# CMAudioFormatDescriptionGetChannelLayout(_:sizeOut:) Returns a read-only pointer to, and the size of, the audio channel layout inside an audio format description. ``` func CMAudioFormatDescriptionGetChannelLayout(_ desc: CMAudioFormatDescription, sizeOut: UnsafeMutablePointer?) -> UnsafePointer? ``` ## Parameters `desc` `CMFormatDescription` being interrogated. `sizeOut` Pointer to variable that will be written with the size of the layout. Can be `NULL`. ## Return Value A read-only pointer to the `AudioChannelLayout` inside the audio format description. ## Discussion AudioChannelLayouts are optional; this API returns `NULL` if one doesn’t exist. This API is specific to audio format descriptions, and returns `NULL` if called with a non-audio format description. --- 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)