
Before You Begin Your Film Project