Mask transition
Also known as: matte transition, wipe-through
A transition where one shot is revealed through a shape or an object in the frame, hiding the cut behind something already in the picture.
Updated
What it means
A mask transition uses geometry instead of a dissolve. A rider passes close to the lens, a tree trunk fills the frame, and the next shot appears from behind it. Nothing announces a cut.
The frame does the work. Anything that briefly covers the picture, a wall, a hand, a wave, becomes the boundary between two clips. The darker and faster the cover, the better.
It differs from a Cross dissolve in intent. A dissolve says time passed; a mask says the camera travelled, and the second reads as deliberate camera work rather than an effect reached for in a menu.
How it works in practice
The shots have to be filmed for it. Both clips need something passing close to the lens, which means planning the pass rather than hoping for one in review. The transition is decided on location.
Movement direction has to match. A wipe travelling left needs the next shot moving left, and a mismatch reads as an error rather than as a transition, which is the same logic as Screen direction.
A Whip pan transition is the simpler relative. Both hide a cut in motion blur, and the whip needs no object in the frame to work with.
What to watch out for
It is easy to overuse. Two in a sequence read as style; five read as a template, and a viewer starts watching the transitions rather than the riding. The device stops being invisible.
Clean masking needs a clean edge. A blurred foreground object works; a detailed one requires real rotoscoping, which is work nobody does on a session edit. Filming it properly is the shortcut.
Automatic assembly joins shots with a plain Cut rather than a wipe, so a mask transition is something added afterwards on one specific pair of clips where the foreground happens to agree.
How RawClip handles it
Assembled sequences use straight cuts and a small set of plain transitions, because those hold up across any footage. A mask transition depends on two specific clips lining up, which is a manual decision made on a timeline afterwards.