How to Convert AIFF to FLAC

AIFF is a lossless uncompressed format. FLAC is a lossless compressed format. Both store audio with zero quality loss, but FLAC uses a mathematically reversible compression algorithm to reduce file size. For a typical CD-quality track (44.1 kHz, 16-bit stereo): AIFF is about 10 MB per minute. FLAC is about 4–6 MB per minute — a 40–60% reduction with identical audio. Beyond file size, FLAC has better cross-platform support than AIFF. Windows, Linux, and Android all play FLAC natively without Apple's QuickTime codec. For building a cross-platform lossless archive, FLAC is generally preferable to AIFF.

AIFF uses the RIFF/IFF container structure and stores PCM audio directly — no compression. Developed by Apple in 1988, it remains the native lossless format in Logic Pro and other Apple audio software. FLAC (Free Lossless Audio Codec) uses its own container and applies prediction-based lossless compression to PCM data. Developed by the Xiph.Org Foundation and released in 2001, it is open-source and patent-free. Both support up to 32-bit depth and sample rates up to 655 kHz. Both support embedded metadata. FLAC has built-in MD5 checksums for verifying file integrity — a significant advantage for archival use. AIFF supports embedded pictures (album art) as standard; FLAC does too via its PICTURE metadata block.

AudioUtils uses FFmpeg compiled to WebAssembly. The pipeline is: read the AIFF container locally, extract the PCM samples, apply FLAC lossless encoding, and write the output FLAC file. Since both input and output are lossless, the audio data is mathematically identical before and after conversion. The compression is reversible — any FLAC decoder can reconstruct the exact PCM samples that were in the AIFF. AIFF files are large, so processing takes longer than for compressed source formats. A 50 MB AIFF file typically takes 15–40 seconds to convert to FLAC in the browser, depending on CPU speed and FLAC compression level.

FLAC offers compression levels from 0 (fastest, largest) to 8 (slowest, smallest). The compression level affects only file size and encoding time — not audio quality, which is always lossless. Level 0: fast encoding, ~35% smaller than AIFF. Level 5 (default): moderate time, ~50% smaller than AIFF. Best all-purpose setting. Level 8: slowest, ~55% smaller than AIFF. Marginal improvement over level 5. For archival, level 5 or 6 gives the best balance. The difference between level 5 and level 8 is typically only 3–5% in final file size, not worth the extra encoding time in most workflows. Decoding speed is identical at all compression levels.

AIFF stores metadata in ID3 chunks or Apple-specific AIFF chunks. FLAC uses Vorbis Comment blocks. FFmpeg maps standard fields during conversion: Title, artist, album, track number, year, and genre transfer reliably. Album artwork embedded in the AIFF transfers as a FLAC PICTURE block. Logic Pro-specific markers, loop regions, and tempo data will not have FLAC equivalents and are dropped. For critical archival conversions, verify the FLAC metadata after conversion. Play the FLAC file in a player that shows metadata and compare against the original AIFF. Add any missing fields manually.

FLAC is more broadly compatible outside the Apple ecosystem: Windows 10+: native FLAC support in File Explorer, Windows Media Player, and Groove Music. Android: all major music apps support FLAC. Linux: universal support. DAWs: Logic Pro, Ableton, Pro Tools, Reaper, and FL Studio all import FLAC. Browsers: Chrome and Firefox play FLAC natively. AIFF limitations: natively decoded only by Apple software and players with QuickTime. Windows and Linux require codec installations for AIFF. For a long-term archive that you want to be accessible on any system in 10+ years, FLAC is the safer choice over AIFF. It is open, well-supported, and has integrity checking built in.