The AIFF file (.aiff, .aif, .aifc)

AIFF is Apple's format for uncompressed audio, created in 1988 for the Macintosh and the Apple II. Like WAV, it stores sound as a plain list of samples, with nothing thrown away, so it's used for recording, editing and mastering. The Library of Congress describes it as widely adopted by Apple users in professional audio work, and functionally equivalent to WAV, which most Windows users choose.

Apple based AIFF on IFF 85, the Interchange File Format that Electronic Arts published in 1985, best known from the Amiga. That's where its chunk structure and its big-endian byte order come from: the Motorola 68000 processors in Macs and Amigas stored numbers that way.

The names you'll meet:

• .aiff and .aif: the same format. .aif is the older, three-letter form and still the most common.
• AIFF-C (.aifc): an extension from around 1991 that adds a compression type to the header. Despite the name, many AIFF-C files hold uncompressed audio, just in a different byte order or as floating-point numbers.

Every AIFF is a FORM chunk of type AIFF with chunks inside. Each chunk is a 4-character ID, a 32-bit size and the data; a chunk with an odd size gets a zero pad byte, not counted in the size, so the next one starts on an even offset. Only COMM is always required, and the order of chunks is free, although SSND usually comes last.

Samples are linear two's complement numbers, channels interleaved. Bit depths that aren't a whole number of bytes, such as 20 bits, are stored left-justified in the next whole size (3 bytes) with the unused low bits set to zero.

WAV stores the sample rate as a 32-bit whole number. AIFF stores it as a 10-byte IEEE 754 extended-precision float. It can describe any rate exactly, including fractional ones, but most programming languages have no 80-bit type, so every AIFF reader carries a few lines of code to convert it. For the usual rates, the bytes are:

The pattern is visible: the first two bytes are the exponent (16,383 plus the power of two), and the next bytes are the rate's binary digits, starting with a 1. That's why 22,050, 44,100 and 88,200 Hz share the digits AC 44 (44,100 is 0xAC44) and differ only in the exponent. To read it in code: take the 64-bit mantissa, divide by 2⁶³ and multiply by 2 to the power of (exponent − 16,383).

AIFF-C changes the form type to AIFC, adds the FVER chunk, and adds two fields to COMM: a 4-character compression type and a human-readable name. Here are the first chunks of the same four frames written by FFmpeg as little-endian AIFF-C:

46 4F 52 4D 00 00 00 50 41 49 46 43   FORM, 80 bytes, "AIFC"
46 56 45 52 00 00 00 04 A2 80 51 40   FVER: AIFC version 1
43 4F 4D 4D 00 00 00 18               COMM, 24 bytes
00 02 00 00 00 04 00 10               2 channels, 4 frames, 16 bits
40 0E AC 44 00 00 00 00 00 00         44,100 Hz
73 6F 77 74                           compression type "sowt"
00 00                                 name: empty, plus a pad byte
53 53 4E 44 00 00 00 18 …             SSND, then 00 00 01 00 80 00 …

The sowt variant arrived with Apple's move to Intel processors, which, like today's Apple silicon, are little-endian, so samples can be used without byte-swapping. Older or simpler readers that only know plain AIFF may reject these files, even with an .aif extension. ffprobe shows the type: codec_tag_string=sowt, codec_name=pcm_s16le.

AIFF and WAV store the same thing: for the same bit depth and sample rate, the sound is identical and the files are almost the same size. Converting between them is lossless. The differences are in the packaging:

For archiving or sharing without loss, FLAC gives the same samples in a smaller file, with much better tag support. In Apple's world, ALAC in an M4A file does the same job. For listening, an MP3 or AAC copy is around a tenth of the size.

• It downloads instead of playing in the browser: Chrome and Firefox don't play AIFF (we checked Chrome 141 and Firefox 142), and it isn't one of the web's standard media formats. Convert to WAV, MP3 or M4A for a web page.
• "Unsupported compression" for an .aif file: it's really AIFF-C, often sowt or fl32. Check with ffprobe and convert it to plain 16- or 24-bit AIFF or WAV.
• Loud static instead of sound: a program read big-endian samples as little-endian (or the reverse), typically when importing raw data or with a hand-written reader that ignores sowt. Import with the correct byte order.
• Titles and artwork lost after converting: AIFF's text chunks and ID3 chunks are read by some apps and ignored by others. Re-tag after converting, or use FLAC or M4A when metadata matters.
• A very long recording won't open: it may have passed 2 GB. Record long sessions as CAF or RF64 WAV, or split them.
• Python can't open it: the standard library's aifc module is gone in Python 3.13. Use soundfile or pydub, or convert first.

• Mac: double-click it: QuickTime Player and Music play it, and Finder's Quick Look previews it. Logic Pro can record in AIFF, WAVE (BWF) or CAF, and GarageBand exports songs as AAC, MP3, AIFF or WAVE.
• Windows and Linux: VLC and foobar2000 play AIFF; Audacity opens, edits and exports it.
• Phones: VLC plays AIFF on Android and iOS.
• Inspect it: ffprobe file.aif shows the form (AIFF or AIFF-C), codec, sample rate and tags.

# AIFF to WAV, losslessly (16-bit stays 16-bit)
ffmpeg -i in.aif -c:a pcm_s16le out.wav

# WAV to AIFF
ffmpeg -i in.wav -c:a pcm_s16be out.aiff

# AIFF to FLAC (lossless, smaller) or MP3
ffmpeg -i in.aif out.flac
ffmpeg -i in.aif -c:a libmp3lame -q:a 2 out.mp3

# on a Mac, with Apple's own tool
afconvert -f WAVE -d LEI16 in.aif out.wav

Match the codec to the source's bit depth: use pcm_s24le (WAV) or pcm_s24be (AIFF) for 24-bit files, or the conversion will reduce them to 16 bits.