Editing in Timeline mode 99
Changing properties over time
A powerful feature of MoviePlus's Timeline mode is the ability to change opacity
over the clip's playback duration. This is done by using keyframes, placed under
the clip on the timeline. Each keyframe possesses its own properties, which affect
the clip from that keyframe position onwards. Tracks and groups can be affected
similarly. For more details, see Changing properties over time (p. 86).
Removing Backgrounds
There are a number of reasons you might want to "remove" a region of your video:
• To isolate a foreground subject in order to place them against a
different background, e.g. blue-screening such as used for movie
special effects and daily favourites like weather presenting.
• To cut out a hole in a video, e.g. a billboard advertising area or sports
stadium big screen, in order to place a video of your own in the cut out
region.
• To limit the extent of an effect e.g. to just mosaic someone's face to
respect their privacy but leave the remainder of the video unaffected.
• To crop your movie, e.g. leave just a rectangular or other-shaped
portion of your video and discard the remainder, perhaps leaving
room for other cropped videos on screen to sit alongside to form a
montage, popularized by comic book hero movies.
The cutting out of regular shapes and cropping of video is something you can
achieve using masks. The removal of a solid-coloured background can be
achieved using a Chroma Key effect, also called blue-screening/green-screening,
matting, colour keying and colour separation overlays.
Masking
Masks are a way of using an image to "cut out" a rectangular or other-shaped
portion from a video, leaving transparency around the subject, effectively
removing a background to give focus to a foreground element. You can also use
masks to crop video for multiple picture-in-picture effects. Masks can also
