Convert M4A to FLAC Online
Wrap your M4A (AAC) audio in a FLAC container. Free, in your browser, no file uploads.
.m4a · up to 100 MB
What you can do
M4A to FLAC: container compatibility with no quality gain
DAW compatibility
Some DAWs and audiophile players only accept FLAC for import. This conversion resolves the incompatibility.
100% private
Your music files never leave your device. Local processing without servers.
No quality improvement
Honesty first: the resulting FLAC contains the same compressed AAC audio. It does not recover lost quality.
Library migration
Unify your collection in a single container format for managers like Roon, Plex, or beets.
How it works
Three steps, no hassle
Upload your M4A file
Drag or select your .m4a file. No signup or installs required.
Browser-side processing
The AAC audio from your M4A is decoded and re-encoded to lossless FLAC codec in the FLAC container, entirely on your device.
Download your FLAC
FLAC file compatible with audio players, DAWs, and music libraries that only accept the FLAC container.
FAQ
Got questions?
No. This is the most important clarification: M4A (AAC) audio is a lossy format. When converted to FLAC, the destination codec is lossless, but that does not recover the information the AAC algorithm discarded during the original compression. The result is a FLAC file containing exactly the same audio as the M4A, with the same AAC compression artifacts faithfully preserved. It is analogous to taking a photo on a phone, printing it at high resolution, and scanning it again: the print is perfect, but the original camera pixels do not increase. If you have the uncompressed source file (WAV, AIFF) or the original FLAC, use that instead; if you only have the M4A, the resulting FLAC has exactly the same quality.
There are several valid scenarios. First, compatibility with players and DAWs: some audiophile-oriented music players (like Audirvana, Roon, or network players like Cambridge Audio StreamMagic) accept FLAC but have limited or no support for M4A/AAC. Second, library migration: when moving from an Apple ecosystem (iTunes/Music with M4A) to an agnostic one, having everything in FLAC simplifies integration with software like MusicBrainz Picard, beets, or Plex. Third, format normalization: if your workflow requires a single container format for your entire collection, converting M4A files to FLAC creates uniformity even without quality gain.
A FLAC file wrapping originally AAC audio is considerably larger than the M4A. iTunes AAC at 256 kbps takes roughly 2 MB per minute of audio. When decoded to uncompressed PCM and re-compressed with FLAC, the typical size is 20–35 MB per minute (comparable to a FLAC from a high-quality recording), because FLAC compresses PCM but is far less efficient than AAC at storing complex audio signals. Expect the FLAC to be 8 to 15 times larger than the original M4A.
M4A metadata is stored in the iTunes/MP4 tag format (ilst atoms: ©nam for title, ©ART for artist, etc.). FLAC uses the Vorbis Comment system (plain-text tags: TITLE, ARTIST, ALBUM, etc.). Conversion maps equivalent tags between both systems, and most converters including FFmpeg correctly transfer title, artist, album, year, genre, and track number. Embedded artwork in M4A (JPEG files inside the covr atom) is also transferred to FLAC's PICTURE block in most implementations. Proprietary iTunes tags without a Vorbis Comment equivalent may not be transferred.
AAC (Advanced Audio Coding) is the audio compression codec, published as an ISO standard in 1997 and developed by Fraunhofer IIS, Dolby, Sony, and AT&T. M4A is a file container: specifically, it is the MPEG-4 Part 14 format (ISO 14496-14) with the .m4a extension used by Apple to distinguish audio-only files from M4V video files. The audio inside an M4A can be AAC (most common), Apple Lossless (ALAC), or in rare cases HE-AAC. When speaking of 'converting M4A to FLAC', you are technically converting the AAC codec to the FLAC codec, changing both the codec and the container.
Exactly. The FLAC resulting from a conversion from lossy AAC M4A sounds bit-for-bit identical to the M4A (within the precision of FLAC decoding and re-encoding). The only benefit is compatibility with software that requires FLAC. If the goal is to improve audio quality, the only real solution is to obtain the recording in a lossless format from the source: CD FLAC, SACD, HD lossless download (Bandcamp FLAC, Qobuz FLAC). No post-processing exists that can recover information discarded by a lossy codec.
