# CMMetadataCreateKeyFromIdentifier(allocator:identifier:keyOut:) Creates a copy of the key by using an identifier. ``` func CMMetadataCreateKeyFromIdentifier(allocator: CFAllocator?, identifier: CFString, keyOut: UnsafeMutablePointer) -> OSStatus ``` ## Parameters `allocator` The allocator to use for creating the identifier. `identifier` The identifier to be inspected. `keyOut` Upon return, a pointer to the key data that was used to create the identifier. ## Return Value If successful, a nonzero result code. See [Metadata Identifier Error Codes](/documentation/CoreMedia/metadata-identifier-errors). ## Discussion The returned `CFType` is based on the keyspace encoded in the identifier. For `OSType` keyspaces, the key will be returned as a `CFNumber`, where a big endian interpretation of its value represents the four bytes of the key’s numeric value. For the keyspaces [`kCMMetadataKeySpace_QuickTimeMetadata`](/documentation/CoreMedia/kCMMetadataKeySpace_QuickTimeMetadata) and [`kCMMetadataKeySpace_Icy`](/documentation/CoreMedia/kCMMetadataKeySpace_Icy), the key will be returned as a `CFString`. All other keyspaces will have the function return the key as a `CFData`. --- 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)