MP3, WAV, M4A and FLAC: which audio format to use

Audio formats divide into two groups. Lossless formats keep every sample of the original recording. Lossy formats permanently discard the parts of the signal that human hearing is least likely to notice, which is how they get small.

The four you will meet

• WAV is uncompressed and lossless. About 10 MB per minute in stereo. It is the working format for recording and editing, not for distribution.
• FLAC is compressed and lossless. Roughly half the size of WAV with identical audio. This is the right archive format.
• MP3 is lossy and universal. Nothing refuses to play it. At 192 kbps and above most listeners cannot distinguish it from the original on normal equipment.
• M4A, which contains AAC, is lossy and more efficient than MP3. Better sound at the same size, and the default on Apple devices and most modern video.

The rule that matters

Converting from lossless to lossy is a one way door. Once the data is discarded, converting the MP3 back to WAV does not restore it. You get a large file containing the same reduced audio. Keep a lossless original if the recording matters.

Converting between two lossy formats, for example M4A to MP3, decodes and re-encodes, which loses a little more each time. It is fine once. Do not do it repeatedly.

Practical choices

• Voice memo or interview to send: MP3. Small, plays everywhere.
• Music you own and want to keep: FLAC for the archive, MP3 or M4A for the phone.
• Recording you are still editing: WAV until you are finished.
• Audio pulled from a video: MP3 unless you plan to edit it, in which case WAV.

Extracting audio from video

Pulling the audio out of an MP4 does not re-record anything. The audio track is already inside the file, usually as AAC. Converting it to MP3 re-encodes once, which is acceptable for speech and fine for music at a reasonable bitrate. If you want no additional loss at all, extract to M4A instead, which can often keep the original track.