# CVDisplayLinkOutputCallback A type for a display link callback function that the system invokes when it’s time for the app to output a video frame. ``` typealias CVDisplayLinkOutputCallback = (CVDisplayLink, UnsafePointer, UnsafePointer, CVOptionFlags, UnsafeMutablePointer, UnsafeMutableRawPointer?) -> CVReturn ``` ## Parameters `displayLink` A display link that requests a frame. `inNow` A pointer to the current time. `inOutputTime` A pointer to the display time for a frame. `flagsIn` Currently unused. Pass 0. `flagsOut` Currently unused. Pass 0. `displayLinkContext` A pointer to app-defined data. ## Discussion Your app must register a callback function for the system to invoke with the data necessary to process and output a frame of video. Your callback must retrieve the frame with the timestamp that the `inOutputTime` parameter specifies, manipulate it if you require (for example, apply color correction or map onto a surface), and output it to the display. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)