Here, we will look at how to prepare a video with a green (or blue) screen so we can later insert whatever background we want. This tutorial is primarily for iMovie though other video editing programs support green screens as well.
You will need a surface of either the same shade of blue or the same shade of green. If there are some exceptions don't worry too much, but it will impact on the quality of the final video.
Consider if there is a blue or green wall in your house, if you have a blue or green bed sheet (highly recommended - very versatile as you can cover objects and the floor) or similar. Make sure you wear clothes contrasting that colour if you are recording yourself - or iMovie will cut out body parts! If that is what you are trying to achieve (e.g. your head on a bird), go for it.
Depending on what you are trying to achieve, record the video so the whole object is over the blue or green area.
Shrink the Object
Depending on what you are trying to achieve, you may want to shrink the object you are inserting. If not, you can insert this video and can skip the rest of this post. If you want to shrink the object, read on.
iMovie does not appear to allow you to shrink the video 'on-the-fly' when inserting into another video. Therefore, we will use a workaround.
Open iMovie and click on Create New Project.
Import the video you want to insert. Drag and drop will work.
Drag the video to the timeline or click on the video then click the Plus button.
Adjust the view to the level of detail you want (I wonder if it's called 'time zoom'?).
Go to the part of the video with no object and export just that frame.
Delete the clip by pressing the 'delete' key (we will replace it as an overlay).
Import that frame into your project.
Add the clip again.
Move the clip to above the frame we added by dragging.
Trim the video to just the section you want. This can be reversed simply by re-adjusting.
Adjust the frame to the whole duration of the clip.
Crop the frame to just the blue (or green) part.
Shrink the clip. Consider the size and position you want it to be in relation to the video you are inserting into.
You can enlarge the clip when inserting into the final video and move it a bit but you cannot shrink it in iMovie using this method.
Export the final clip.
Go back to Projects, naming the project when prompted.
