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Interpreting field order


    Interlaced video has a field order defining the order in which the two video fields (upper and lower) are displayed. A system that draws the upper lines before the lower lines is called upper-field first; one that draws the lower lines before the upper lines is called lower-field first. The order in which the fields are displayed is important, especially when the fields contain motion. If you separate video fields using the wrong field order, motion will not appear smooth.

    Some programs, including After Effects and current versions of Media 100, label the field order when rendering interlaced video files. When you import a labeled video file, After Effects honors the field order label automatically. You can override the field order using the Interpretation Rules file. For more information about field order, see Specifying interpretation rules.

    If a file does not contain a field order label, you can match the original field order of your footage. If you are not sure which field order was used to interlace a footage item, use the procedure below to find out.

To determine the original field order:

  1. Select the item in the Project window.
  2. Choose File > Interpret Footage > Main.
  3. In the Interpret Footage dialog box, select Upper Field First from the Separate Fields pop-up menu, and then click OK.
  4. In the Project window, press Alt (Windows) or Option (Mac OS) as you double-click the footage to open it in a Footage window.
  5. If the Time Controls palette is not visible, choose Window > Show Time Controls.
  6. In the Footage window, find a segment that contains one or more moving areas.
  7. Using the Frame Advance button (the Frame Advance button) on the Time Controls palette, step forward at least five frames in the Footage window. Moving areas should move consistently in one direction. If the moving areas move backward every other frame, the wrong field-separation option has been applied to the footage.
  8. Note: Analog capture cards can vary. DV or footage captures from IEEE 1394 FireWire/i.Link are always lower field first.