Know what is inside your M4A first
M4A is an MPEG-4 audio container, and it can hold two very different codecs. Most M4A files, including iTunes Store purchases and many phone recordings, contain AAC, a lossy codec usually at 128 to 256 kbps. Others contain ALAC, Apple Lossless, which Apple released in 2004 and made open source in 2011.
FLAC (Free Lossless Audio Codec) was created by Josh Coalson in 2001 and is maintained by the Xiph.Org Foundation. It compresses audio without discarding anything, typically to 50 to 70% of the WAV size, so CD-quality FLAC is around 5 to 7 MB per minute.
Which codec your M4A uses decides what this conversion can and cannot do.
Does M4A to FLAC improve quality?
If your M4A is AAC, no. AAC is lossy, and the detail it removed is gone. Converting AAC M4A to FLAC stores the decoded audio perfectly, so it freezes the current quality and prevents further loss, but it cannot add anything back. The FLAC will be several times bigger and sound the same.
If your M4A is ALAC, this is lossless to lossless. The audio is decoded exactly and written as FLAC. One caveat: AudioDrop writes 16-bit FLAC, so a 24-bit ALAC file is reduced to 16-bit. The sample rate is kept.
M4A vs FLAC comparison
| Feature | M4A (AAC) | M4A (ALAC) | FLAC |
|---|---|---|---|
| Compression | Lossy | Lossless | Lossless |
| Typical size per minute | ≈ 1.9 MB at 256 kbps | ≈ 5 to 7 MB (CD quality) | ≈ 5 to 7 MB (CD quality) |
| Open format | No (licensed codec) | Yes, since 2011 | Yes |
| Plays natively on | Apple devices, Android, most players | Apple devices, some players | Android, Windows, Linux, most hi-fi players; recent macOS and iOS |
| Best for | Portable listening | Apple lossless libraries | Archiving and cross-platform lossless libraries |
Why people convert M4A to FLAC
If your only goal is better sound from AAC files, this conversion will not deliver it. Find the lossless original instead.
- Moving an Apple Lossless library to a non-Apple player, NAS or streamer that prefers FLAC.
- A DAW, DJ app or media server that handles FLAC more reliably than M4A.
- Standardising a mixed collection on one lossless format.
- Editing AAC audio repeatedly without adding a new lossy generation each time you save.
Settings and output
FLAC is lossless, so there is no bitrate or quality setting. Output is 16-bit at the source sample rate, encoded with AudioDrop's own FLAC encoder. File size depends on how complex the music is: quiet, sparse recordings compress more than dense rock or electronic tracks.
Album art, artist and track tags may not all be carried across from the M4A, so check your library after converting.
Moving an Apple library to FLAC
If you are migrating from Apple Music to a streamer, NAS or Android phone, start by sorting your M4A files by type. Apple Lossless files are worth converting to FLAC, because you keep full CD quality and gain wide support across non-Apple players.
AAC files are a different decision. Converting them to FLAC multiplies their size by three or four with no gain in sound. For most people, converting AAC M4A to MP3 or simply keeping the M4A files is more sensible. Convert AAC to FLAC only when your software requires lossless input or you plan to edit and re-save the audio many times.
Test a few tracks first and check that tags and artwork appear as you expect in your new player before converting the whole library.
No upload, works offline
This M4A to FLAC converter runs inside your browser using WebCodecs and WebAssembly. Your files are read from your device and the FLAC files are written back to it. Nothing is uploaded and no account is needed.
The page keeps working offline once loaded. Drop a full album and the tracks convert in parallel, each downloading individually. There is no fixed size cap, only your device's memory.