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WAV, AIFF, FLAC, MP3, AAC and Opus: which audio format to deliver where
Six audio formats cover almost everything a musician sends or receives. Here is what each one is, which are lossless and which throw data away, and a simple rule for what to deliver to a distributor, a collaborator or a listener. Sources checked on 27 Oct 2026.
Key facts
- WAV (Microsoft and IBM, 1991) and AIFF (Apple, 1989) are containers that usually hold uncompressed PCM audio; the Library of Congress calls them functionally equivalent.
- FLAC is lossless compression: the original audio can be fully restored. Spotify says FLAC is strongly preferred for delivery and WAV is accepted if it meets the same requirements.
- MP3, AAC and Opus are lossy. Opus scales from 6 kbit/s speech to 510 kbit/s stereo music, per its IETF standard, RFC 6716.
An audio file format is the way a recording is stored on disk: either every sample kept exactly (lossless), or a smaller file that drops what a listening model says you won't hear (lossy). Pick the wrong one at the wrong moment and you either bloat a hard drive or, worse, bake permanent damage into a master.
Six names cover almost everything a musician touches. This guide sorts them into two piles and ends with a delivery rule. For the numbers inside the file, see sample rate and bit depth explained.
The lossless pile: WAV, AIFF, FLAC
WAV was specified by Microsoft and IBM in August 1991 as part of RIFF for Windows 3.1, according to the Library of Congress format description. It is a container; the audio inside is usually uncompressed linear PCM. The classic format tops out around 4 GB, which is why extended variants such as RF64 exist for very long multitrack recordings.
AIFF is Apple's equivalent, with its main specification dated January 1989. The Library of Congress calls WAV "functionally equivalent" to it, noting AIFF is common among Apple users in professional audio. In practice: same audio, different wrapper. Choose whichever your DAW and collaborators prefer.
FLAC compresses audio "without any loss in quality", so the original can be fully restored, says the Xiph.Org project page. It is non-proprietary and unencumbered by patents. Think of it as a zip file built for audio: smaller than WAV, bit-for-bit the same when decoded.
The lossy pile: MP3, AAC, Opus
MP3 is Layer III of the MPEG-1 and MPEG-2 audio standards. It uses perceptual coding to discard less audible detail; a 128 kbit/s MP3 is roughly 1/11 the size of CD audio, per the Library of Congress. Its patents expired in 2017, which is part of why it is still everywhere.
AAC is defined in Part 3 of the MPEG-4 standard. The Library of Congress notes it is generally judged significantly better than MP3 at the same data rate, and it has long been the format of Apple's iTunes store.
Opus is the youngest, standardised by the IETF in RFC 6716. It was designed for interactive use such as voice calls and in-game chat, with algorithmic delay from 5 to 65.2 ms, yet it scales from 6 kbit/s speech to 510 kbit/s stereo music.
What to deliver where
| Where it's going | Send | Why |
|---|---|---|
| Distributor / streaming services | FLAC, or WAV that meets the spec | Spotify says FLAC is "strongly preferred" and converts WAV to FLAC itself |
| Mix or mastering engineer | WAV or AIFF at session rate and bit depth | Universal, no decode step, lossless |
| Archive of your masters | FLAC or WAV | Lossless; FLAC saves space |
| Quick demo or feedback link | MP3 or AAC at a high bitrate | Small, plays anywhere |
| Live collaboration, calls, low-latency streams | Opus | Built for low delay |
For streaming delivery, the specifics matter. Spotify's audio file formats page asks for stereo, 44.1 kHz or higher at the native rate, and 24-bit if that is the native master, with one master per track. WAVs must use the plain PCM format code (0x0001), not WAVE_FORMAT_EXTENSIBLE. Spotify losslessly converts WAV to FLAC and reduces anything above 24-bit to a maximum of 44.1 kHz/24-bit, and asks you not to do these conversions yourself.
What we think
The single most common mistake we see is not choosing the "wrong" lossless format; WAV, AIFF and FLAC are interchangeable for audio. It is letting a lossy file slip into the chain: a sample pulled from an MP3, a reference bounced to AAC and then re-imported, a "master" that is really a decoded MP3 saved as WAV. Once data is thrown away, no later format brings it back, and each lossy re-encode stacks its own artefacts on top. That is an inference from how perceptual coding works, not a measured result, but it is why our rule is blunt: lossless until the very last hop to the listener, and never encode lossy twice.
The other point worth making is that the WAV-versus-FLAC argument is mostly over. A major streaming service now says it prefers FLAC and converts WAV to it anyway. If your distributor accepts FLAC, sending it saves upload time and loses nothing. Keep WAV for the studio, where every tool opens it without thinking.
Sources
- Audio file formats, Spotify for Artists (primary source). Accessed 27 Oct 2026.
- FLAC - Free Lossless Audio Codec, Xiph.Org Foundation (primary source). Accessed 27 Oct 2026.
- RFC 6716: Definition of the Opus Audio Codec, IETF (primary source). Accessed 27 Oct 2026.
- WAVE Audio File Format, Library of Congress. Accessed 27 Oct 2026.
- AIFF (Audio Interchange File Format), Library of Congress. Accessed 27 Oct 2026.
- MP3 (MPEG Layer III Audio Encoding), Library of Congress. Accessed 27 Oct 2026.
- AAC_MP4 (MPEG-4 Advanced Audio Coding), Library of Congress. Accessed 27 Oct 2026.
Researched with AI assistance, written and checked by WATMM Desk.