Which of the following best describes an overlay in video production?

An overlay in video production primarily refers to a visual effect or graphic that is placed on top of the primary image or video content. This can include elements such as text graphics, logos, or any other visual imagery that enhances the primary content without altering it. Overlays are commonly used to provide additional information, visual flair, or branding within a broadcast or video segment.

In contrast to other options, a background music track serves as audio enhancement and doesn't incorporate visual elements, making it unrelated to the concept of an overlay. A camera angle switch refers to changing the perspective from which a scene is viewed, which is a function of cinematography rather than a visual component layered over existing content. Meanwhile, transitions between scenes involve moving from one scene to another, typically through techniques like fades or cuts, which also do not fit the definition of an overlay. Therefore, the strongest alignment with the concept of an overlay in video production is indeed the visual effect on a video.