# init(format:frameCapacity:initializingWith:) Creates a read-only buffer by allocating and initializing audio data via closure. ``` init(format: AVAudioFormat, frameCapacity: Int, initializingWith: (UnsafeMutablePointer) throws -> Void) throws ``` ## Parameters `format` The audio format for the buffer. `frameCapacity` The capacity in audio frames. `initializingWith` Closure that receives the mutable AudioBufferList to initialize. ## Discussion> Throws: An error if allocation fails or the closure throws. --- 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)