# Audio File Services Read or write a variety of audio data to or from disk or a memory buffer. ## Discussion This document describes Audio File Services, a C programming interface that enables you to read or write a wide variety of audio data to or from disk or a memory buffer. With Audio File Services you can: - Create, initialize, open, and close audio files - Read and write audio files - Optimize audio files - Work with user data and global information ## Topics ### Creating and Initializing Audio Files [`AudioFileCreateWithURL`](/documentation/AudioToolbox/AudioFileCreateWithURL(_:_:_:_:_:)) Creates a new audio file, or initializes an existing file, specified by a URL. [`AudioFileInitializeWithCallbacks`](/documentation/AudioToolbox/AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:)) Deletes the content of an existing file and assigns callbacks to the audio file object. ### Opening and Closing Audio Files [`AudioFileOpenURL`](/documentation/AudioToolbox/AudioFileOpenURL(_:_:_:_:)) Open an existing audio file specified by a URL. [`AudioFileOpenWithCallbacks`](/documentation/AudioToolbox/AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)) Opens an existing file with callbacks you provide. [`AudioFileClose`](/documentation/AudioToolbox/AudioFileClose(_:)) Closes an audio file. ### Reading and Writing Audio Files [`AudioFileReadBytes`](/documentation/AudioToolbox/AudioFileReadBytes(_:_:_:_:_:)) Reads bytes of audio data from an audio file. [`AudioFileWriteBytes`](/documentation/AudioToolbox/AudioFileWriteBytes(_:_:_:_:_:)) Writes bytes of audio data to an audio file. [`AudioFileReadPacketData`](/documentation/AudioToolbox/AudioFileReadPacketData(_:_:_:_:_:_:_:)) Reads packets of audio data from an audio file. [`AudioFileWritePackets`](/documentation/AudioToolbox/AudioFileWritePackets(_:_:_:_:_:_:_:)) Writes packets of audio data to an audio data file. ### Getting and Setting Audio File Properties [`AudioFileGetProperty`](/documentation/AudioToolbox/AudioFileGetProperty(_:_:_:_:)) Gets the value of an audio file property. [`AudioFileGetPropertyInfo`](/documentation/AudioToolbox/AudioFileGetPropertyInfo(_:_:_:_:)) Gets information about an audio file property, including the size of the property value and whether the value is writable. [`AudioFileSetProperty`](/documentation/AudioToolbox/AudioFileSetProperty(_:_:_:_:)) Sets the value of an audio file property ### Working with User Data [`AudioFileCountUserData`](/documentation/AudioToolbox/AudioFileCountUserData(_:_:_:)) Gets the number of user data items with a specified ID in a file. [`AudioFileGetUserDataSize`](/documentation/AudioToolbox/AudioFileGetUserDataSize(_:_:_:_:)) Gets the size of a user data item in an audio file. [`AudioFileGetUserDataSize64`](/documentation/AudioToolbox/AudioFileGetUserDataSize64(_:_:_:_:)) Gets the size of a user data item in an audio file. [`AudioFileGetUserData`](/documentation/AudioToolbox/AudioFileGetUserData(_:_:_:_:_:)) Gets a chunk from an audio file. [`AudioFileGetUserDataAtOffset`](/documentation/AudioToolbox/AudioFileGetUserDataAtOffset(_:_:_:_:_:_:)) Gets part of the data from a chunk in an audio file. [`AudioFileSetUserData`](/documentation/AudioToolbox/AudioFileSetUserData(_:_:_:_:_:)) Sets a user data item in an audio file. [`AudioFileRemoveUserData`](/documentation/AudioToolbox/AudioFileRemoveUserData(_:_:_:)) Removes a user data item from an audio file. ### Working with Global Information [`AudioFileGetGlobalInfoSize`](/documentation/AudioToolbox/AudioFileGetGlobalInfoSize(_:_:_:_:)) Gets the size of a global audio file property. [`AudioFileGetGlobalInfo`](/documentation/AudioToolbox/AudioFileGetGlobalInfo(_:_:_:_:_:)) Copies the value of a global property into a buffer. ### Optimizing Audio Files [`AudioFileOptimize`](/documentation/AudioToolbox/AudioFileOptimize(_:)) Consolidates audio data and performs other internal optimizations of the file structure. ### Parsing Audio File Content [`NextAudioFileRegion`](/documentation/AudioToolbox/NextAudioFileRegion(_:)) Finds the next audio file region in a region list. [`NumAudioFileMarkersToNumBytes`](/documentation/AudioToolbox/NumAudioFileMarkersToNumBytes(_:)) Returns the number of bytes corresponding to a specified number of audio file markers. [`NumBytesToNumAudioFileMarkers`](/documentation/AudioToolbox/NumBytesToNumAudioFileMarkers(_:)) A macro that returns the number of audio file markers represented by a specified number of bytes. ### Callbacks [`AudioFile_ReadProc`](/documentation/AudioToolbox/AudioFile_ReadProc) Reads audio data when used in conjunction with the [`AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)) or [`AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:)) functions.) [`AudioFile_WriteProc`](/documentation/AudioToolbox/AudioFile_WriteProc) A callback for writing file data when used in conjunction with the [`AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)) or [`AudioFileCreateWithURL(_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileCreateWithURL(_:_:_:_:_:)) functions. [`AudioFile_GetSizeProc`](/documentation/AudioToolbox/AudioFile_GetSizeProc) Gets file data size. [`AudioFile_SetSizeProc`](/documentation/AudioToolbox/AudioFile_SetSizeProc) Sets file data size. ### Data Types [`AudioBytePacketTranslationFlags`](/documentation/AudioToolbox/AudioBytePacketTranslationFlags) [`AudioFileFDFTable`](/documentation/AudioToolbox/AudioFileFDFTable) [`AudioFileFDFTableExtended`](/documentation/AudioToolbox/AudioFileFDFTableExtended) [`AudioFileFlags`](/documentation/AudioToolbox/AudioFileFlags) [`AudioFileRegionFlags`](/documentation/AudioToolbox/AudioFileRegionFlags) Flags that specify a playback direction for an audio file region structure. [`AudioFileStreamParseFlags`](/documentation/AudioToolbox/AudioFileStreamParseFlags) [`AudioFileStreamPropertyFlags`](/documentation/AudioToolbox/AudioFileStreamPropertyFlags) [`AudioFileStreamSeekFlags`](/documentation/AudioToolbox/AudioFileStreamSeekFlags) [`AudioFileID`](/documentation/AudioToolbox/AudioFileID) An opaque data type that represents an audio file object. [`AudioFilePropertyID`](/documentation/AudioToolbox/AudioFilePropertyID) An audio file property identifier. [`AudioFile_SMPTE_Time`](/documentation/AudioToolbox/AudioFile_SMPTE_Time) A data structure for describing SMPTE (Society of Motion Picture and Television Engineers) time. [`AudioFileMarker`](/documentation/AudioToolbox/AudioFileMarker) Annotates a position in an audio file. [`AudioFileMarkerList`](/documentation/AudioToolbox/AudioFileMarkerList) A list of markers associated with an audio file, including their SMPTE time type, the number of markers, and the markers themselves. [`AudioFileRegion`](/documentation/AudioToolbox/AudioFileRegion) An audio file region specifies a segment of audio data. [`AudioFileRegionList`](/documentation/AudioToolbox/AudioFileRegionList) A list of the audio file regions in a file. [`AudioFramePacketTranslation`](/documentation/AudioToolbox/AudioFramePacketTranslation) A structure that specifies frame and packet translations. [`AudioBytePacketTranslation`](/documentation/AudioToolbox/AudioBytePacketTranslation) A data structure used by the [`kAudioFilePropertyByteToPacket`](/documentation/AudioToolbox/kAudioFilePropertyByteToPacket) and [`kAudioFilePropertyPacketToByte`](/documentation/AudioToolbox/kAudioFilePropertyPacketToByte) properties. [`AudioFilePacketTableInfo`](/documentation/AudioToolbox/AudioFilePacketTableInfo) Contains information about the number of valid frames in a file and where they begin and end. [`AudioFileTypeAndFormatID`](/documentation/AudioToolbox/AudioFileTypeAndFormatID) A specifier for the constant[`kAudioFileGlobalInfo_AvailableStreamDescriptionsForFormat`](/documentation/AudioToolbox/kAudioFileGlobalInfo_AvailableStreamDescriptionsForFormat). [`AudioIndependentPacketTranslation`](/documentation/AudioToolbox/AudioIndependentPacketTranslation) [`AudioPacketDependencyInfoTranslation`](/documentation/AudioToolbox/AudioPacketDependencyInfoTranslation) [`AudioPacketRangeByteCountTranslation`](/documentation/AudioToolbox/AudioPacketRangeByteCountTranslation) [`AudioPacketRollDistanceTranslation`](/documentation/AudioToolbox/AudioPacketRollDistanceTranslation) ### Enumerations [`AudioBytePacketTranslationFlags`](/documentation/AudioToolbox/AudioBytePacketTranslationFlags) [`AudioFileFlags`](/documentation/AudioToolbox/AudioFileFlags) [`AudioFilePermissions`](/documentation/AudioToolbox/AudioFilePermissions) Flags for use when opening an audio file. [`AudioFileRegionFlags`](/documentation/AudioToolbox/AudioFileRegionFlags) Flags that specify a playback direction for an audio file region structure. [`AudioFileStreamParseFlags`](/documentation/AudioToolbox/AudioFileStreamParseFlags) [`AudioFileStreamPropertyFlags`](/documentation/AudioToolbox/AudioFileStreamPropertyFlags) [`AudioFileStreamSeekFlags`](/documentation/AudioToolbox/AudioFileStreamSeekFlags) ### Constants [`AudioFileTypeID`](/documentation/AudioToolbox/AudioFileTypeID) Operating system constants that indicate the type of file to be written or a hint about what type of file to expect from data provided. [Audio File Creation Flags](/documentation/AudioToolbox/audio_file_creation_flags) Flags to set when creating an audio file. [`AudioFilePermissions`](/documentation/AudioToolbox/AudioFilePermissions) Flags for use when opening an audio file. [Audio File Loop Direction Constants](/documentation/AudioToolbox/1576494-audio-file-loop-direction-consta) The playback direction of a looped segment of an audio file. [Audio File Marker Types](/documentation/AudioToolbox/1576492-audio-file-marker-types) A type of marker within a file used in the `mType` field of the [`AudioFileMarker`](/documentation/AudioToolbox/AudioFileMarker) structure. [`AudioFileRegionFlags`](/documentation/AudioToolbox/AudioFileRegionFlags) Flags that specify a playback direction for an audio file region structure. [Audio File Packet Translation Flags](/documentation/AudioToolbox/audio_file_packet_translation_flags) Flags specified in a packet translation structure. [Info String Keys](/documentation/AudioToolbox/info-string-keys) Key values of properties to get and set using Audio File Services functions and provide a common way to get the same information out of several different kinds of files. [Audio File Properties](/documentation/AudioToolbox/1576499-audio-file-properties) Properties used by the functions described in getting and setting pieces of data in audio files. See Working with Global Information for details. [Audio File Global Info Properties](/documentation/AudioToolbox/1576495-audio-file-global-info-propertie) Access these properties using the functions described in Working with Global Information. ### Result Codes This table lists the result codes defined for Audio File Services. [`kAudioFileUnspecifiedError`](/documentation/AudioToolbox/kAudioFileUnspecifiedError) An unspecified error has occurred. [`kAudioFileUnsupportedFileTypeError`](/documentation/AudioToolbox/kAudioFileUnsupportedFileTypeError) The file type is not supported. [`kAudioFileUnsupportedDataFormatError`](/documentation/AudioToolbox/kAudioFileUnsupportedDataFormatError) The data format is not supported by this file type. [`kAudioFileUnsupportedPropertyError`](/documentation/AudioToolbox/kAudioFileUnsupportedPropertyError) The property is not supported. [`kAudioFileBadPropertySizeError`](/documentation/AudioToolbox/kAudioFileBadPropertySizeError) The size of the property data was not correct. [`kAudioFilePermissionsError`](/documentation/AudioToolbox/kAudioFilePermissionsError) The operation violated the file permissions. For example, an attempt was made to write to a file opened with the `kAudioFileReadPermission` constant. [`kAudioFileNotOptimizedError`](/documentation/AudioToolbox/kAudioFileNotOptimizedError) The chunks following the audio data chunk are preventing the extension of the audio data chunk. To write more data, you must optimize the file. [`kAudioFileInvalidChunkError`](/documentation/AudioToolbox/kAudioFileInvalidChunkError) Either the chunk does not exist in the file or it is not supported by the file. [`kAudioFileDoesNotAllow64BitDataSizeError`](/documentation/AudioToolbox/kAudioFileDoesNotAllow64BitDataSizeError) The file offset was too large for the file type. The AIFF and WAVE file format types have 32-bit file size limits. [`kAudioFileInvalidPacketOffsetError`](/documentation/AudioToolbox/kAudioFileInvalidPacketOffsetError) A packet offset was past the end of the file, or not at the end of the file when a VBR format was written, or a corrupt packet size was read when the packet table was built. [`kAudioFileInvalidFileError`](/documentation/AudioToolbox/kAudioFileInvalidFileError) The file is malformed, or otherwise not a valid instance of an audio file of its type. [`kAudioFileOperationNotSupportedError`](/documentation/AudioToolbox/kAudioFileOperationNotSupportedError) The operation cannot be performed. [`kAudioFileNotOpenError`](/documentation/AudioToolbox/kAudioFileNotOpenError) The file is closed. [`kAudioFileEndOfFileError`](/documentation/AudioToolbox/kAudioFileEndOfFileError) End of file. [`kAudioFilePositionError`](/documentation/AudioToolbox/kAudioFilePositionError) Invalid file position. [`kAudioFileFileNotFoundError`](/documentation/AudioToolbox/kAudioFileFileNotFoundError) File not found. --- 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)