How to mask and animate a shape over video

Masks in Video by Zaweba are drawn straight onto the preview, and every one of their settings can be keyframed. One click makes a rectangle, ellipse or star, or you can draw a polygon, a pen curve or a freehand shape. Then add keys to the mask's move, scale, turn, feather and opacity so it travels, grows or fades over time.

A mask decides which part of a clip shows. Use it to reveal a picture through a shape, hide part of the frame, spotlight a detail, or limit an effect to one area such as a face that needs blurring.

Drawing the mask

Select a picture clip on the timeline. In the masks section of the Inspector, click to add a rectangle, ellipse or star, or choose a drawing tool. With the pen, click to place points and drag to pull out Bezier handles for curves. Freehand follows the mouse.

Edit the shape on the preview. Drag points and handles to reshape it. Ctrl+click the outline to add a point, and Alt+click a point to delete it. Rectangle masks can have rounded corners.

Each mask has a mode: add, subtract, intersect or difference. Several masks on one clip combine through these modes, so a ring is an ellipse with a smaller ellipse subtracted from it. Any mask can also be inverted to show everything except the shape.

Animating it

Masks animate through ordinary keyframes. Move the playhead to where the motion starts and click the diamond beside move, scale or turn to add a key. Move the playhead on, change the value, and another key is added. The mask now travels between them.

Feather and opacity animate the same way. Feathering softens the edge, so a mask that starts sharp and ends soft looks like it is dissolving. Expansion grows or shrinks the outline without changing its shape.

Choose an ease for each key: smooth, linear, ease in, ease out or hold. Bezier keys have handles for finer control, and View > Keyframe graph shows the motion as curves you can drag.

Following something that moves

Keyframing by hand works for simple paths. For a mask that should stick to a moving face or object, use mask tracking instead: Track forward or Track back on the mask follows the picture inside it and keys the position on every frame. A later mode follows two detailed spots to key rotation and scale as well, and Follow in perspective tracks four corners.

Shapes from vector files

For logos and complex outlines, import an SVG as a mask. Paths, rectangles, circles, ellipses, lines, polylines, polygons, groups with transforms and arcs are read. Any text in the SVG must be converted to outlines first. The imported mask behaves like one you drew, so it can be keyed and animated too.

Using masks well

Give an effect a mask. An effect can be set to work only inside a mask, which is how you blur a face, sharpen one area or grade a single object without touching the rest.

Feather almost always. A small feather makes most masks look natural.

Use track mattes for video inside text. When you want footage to show inside a title or a logo, a track matte, which shows a clip only inside the picture on another track, is often simpler than drawing a mask.

Colour masks select by colour rather than shape. They pick a hue, saturation and brightness range, which is handy for isolating a sky or a piece of clothing.

Video by Zaweba is free software that runs offline on Windows with no account, so masking and animation happen entirely on your own PC.