B-roll: cover the frame where the words ask for a picture

B-roll, also called cutaway footage, is the extra material shown over your main video: a product shot, a screen, a document, a detail of the thing being discussed. The main shot — the one where someone is talking to camera — is A-roll. B-roll does not replace it; the audio keeps running while the picture illustrates what is being said.

B-roll shows the subject of the sentence instead of describing it. Cutaways help hold attention through a long stretch of one person talking, and they let you cover an edit that would otherwise read as a jump.

Here b-roll is a manual track inside the subtitle editor: you bring your own clip or still, set the interval it covers, add a zoom if the shot needs one, and render just that stretch to check it.

A zoom is a scale and a centre point over an interval. Push in slightly on a reaction, hold, and let it out — the frame changes without a cut, and the viewer reads it as emphasis rather than as editing.

On a static talking head this is the cheapest rhythm available. You have no second camera, but you do have pixels to spare: a shot framed with headroom survives a fifteen percent push with nothing to spare visually.

Zooms and b-roll solve the same problem from opposite ends. A zoom keeps the speaker and changes the framing; an overlay drops the speaker and shows the thing. Alternating them is what keeps a long stretch of one person talking watchable.

Both are stored as plain intervals on the edit, so nothing is baked until you export. Move a zoom, shorten an overlay, render the segment again — the source video is never touched.