# The 3-2 Pulldown tool

The 3-2 Pulldown tool removes composite frames from a QuickTime movie. This increases the movie's perceived resolution, while reducing the bandwidth required to display it on the 3DO Interactive Multiplayer.

Only movies that start as film and are converted to analog video need 3-2 Pulldown processing. If you're not sure whether a movie was originally captured on video, follow the steps in "Identifying Composite Frames" later in this chapter to check for the composite frames present in movies converted from film to video.

## Understanding Telecine

Composite frames are intermediate frames inserted into a movie during Telecine conversion from film to video. This process converts film that displays at 24 frames per second into video tape that displays at 30 frames per second. Each set of four film frames is converted into interlaced video fields and then the video fields are reconstructed into five video frames as shown in the figure below.

The third and fourth video frames in this figure are composite frames that replace the second film frame. With these two composite frames included, the movie can be displayed at the 30 fps rate required by most analog video standards.

When analog video is converted into a QuickTime movie, however, these composite frames are included. Since the human eye often does not distinguish the difference between 24 fps and 30, you can remove the composite frames from your movie and display it at 24 fps in your 3DO application. This results in a clearer picture since the composite frames are not true digitized versions of corresponding film frames.

Figure 1: The Telecine process inserts frames.

## Choosing a movie

Currently, 3-2 Pulldown processes only QuickTime movies that meet the following criteria:

- 30 frames per second
- raw format (no compression)

You can check the frame rate of a movie and find out whether it's been compressed with a number of QuickTime tools. Apples's MovieAnalyzer tool includes the frame rate and compression codec in the information window it displays for each video track in a movie.

Note: 3-2 Pulldown requires raw source data. Make sure your movie has not been compressed with JPEG before you process it with 3-2 Pulldown.

## Field dominance

To process a QuickTime movie correctly, you need to determine its field dominance. The field dominance setting determines whether a video capture system (video tape deck, laser disk recorder, etc.) selects an even or odd interlace field as the first field it uses when creating the first frame of a movie. Below are the field dominance selections for two standard video capture systems:

    -----------------------------------------------------
    System               |Field Dominance
    -----------------------------------------------------
    Pioneer LaserRecorder|Even
    -----------------------------------------------------
    Sony Betacam         |Odd
    -----------------------------------------------------

Choose Preferences in the File menu to display the 3-2 Pulldown preferences dialog. Select either Even or Odd, depending on the field dominance of your movie. If you do not know what system was used to capture it, choose Odd (the most common field dominance) and then check for a field dominance error when saving the processed movie. See "Incorrect Field Dominance" under "Troubleshooting" to learn how to check for field dominance errors.

## Removing composite frames

To process a movie:

- mark the composite frames
- check the frame markers
- save the movie

When you open 3-2 Pulldown, the standard File dialog appears. Select the movie you want to process and click Open. The movie displays in a standard movie player window. You can step forward or backward by clicking on the frame-advance icons in the lower-right corner of the display or by using the left and right arrow keys.

### Identifying composite frames

As you step through the movie, two out of every five frames should be composites. Since the composite frames are created from interlace fields from two different film frames, you can identify them by the misalignment or "aliasing" of the interlace fields. Below is an example of a sequence of frames.

Figure 2: Composite frames show misaligned fields.

When you identify a pair of composite frames, mark the first one by choosing Mark from the Frame menu. Doing this identifies the composite frame as the first in a pair that will be converted into a reconstructed frame by 3-2 Pulldown.

A status bar under the movie window shows the time, frame, and phase numbers for the frame displayed. 3-2 Pulldown updates the status bar as you step through the movie. The green rectangle in the status bar represents a mark for that frame.

The phase counter represents the five-frame sequence of true and composited frames that 3-2 Pulldown expects. If the sequence of composite frames goes out of phase, return to the last correctly marked set of composite frames and review the movie again until you can identify and mark the next set of composite frames.

### Identifying composite frame sequences in edited film

With film that has been edited after Telecine processing, there can be three composite frames in sequence. This usually occurs when two sets of composite frames are combined during editing of a video tape. Of the three composite frames, two should form one reconstructed frame and one remains as an "orphan" frame.

Figure 3: Correctly and incorrectly marked composite frames.

The figure above shows the results of marking two different frames. In this sequence frames 1 and 2 are the correct set of composite frames. Marking frame 1 results in a true reconstructed frame. Marking frame 2 results in a reconstructed frame that remains aliased.

### Marking a movie

It may take several passes through a movie to mark all the composite frames correctly. Because edits may change the sequence of composite frames, you cannot assume that marking the first set of composite frames synchronizes the reconstruction process for the remainder of the movie. To speed up the review process, use the tab key to step through the marked frames.

## Saving a processed movie

Choose Save as Pulldown from the File menu to save the movie. When 3-2 Pulldown saves, it displays the reconstructed frames as they are created. Check each reconstructed frame for the interlace field aliasing that indicates an incorrectly reconstructed frame. You may need to reset the frame markers and save the movie again.

Uncompressed QuickTime movies take up large amounts of disk space. Processing to remove composited frames requires enough disk space to store both the unprocessed and processed versions of the movie. Removing composited frames-that is, one out of every five-reduces the size of the unprocessed movie by approximately 20 percent and cuts the required disk space accordingly.

It is possible that a processed movie will contain fewer composited frames if it's edited after Telecine processing, resulting in a final file size greater than 80 percent of the number of pre-Telecine frames. The processed movie will never be larger than the unprocessed movie, however.

## Troubleshooting

Some common problems that arise with video processing and their solutions are listed below.

### Synchronizing audio

A processed movie should contain 80 percent of the number of frames as the unprocessed movie. For example, a 900-frame movie should contain 720 frames after 3-2 Pulldown processing. If an unprocessed film contains more than the normal number of composite frames as a result of post-Telecine editing, the processed film may not contain the expected number of total frames. This can put the movie's audio track out of sync with the video track, and you may have to paste frames back into the video track to restore video and audio synchronization.

### Incorrect field dominance

If you've chosen the wrong field dominance, the reconstructed frames created by 3-2 Pulldown will not be correctly interlaced. Instead of the interlace fields matching correctly, they will be aliased to a greater degree than they were in the corresponding composite frames. To remedy this, change the field dominance in the Preferences dialog and save the movie again.