CAF (Core Audio Format)
Apple's container that handles audio files of any size, any codec, and any sample rate without the old WAV or AIFF limits.
| Full name | Core Audio Format |
| Extension | .caf |
| MIME type | audio/x-caf |
| Developer | Apple Inc. |
| Released | 2005 (specification published March 2006) |
| Type | Audio container format |
| Max file size | No practical limit (64-bit chunk sizes) |
| Platform support | macOS 10.4+, iOS 5.0+ |
What is a CAF file?
CAF is Apple's audio container format, introduced in 2005 alongside Mac OS X 10.4 Tiger. It was built to replace aging formats like AIFF and WAV, which cap file sizes at 4 GB due to 32-bit size fields. CAF uses 64-bit chunk sizes, so a single file can hold as much audio as your storage allows.
CAF is a chunk-based container, meaning it wraps audio data along with descriptive and optional metadata in distinct labeled sections. The format is codec-agnostic: it can store PCM, AAC, MP3, FLAC, Opus, and other audio encodings inside the same wrapper. Apple defined the specification publicly, and it is supported natively across macOS and iOS through the Core Audio APIs. The format is also used internally by Apple's audio tools and professional audio apps on the Mac.
History
Apple released CAF with Mac OS X 10.4 in 2005 and published the formal specification document in March 2006. The format was designed specifically to address the 4 GB file-size ceiling of WAV and AIFF, which became a real problem for high-resolution, multi-channel audio recordings. iOS gained native CAF support in iOS 5.0, released in 2011, making it a common recording format on iPhone and iPad.
How it works
A CAF file starts with a short file header that identifies it as CAF and records the format version. After the header comes a series of chunks, each with a 4-byte type tag and a 64-bit size field followed by the chunk data. Every valid CAF file must contain an Audio Description chunk immediately after the header, which describes the codec, sample rate, and channel count, plus an Audio Data chunk holding the actual audio. Files with variable-bitrate audio (such as AAC or MP3) must also include a Packet Table chunk that records the byte size of every individual audio packet.
What it is used for
- Recording long, high-resolution audio sessions on macOS where WAV's 4 GB limit would be hit
- iOS app development where AVFoundation's default recording output is a CAF file
- Storing uncompressed multi-channel audio for music production and post-production on Apple platforms
- Archiving audio with embedded metadata such as channel layout, tempo, and loop points
How to open it
On macOS, CAF files open natively in QuickTime Player, GarageBand, Logic Pro, and most Core Audio-compatible apps. On other platforms, use VLC, FFmpeg, or convert the file to a more widely supported format such as WAV or MP3.
Pros and cons
Strengths
- No practical file-size limit thanks to 64-bit chunk sizes
- Codec-agnostic container that works with PCM, AAC, MP3, FLAC, and more
- Stores rich metadata including channel layout, loop points, and tempo markers
- Native, zero-overhead support across all Apple platforms via Core Audio
Trade-offs
- Poor support outside Apple platforms; most Windows and Linux players need FFmpeg or a plugin
- Not suitable for web delivery since browsers do not support audio/x-caf natively
- Less common than WAV or AIFF, so some third-party tools skip it entirely
- Files recorded on iPhone often need conversion before use in non-Apple software
Convert CAF files
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CAF FAQ
Can I play a CAF file on Windows?
Not without extra software. Windows Media Player and most standard Windows audio apps do not recognize CAF. Install VLC or use an online converter to turn it into MP3 or WAV first.
Why does my iPhone record in CAF format?
Apple's AVFoundation framework defaults to CAF when an app records audio without specifying an output format. It is the native container for Core Audio on iOS.
Is CAF lossless?
CAF is a container, not a codec. Whether the audio inside is lossless depends on how it was recorded. A CAF file holding 32-bit PCM is lossless; one holding AAC is lossy.
What is the difference between CAF and AIFF?
Both are Apple audio formats, but AIFF is limited to roughly 4 GB per file because it uses 32-bit chunk sizes. CAF uses 64-bit chunk sizes, supports many more codecs, and can store more types of metadata.