Most object replacement plugins use a concept of identifying the unwanted portion of an image and then using an offset to grab a different portion of the image. This is then placed over the unwanted object and tracked throughout the moving video. To do this manually could be tedious if the video image is complex. One way would be to create a still frame of the video and either crop to a section that is a suitable replacement for where the unwanted object is, or bring that still into a photo editor and cut out the replacement section (square, circle, etc.). Then you can place that over the unwanted object and using blend modes and/or opacity adjustments tweak it to look as natural as possible. Once that is done you'll have to keyframe the position of the replacement throughout the moving video. You could also duplicate the original video clip, stack it below the clip you want to remove something from and then scale or reposition the clip so a useful part of the image is under the unwanted object. From there you can create a shape mask on the original clip and cut out the object revealing the replacement section beneath it. You will still have to keyframe the position of the mask throughout the video to track it. The Coremelt plugin Slice-X is a much better solution and much faster.
/7 oops, beat by the minute by dgwvideo… my paintings wasted time so, as an addendum //
Welcome megasap to fcp.co
… basically … double the layer, select a portion of the frames content by masking it, and transform/move it 'over' the unwanted object. Adjust portion of the plaster by key framing it.
… but … you run into several problems:
a) you need a clean-plate = the part of the frame 'behind' the object
b) you have to be able to mask the 'plaster'/clone super-precisely
c) you have to adjust the position of the clone-stamp super-precisely - this includes object's movements, camera's movements (imagine shaky freehand), zoom, motion-blur etc....
the coremelt plugins can help to adopt position in x/y instead of painstaking frame-by-frame rotoscoping, but can not do wonders either … example: no content avail to clone, camera rotates, no precise selection possible (blur) ....