Audio file formats

Which audio format should I use?

For music you want to play anywhere, MP3 at 192 kbps or higher still has no equal in compatibility. For the same size at slightly better quality, AAC is the modern choice and is what Apple Music, YouTube and most phones use by default.

For a collection you intend to keep, rip to FLAC. It is lossless, so it can be converted to any lossy format later without a second generation of quality loss, and it typically stores a CD at roughly half the size of the raw WAV.

For recording and editing, work in WAV or AIFF and only compress on export: repeatedly editing and re-saving a lossy file degrades it each time. For speech, calls and anything at a very low bitrate, Opus outperforms everything else.

Does converting between audio formats lose quality?

Converting from lossless to lossless (WAV to FLAC and back) loses nothing at all, which is the point of a lossless codec. Converting lossless to lossy (FLAC to MP3) discards detail once, which is normal and usually inaudible at a good bitrate.

The case to avoid is lossy to lossy, such as MP3 to AAC or a re-encoded MP3. Each pass throws away more, and the second encoder is working on damage the first one already did. Always convert from the highest-quality copy you still have.

How to tell what an audio file really is

Audio formats identify themselves in their first bytes. An MP3 with tags starts with the ASCII text ID3, a FLAC file starts with fLaC, a WAV starts with RIFF and has WAVE at offset 8, and an Ogg or Opus file starts with OggS. A file named .mp3 that starts with fLaC is a FLAC in disguise.

That matters because a wrong extension is the usual reason a player rejects an otherwise fine file. Drop it into the identifier on the home page to read the real signature in your browser, or open it in VLC and check Tools then Codec Information.

Compressed, lossless and uncompressed

Audio formats fall into three groups. Lossy compressed formats (MP3, AAC, OGG, Opus) discard sound information to shrink the file, which is inaudible at good bitrates and perfect for streaming and portable use. Lossless compressed formats (FLAC, ALAC) keep every bit of the original but still save space, so they suit archiving and high-fidelity listening. Uncompressed formats (WAV, AIFF) store raw samples, giving the largest files and the simplest data, favoured in recording and editing.

MP3 remains the most compatible format and plays on anything. AAC, used by Apple and YouTube, sounds better at the same bitrate. Opus is the modern champion for low-bitrate speech and streaming.

Codec or container?

As with video, some audio extensions are codecs and others are containers. An .m4a file, for example, is an MP4 container that usually holds AAC audio, while .ogg is a container that most often holds Vorbis or Opus. This is why the same extension can hold different underlying audio.