What is CAF? Apple Core Audio Format Explained
Apple's extensible, 64-bit container for high-resolution and very long audio recordings.
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What is CAF?
The Core Audio Format (CAF) is an audio container format developed by Apple and introduced with Mac OS X 10.4 (Tiger) in 2005. It is designed as a flexible, future-proof container for storing and transporting digital audio, overcoming size and capability limits of older formats such as WAV and AIFF.
A CAF file is built from a small file header followed by a sequence of self-describing chunks, including an audio description chunk and the audio data chunk, plus optional chunks for markers, channel layout, metadata, and more. Because CAF uses 64-bit file offsets, a single file can hold an enormous amount of audio, and it can wrap many different codecs such as Linear PCM, Apple Lossless (ALAC), AAC, and others.
How CAF Works
A CAF file consists of a small file header followed by a sequence of self-describing chunks, including a mandatory audio description chunk and an audio data chunk, plus optional chunks for markers, channel layout, and metadata.[1] Each chunk carries its own size, so new chunk types can be added without breaking existing readers.[2]
History and Standardization
Apple introduced the Core Audio Format with Mac OS X 10.4 (Tiger) in 2005 as a flexible, future-proof container, and it is documented in Apple's published CAF specification.[2] The format is also catalogued by preservation bodies such as the Library of Congress.[3]
CAF vs WAV and AIFF
Older formats like WAV and AIFF use 32-bit size fields that cap files near four gigabytes; CAF instead uses 64-bit file offsets, allowing a single file to hold an enormous amount of audio.[1] It can also wrap many codecs, including Linear PCM, Apple Lossless (ALAC), and AAC, making it more capable than those earlier containers.[2]
MKV Technical Specifications
CAF vs Other Audio Formats
| Feature | CAF | WAV | AIFF |
|---|---|---|---|
| Type | Container[1] | Container | Container |
| Compression | Codec-dependent[2] | Usually uncompressed | Uncompressed |
| File size limit | No 4 GB limit[1] | 4 GB (32-bit) | ~4 GB |
| Developer | Apple[3] | Microsoft / IBM | Apple |
| Device support | Apple-centric | Wide | Wide |
| Best for | Large macOS audio | Editing/archiving | Mac archiving |
CAF removes the 4 GB size ceiling of WAV and AIFF but is mainly used within Apple platforms.
Advantages & Disadvantages
Advantages
64-bit file offsets remove the ~4 GB ceiling of WAV and AIFF, allowing extremely long high-resolution recordings in one file.
As a container, CAF can hold Linear PCM, Apple Lossless, AAC, and other encodings rather than being tied to one codec.
Self-describing chunks for markers, channel layout, and metadata let the format grow without breaking existing parsers.
CAF is fully supported across macOS and iOS via Core Audio and is used by Apple's own pro audio applications.
Disadvantages
CAF is primarily an Apple format, so support on Windows and other systems often requires specific tools or conversion.
For simple interchange, WAV and AIFF remain more broadly recognized than CAF outside the Apple ecosystem.
Its flexible chunk structure and many codec options make CAF more complex to implement than a basic PCM file.
Common Use Cases
CAF is used where large, high-quality, or Apple-native audio storage matters.
Apple pro audio apps | FileFormer
Logic Pro, GarageBand, and Soundtrack Pro use CAF for loops, sound libraries, and high-resolution project audio.
iOS system and message audio | FileFormer
CAF is used for audio assets and recorded voice messages on iOS and macOS, including iMessage audio clips.
Long-form recording | FileFormer
Its 64-bit design suits very long single-file recordings such as lectures, performances, and field recordings.
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Try Audio Converter FreeFrequently Asked Questions
What does CAF stand for?
CAF stands for Core Audio Format, Apple's container format for storing and transporting digital audio across macOS and iOS.
How is CAF better than WAV?
CAF uses 64-bit offsets instead of WAV's 32-bit fields, so it has no practical file-size limit and can also wrap many different codecs and metadata chunks.
What codecs can a CAF file contain?
CAF can hold Linear PCM, Apple Lossless (ALAC), AAC, and a range of other codecs, since it is a container rather than a single codec.
Can CAF files be played outside Apple devices?
Yes, with the right software. Tools like FFmpeg and VLC can read many CAF files, though native support is strongest on macOS and iOS.
Is CAF lossless?
It can be. CAF itself is a container; whether the audio is lossless depends on the codec used inside, such as Linear PCM or Apple Lossless for lossless storage.