AIFF MIME Type

What does audio/x-aiff mean?

The audio/x-aiff media type is a widely used, unregistered identifier for Audio Interchange File Format files. AIFF is a chunk-based audio container created by Apple. It most often holds uncompressed linear PCM samples, so it is common in recording, editing, sample libraries, and interchange between audio applications.¹

The leading x- reflects an old convention for nonstandard identifiers. Neither audio/x-aiff nor the also-used audio/aiff currently appears in the IANA media type registry.² Modern IETF guidance discourages minting new names with an X- prefix, but existing software still needs to recognize established values such as audio/x-aiff.³

How to identify an AIFF file

AIFF belongs to the Interchange File Format family. The file begins with an IFF FORM chunk:

FORM alone is not enough to identify AIFF because other IFF formats use the same opening bytes. A detector must also check the form type at bytes 8 through 11. Inside an ordinary AIFF file, a COMM chunk describes the channels, sample frames, bit depth, and sample rate, while an SSND chunk carries the sound data.⁴

The usual extensions are .aif and .aiff. Apple identifies .aifc and .cdda with AIFF-C, a related form that can describe compressed encodings.⁵ An extension cannot tell you whether a particular decoder supports the encoding inside an AIFF-C file.

AIFF history and the AIFF-C extension

Apple published AIFF version 1.3 on January 4, 1989. The format adapted Electronic Arts' IFF chunk structure for sampled sound. AIFF is fully documented and does not require an external service or proprietary key to decode.¹

The original form was designed around PCM audio. AIFF-C followed in 1991 and added a compression-type field to the common chunk. Despite its name, AIFF-C is not necessarily compressed: its NONE compression code represents ordinary PCM, while other codes identify byte-swapped PCM, floating-point samples, A-law, mu-law, and other encodings.⁴

This distinction matters for interoperability. An application may advertise AIFF support but only decode uncompressed PCM. Adobe Audition, for example, documents support for all uncompressed AIFF files and most common compressed variants, not every possible AIFF-C encoding.⁶

How large is an AIFF file?

For uncompressed PCM, the audio payload size is predictable:

sample rate x bit depth / 8 x channel count x duration

One minute of stereo, 44.1 kHz, 16-bit PCM therefore uses about 10.6 MB before the small amount of chunk overhead. Doubling the bit depth or sample rate roughly doubles the payload size. AIFF does not improve or reduce PCM sound quality compared with a WAV file carrying identical samples. The formats arrange headers and byte order differently, but the decoded sample values can be the same.

How to open an audio/x-aiff file

AIFF remains well supported in professional audio tools:

• Apple Logic Pro imports AIFF and can export uncompressed projects as AIFF.⁷
• Adobe Audition opens .aif, .aiff, and .aifc, including uncompressed files with as many as 32 channels.⁶
• FFmpeg can both decode and encode Audio IFF files, making it useful for inspection and batch conversion.⁸

Web playback is less portable. Apple's archived Safari guide documents audio/aiff and audio/x-aiff for Safari on iOS, but AIFF is not one of the small set of formats developers can assume across all browsers.⁹ For a website, provide an AAC, MP3, Opus, or FLAC alternative and test the exact browser and operating system combination.

Support in Poly

Poly has an explicit audio/x-aiff type and recognizes the .aiff extension. It runs AIFF through the normal audio pipeline, which extracts duration and available tags, uses embedded artwork when present, creates audio-similarity segments, and transcribes spoken content to WebVTT. The transcript powers full-text search and lets poly file read and the Poly agent read what was said.

There are two practical limitations:

• Poly's filename inference currently maps .aiff, but not .aif or .aifc. A file detected from its bytes can still be classified as audio, but extension-only recognition is narrower than the format's common extension set.
• Poly's player uses the original file URL rather than a browser-friendly audio transcode. The preview can therefore fail when the browser cannot decode that AIFF or AIFF-C encoding.

The agent backend explicitly accepts AIFF and sends it as audio/aiff. It can also work from the stored transcript. For instrumental music, noise, or indistinct speech, audio similarity can remain useful even when the transcript is empty or inaccurate.

Converting AIFF without losing audio quality

Choose the output for the next workflow:

• WAV for a broadly compatible uncompressed editing or interchange file.
• FLAC for lossless compression and smaller storage, when the recipient supports it.
• AAC, MP3, or Opus for distribution where smaller files matter more than preserving every sample.

FFmpeg can make a lossless FLAC copy with:

ffmpeg -i input.aiff -c:a flac output.flac

To create a PCM WAV while preserving the decoded samples, select an output sample format that matches the source. Avoid changing sample rate or bit depth unless the destination requires it. Converting from AIFF to a lossy codec discards information, and converting that lossy result back to AIFF cannot restore it.

Is AIFF the same as WAV?

No. Both commonly carry uncompressed PCM and can preserve the same audio samples, but they are different containers. AIFF uses the big-endian IFF structure associated with Apple workflows. WAV uses Microsoft's little-endian RIFF structure. Renaming .aiff to .wav does not convert the container.

AIFF is still a sensible interchange or working format when the receiving audio application expects it. WAV is usually safer for broad cross-platform exchange, while FLAC is often preferable for lossless storage where compatibility permits.