How to Convert M4A to FLAC

M4A is a lossy format. When the M4A file was originally created (from iTunes, Apple Music, a recording app, or a video export), some audio data was permanently discarded by the AAC encoder. Converting M4A to FLAC decodes the AAC audio and wraps the resulting PCM samples in a lossless FLAC container. The output is lossless in the sense that no further quality loss occurs from this conversion step. However, the audio quality ceiling is set by the original M4A bitrate — FLAC simply preserves it exactly. Think of it as: FLAC holds exactly what M4A had. Nothing more, nothing less.

The most common reason: you want a consistent archive format. If your collection mixes WAV, FLAC, M4A, and MP3, converting everything to FLAC creates a uniform lossless-or-best-available library. Another reason: compatibility. FLAC is open and supported natively by most Linux systems, many Android music players, and open-source software. M4A support requires Apple or MPEG-4 codec support. A third reason: re-encoding insurance. If you plan to compress the audio again (to MP3 or OGG for a different platform), keeping an intermediate FLAC avoids lossy-to-lossy transcoding at each step. Re-encode from the FLAC rather than from the M4A each time.

AudioUtils runs FFmpeg compiled to WebAssembly in your browser. The pipeline: the M4A container is opened locally, the AAC stream is decoded to raw PCM, and the PCM samples are encoded losslessly into a FLAC container. FLAC encoding is fast and lossless. The output FLAC will be larger than the M4A but smaller than an equivalent WAV. FLAC typically compresses PCM by 40–60%. No files are uploaded. The conversion runs in a browser Worker thread. M4A files are small, so conversion completes quickly — usually under 10 seconds for a typical song.

M4A (AAC at 256 kbps): approximately 2 MB per minute. FLAC (lossless): approximately 4–6 MB per minute (depending on audio content complexity). WAV (uncompressed): approximately 10 MB per minute. FLAC will be noticeably larger than the source M4A. This is expected — you are moving from compressed to losslessly compressed. The FLAC is still significantly smaller than WAV. For archival purposes where compatibility matters, FLAC is often preferable to WAV because of this size advantage while maintaining identical audio quality (the same quality that was in the M4A).

FLAC has broad modern support: Android: natively supported since Android 3.1. All major music apps play FLAC. Linux: supported by all major media players without additional codecs. Windows 10 and later: native FLAC support in Windows Media Player and Groove Music. DAWs: Logic Pro, Ableton Live, Reaper, and Pro Tools import FLAC. Browsers: Chrome and Firefox play FLAC natively in HTML5 audio. Safari supports FLAC in newer versions. Limitations: older Apple software (pre-macOS 11 Finder previews, older iTunes) may not play FLAC. For Apple-primary users, keeping the M4A is often more practical.

M4A uses iTunes atom tags. FLAC uses Vorbis Comment tags. FFmpeg handles the remapping during conversion: Artist, title, album, track number, year, and genre all transfer. Embedded album artwork typically transfers if present in the source M4A. Replay Gain tags, if present in the M4A, may not have FLAC equivalents and could be dropped. After conversion, check the metadata in your media player to verify the tags transferred correctly. Most common fields will be populated correctly. Unusual or extended tag fields from iTunes may not have exact FLAC equivalents.