I'm doing chroma key work with the intent of making an object disappear in a background of solid color and in experimenting, I've been mostly successful except for a minor glitch that renders the whole effect useless. On my "video" track I've placed a short AVI clip of a windmill situated in front of a solid, pure green background. Later, I want to use this clip to "green screen" the windmill onto another background but first, I want to make the top half of the windmill disappear and so on the "video overlay" track I placed a bitmap image of a pure green box centered on a pure blue background. The box is situated in the frame so that when the chroma keyer effect is later added to this clip, the top half of the windmill disappears in the resulting video. The problem is that one or more of the edges of the "masking" box show up in the resulting video (as darkened lines). Oddly, the edges don't always appear. You can manually reposition the box using the event pan/crop keyframe editor and get the edges to disappear but invariably, when you go to render, the edges will re-appear. Likewise, you can set the "Low Threshold" to 1.0 in the chroma keyer editor to make the edges go away but it isn't a guarantee of anything--again, the edges re-appear in the final video. What am I doing wrong? Thanks so much!