# withAudioBufferList(blockBufferMemoryAllocator:flags:body:) Calls a closure with an audio buffer list that contains the data from a sample buffer and a block buffer backing the audio buffers. ``` func withAudioBufferList(blockBufferMemoryAllocator: CFAllocator? = kCFAllocatorDefault, flags: CMSampleBuffer.Flags = [], body: (UnsafeMutableAudioBufferListPointer, CMBlockBuffer) throws -> R) throws -> R ``` ## Parameters `blockBufferMemoryAllocator` An allocator to use for the memory block held by a [CMBlockBuffer](/documentation/CoreMedia/cmblockbuffer-api). `flags` Optional flags that control the operation. `body` A closure the system calls that contains a pointer to an and the block buffer that backs its audio buffers. ## Discussion The system may not copy the data, depending on its contiguity and 16-byte alignment. It guarantees the buffers it places in the AudioBufferList are contiguous. The system returns 16-byte-aligned buffers if you pass the [`audioBufferListAssure16ByteAlignment`](/documentation/CoreMedia/CMSampleBuffer/Flags/audioBufferListAssure16ByteAlignment) flag. --- 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)