Zooming in on pictures

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I've got several images (separate) set up in the timeline thing, with the effect "zoom" on them. It looks great on the preview video-it zooms into the pictures at a constant speed. However, when I saved and played the movie, each picture remained still for a while before zooming in. This completely ruins the timing of the video, and makes it look stupid. I've tried selecting and deselecting "Zoom smoothly", it doesn't seem to make any affect on the output movie whatsoever. I'd be extremely grateful for any help.