As outlined in a WWDC 2023 video, iOS 17 includes a new Cinematic API that enables developers to support Cinematic mode video playback and editing in third-party apps.

"The Cinematic framework enables you to add professional-level editing and playback features to movies, recorded with the Camera app's Cinematic mode, to your apps," says Apple's developer documentation. "These are the same features used in applications such as Final Cut Pro, Photos, and iMovie. For example, this enables your apps to change focus distance and aperture in movies, creating a bokeh effect, even after recording."

Apple offers Cinematic mode in the Camera app on iPhone 13 models and newer. Inspired by professional Hollywood films, the feature allows users to record video with a shallow depth of field and automatic focus changes between subjects.

Cinematic mode uses a technique called "rack focus" to seamlessly shift the focus from one subject to another. It does this by locking the focus on the subject in a scene and blurring the background to achieve depth of field. If you subsequently move the camera to center on a new subject, or a new subject enters the scene, Cinematic mode automatically switches the focal point to this new subject and blurs out the background.

Source: Macrumors