Editing with Overlay Mode (Windows Only)
If you import enhancements that reference HTML files with Overlay mode, the Avid editing system creates two objects in a bin: an enhancement (marked by an ITV icon) and a corresponding matte key (marked by a Matte Key icon). This matte key overlays the video, thus creating a transparent "window" that lets the video show through.
  For information about Overlay mode, see Understanding ITV Modes.
When you edit this kind of enhancement, you should edit the enhancement, not the matte key. The matte key is linked to the enhancement, so that if you edit, delete, or otherwise modify the clip in the Timeline, the matte key is also modified.
When you monitor an enhancement that uses Overlay mode in the Timeline, a special track, labeled MO (Meta Overlay), is displayed for the matte key. Note that this track displays a Lock icon, which indicates that you cannot edit it directly. You need to edit the enhancement.
You can monitor only one Meta track and its corresponding Meta Overlay track at a time.
  Do not render the matte key, because any edit causes the Avid editing application to delete and re-create the Meta Overlay track, thus losing the render. If you need to render effects for real-time play, deselect the Meta Overlay track and render effects on tracks below it.
  The ExpertRender feature does not work correctly with sequences that use Meta Overlay tracks. Use the Render In/Out feature instead.
See Also
Editing Enhancements into the Timeline

Some features described in Help are available only in Avid Xpress Pro or Avid Xpress DV. For more information about Avid Free DV go to
www.avid.com.