Two kinds of M4A, two different results
The M4A extension hides an important detail. Most M4A files contain AAC, a lossy codec. Some contain ALAC, Apple's lossless codec, which iTunes users often chose when ripping CDs. Converting M4A to FLAC means something very different in each case, so the converter displays the codec of every file.
| Inside the M4A | What FLAC gives you | Size change |
|---|---|---|
| ALAC (Apple Lossless) | a true lossless copy, identical audio | about the same size |
| AAC (lossy) | an exact copy of the decoded AAC, no improvement | three to six times larger |
Moving an Apple Lossless library
This is the main reason for the conversion. People who ripped their CDs to ALAC in iTunes and now use Android phones, Linux, a network player, Plex, Jellyfin or a hi-fi streamer find that FLAC is much more widely supported. ALAC and FLAC compress about equally well, so the library will need roughly the same space. Both are lossless, so you can convert in either direction without losing anything. Keep the bit depth the same as the ALAC file, 16-bit for CD rips, 24-bit for hi-res downloads, and the sample rate unchanged.
Tags carry over
Title, artist, album, album artist, track and disc number, year and genre are copied into FLAC Vorbis comments, so your library stays organised in the new player. Embedded cover art is copied into the FLAC file as well. Drop whole albums at once to convert them in a batch.
AAC files: think twice
If the M4A contains AAC, for example an iTunes Store purchase at 256 kbps or a voice memo, converting it to FLAC only makes sense when a program or library strictly requires FLAC. The sound will be exactly the same as the M4A, and the file several times larger. For playback on non-Apple devices, M4A to MP3 or M4A to OGG keeps files small. Songs downloaded inside the Apple Music app are DRM-protected and cannot be converted at all. To check whether a file was originally lossless, look at its frequency range with the spectrum analyzer.