How to Convert FLAC to M4A

FLAC is not natively supported by Apple software. iPhones, iPads, Apple Music, and older versions of iTunes do not play FLAC files without third-party apps. M4A (which contains AAC audio) is Apple's preferred compressed format and plays natively across all Apple devices and software. If you maintain a FLAC archive of your music and want a copy optimized for Apple device storage or iTunes library management, converting to M4A is the standard approach. M4A also offers smaller file sizes than FLAC — a 35 MB FLAC track becomes roughly 5–8 MB as M4A at 256 kbps — while maintaining excellent audio quality at that bitrate.

M4A and AAC are closely related. AAC (Advanced Audio Coding) is the audio codec. M4A is a file extension for an MPEG-4 container that holds AAC audio. Think of it this way: AAC describes how the audio is compressed. M4A describes the container (file wrapper) holding that compressed audio. All M4A files contain AAC audio. Files with the .aac extension use a different, simpler container (ADTS) for the same AAC codec. For Apple device compatibility, M4A is the better-recognized extension. iTunes and Apple Music display M4A files correctly with full metadata support.

AudioUtils runs FFmpeg in WebAssembly inside your browser. The pipeline: FFmpeg decodes the FLAC stream to PCM, encodes the PCM using the AAC encoder, and wraps the output in an MPEG-4 (M4A) container. The entire process happens locally. FLAC files are lossless, so the decoding step is mathematically exact. The quality loss occurs in the AAC encoding step — the degree of loss depends on the bitrate you select. FLAC files are often large (20–50 MB per song). Conversion takes a bit longer than for compressed source formats, but most tracks complete in under 30 seconds on modern hardware.

Since you are converting from a lossless FLAC source, you have full quality to work with. Choose the AAC bitrate based on intended use: 128 kbps — casual listening, background music, voice content. Good quality, small files. 192 kbps — general music listening on earbuds or headphones. Most listeners find this transparent. 256 kbps — high-quality music, audiophile listening, Apple Music standard. Excellent quality. 320 kbps — maximum standard bitrate. Very small audible difference over 256 kbps for most content. Apple Music uses 256 kbps AAC for its catalog. Matching this bitrate for personal FLAC conversions ensures quality parity with the streaming service.

FLAC uses Vorbis Comment tags. M4A uses iTunes-style atom tags (MP4 metadata). These are different systems, but FFmpeg remaps common tags during conversion: FLAC TITLE becomes M4A title atom. FLAC ARTIST becomes M4A artist atom. FLAC ALBUM becomes M4A album atom. FLAC TRACKNUMBER becomes M4A track number. FLAC DATE becomes M4A year. After conversion, the M4A file displays correct metadata in iTunes, Apple Music, and iOS. Embedded album artwork transfers if present in the source FLAC. Some less common FLAC tags (like REPLAYGAIN data) may not have M4A equivalents and will be dropped during conversion.

For Apple device use, M4A (AAC) is the better choice over MP3: AAC achieves better quality than MP3 at the same bitrate. At 128 kbps, AAC sounds noticeably cleaner. M4A has full metadata support on Apple platforms — artwork, track numbers, playlists all work properly. Apple devices optimize AAC playback for battery efficiency. For non-Apple distribution or maximum compatibility: MP3 is the safer choice, as older devices and some car stereos only support MP3. For personal Apple device libraries converted from FLAC masters: M4A at 256 kbps is the standard recommendation.