MP3 vs AAC vs Opus vs FLAC vs WAV: Audio Formats Explained

A lossless file can be decoded back to exactly the audio that went in, like a ZIP file for sound. A lossy file cannot: the encoder uses a psychoacoustic model to discard detail, and that detail is gone for good. Converting a lossy file to a lossless format does not restore anything; an MP3 turned into a WAV is simply a much bigger file that sounds exactly like the MP3. Each additional lossy re-encode can add small artefacts, so keep a lossless or original copy if you expect to edit later.

MP3 dates from the early 1990s and plays on practically everything, from car stereos to smart speakers. Its patents have expired, so it is free to use. At 192 to 320 kbps most listeners cannot distinguish a well-encoded MP3 from the original on most music; at 128 kbps artefacts become noticeable on cymbals and complex passages.

Choose MP3 when the priority is that the file plays anywhere, for example podcasts, audiobooks for older players or music for a car USB stick.

AAC was designed as MP3's successor and generally sounds better at the same bitrate. It is the standard audio codec in MP4 video, the format of .m4a files, and what Apple Music and many streaming services use. Support is excellent on phones, browsers and modern car systems, though a few very old devices only understand MP3.

For music, 192 to 256 kbps AAC is a common high-quality choice; 128 kbps is fine for speech. If you are extracting audio from a phone video, the audio is very likely AAC already.

Opus is an open, royalty-free codec standardised by the IETF in 2012. It adapts from low-bitrate speech to high-quality music and has very low latency, which is why it is used in WebRTC video calls and many voice chat apps. At the same bitrate it generally matches or beats AAC, particularly below about 128 kbps.

Opus is stored in .opus, .ogg, WebM or MKV files. Browsers and Android support it well, and recent Apple software can play it, but some older players and car systems cannot. It is ideal for voice recordings, web audio and anywhere small size matters.

FLAC stores audio losslessly but compresses it, typically to somewhere around half to two-thirds of the uncompressed size depending on the material. It supports tags and cover art, and it is the standard format for lossless music downloads and CD rips.

FLAC is the right format for archiving and for any music you may convert again later, because you can always make an MP3 or AAC from it without stacking generational loss. Apple's equivalent is ALAC, usually stored in .m4a files.

WAV usually holds raw PCM audio with no compression at all. CD-quality stereo (44.1 kHz, 16-bit) runs at about 1,411 kbps, roughly 10 MB per minute. Every audio editor opens WAV instantly and there is no decoding cost, which is why it is the working format in studios. AIFF is Apple's near-identical equivalent.

WAV is a poor format for sharing or storing large libraries because of its size, and its metadata support is weaker than FLAC's.

A practical cheat sheet:

• Maximum compatibility: MP3 at 192 to 320 kbps.
• Music on phones and modern devices: AAC (M4A) at 192 to 256 kbps.
• Voice notes, podcasts and web audio where size matters: Opus at 32 to 96 kbps.
• Archiving music or CD rips: FLAC.
• Editing and production: WAV (or AIFF on a Mac).

The Audio Converter converts between MP3, WAV, FLAC, AAC, M4A, OGG, Opus, AIFF and AC-3 in your browser. You choose the codec where the format offers more than one, the sample rate, and the bitrate as a percentage of the source's. For common jobs, WAV to MP3, FLAC to MP3 and M4A to MP3 have the output preselected. If the audio is inside a video, see how to extract audio from a video.