.CAF File Format

Introduction

CAF is Apple’s audio file format for macOS and iOS, part of Core Audio. It was designed to replace AIFF and WAV inside Apple’s software: its sizes are 64-bit, so a file has no 4 GB limit, and it can hold any format Core Audio supports, from plain PCM to AAC and Apple Lossless.

Most CAF files met in practice hold uncompressed PCM, for example sound effects in apps and audio exported by Apple’s tools.

Structure

A CAF file starts with an 8-byte file header: the type caff, a 16-bit version (1) and 16-bit flags. Chunks follow, each a four-character type and a signed 64-bit size, all big-endian. The audio description chunk desc comes first and gives the sample rate (as a 64-bit float), the format ID, format flags, bytes and frames per packet, channels and bits per channel.

The audio data chunk data starts with a 4-byte edit count, then holds the audio. Its size may be −1 when it is the last chunk and its length was not known while recording. Formats with packets of varying size also need a packet table chunk pakt. Optional chunks carry the channel layout, markers, regions and text information.

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