An approach to user-assisted video object extraction at pixellevel framework that aims at reducing users' workload while making full use of user interaction. The framework takes over multi-pass scan on a video sequence and bidirectional tracking on the sequence's sub-shots during each pass. Systems based on this framework can not only free users from laborious work, but also be allowed to embed various complex but effective tracking algorithms. To fulfill a system, we propose an extended Intelligent Scissors for machine to precisely track VOs. The approach to tracking is a multi-level process, locating VO boundaries from a coarse level to a fine one and yielding pixelaccurate results of extraction. Experiments on MPEG test sequences show that this approach together with the proposed framework performs well in practice.