Darken the edges of the frame slightly to gather the eye toward the center and add a cinematic mood.
Character close-ups, emotional or flashback scenes, product cuts, and vintage looks.
If you ask for it in the prompt, the strength can vary from cut to cut, so generate plainly and apply the same strength to every cut in editing. In ffmpeg, use vignette=PI/5; the larger the value, the stronger it gets (up to PI/2). In DaVinci Resolve, blur a wide circular window and lower the brightness outside it. CapCut has a Vignette in its adjustment menu. If the border looks like a circle, it's too strong. In 9:16, use it lightly so the captions at the top and bottom don't land on the dark edges.
Darken the frame edges softly to pull attention to the center: ffmpeg -i in.mp4 -vf vignette=angle=PI/4 -c:a copy out.mp4. A smaller angle such as PI/6 makes it stronger, and avoid it on shots with text or logos in the corners.
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The David Shutt — How to create a vignette in Davinci Resolve 18 - Fast Tutorial
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