Convert M4A to FLAC: container compatibility without recovering AAC quality
The M4A format is the file extension used by Apple for audio files in the MPEG-4 Part 14 container (ISO 14496-14, published in 2003), visually distinguishing them from M4V video files. Internally, a typical M4A file from the iTunes Store or Apple Music service contains audio compressed with the AAC (Advanced Audio Coding) codec, an ISO standard from 1997 developed by Fraunhofer IIS, Dolby, Sony, Nokia, and AT&T as the successor to MP3. AAC is a lossy codec: during compression, the algorithm analyzes the frequency spectrum of the audio and discards information that psychoacoustic models predict the human ear will not perceive, reducing file size by up to 10 times compared to uncompressed PCM. At 256 kbps, Apple Music's AAC offers subjectively indistinguishable quality from the source for most listeners in a double-blind test, but the information discarded during encoding cannot be recovered under any circumstances. FLAC (Free Lossless Audio Codec), developed by Josh Coalson and released in July 2001 under the BSD license, is a lossless compression codec: it compresses PCM using linear prediction (LPC) and Rice-Golomb coding, reducing size by 40–60% compared to uncompressed WAV while preserving every sample exactly and allowing bit-perfect reconstruction of the original PCM. Converting M4A to FLAC decodes the AAC to PCM and then re-compresses that PCM with FLAC: the result is a lossless file containing exactly the audio that was in the M4A, with all its AAC compression artifacts intact. The fundamental rule is: FLAC is lossless relative to the PCM it was built from, not relative to the original audio before the initial AAC compression.
The most common question about this conversion — 'does it improve quality?' — deserves a detailed technical answer. The AAC compression process applies three main information-reduction techniques: the 1024-point MDCT (Modified Discrete Cosine Transform) filter bank that transforms the audio from the time domain to the frequency domain, the psychoacoustic masking model that calculates which frequencies are 'masked' by louder ones (Zwicker's simultaneous and temporal masking effect, published in full in 'Psychoacoustics: Facts and Models', 1990), and adaptive quantization that assigns fewer bits to less perceptible frequencies. Once this process is applied, the eliminated information does not exist anywhere in the M4A file and cannot be mathematically inferred. When converting to FLAC, the AAC is decoded to a PCM that contains only the information that survived the lossy compression, and that PCM is reversibly compressed with FLAC. The result: a larger file that perfectly preserves the already-degraded audio, adding and recovering nothing. In spectral analyses using tools like Spek or Audacity's spectrum analyzer, FLAC files converted from AAC show the characteristic frequency 'ceiling' above which no energy exists (typically around 16–20 kHz for AAC at 128–256 kbps), an unmistakable sign of lossy origin. This contrasts sharply with a native FLAC generated from a CD WAV or HD mastering, which shows spectral energy extending to 22 kHz without artificial discontinuity. Tools like Spek or the Aucdtect plugin for foobar2000 can automatically detect whether a FLAC originates from a lossy source by analyzing the statistical distribution of spectral energy, being particularly accurate at identifying AAC origin from the characteristic high-frequency cutoff pattern and the absence of natural pre-echo energy above the lossy codec's encoding ceiling.
Despite not improving audio quality, M4A to FLAC conversion has legitimate applications in music production workflows and digital library management. The most important is compatibility with professional software: several DAWs including REAPER in its standard configuration, some audio analysis plug-ins, and hi-fi network players like Cambridge Audio StreamMagic, Naim Uniti, or Linn DS systems accept FLAC as an import format but have limited support for M4A/AAC, especially on older firmware versions or when files are served from a NAS via UPnP/DLNA. For users migrating from an Apple ecosystem — where iTunes and Apple Music have used M4A as their native format since 2003 — to an agnostic music manager platform (Roon, Plex Music, Jellyfin, beets), having the entire library in FLAC simplifies indexing, automatic tagging with MusicBrainz Picard, and compatibility with high-end portable players like FiiO, Astell&Kern, or HiBy. The conversion is also useful when long-term file integrity verification via FLAC's built-in MD5 checksums is needed, or when the destination file system or transfer protocol has difficulties with the .m4a extension. Convertir.ai performs all conversion in the browser via WebAssembly, without sending files to any server, which is especially relevant for personal music collections where privacy is a priority. No file is uploaded to any external server at any point in the conversion process, and the tool works entirely offline once the page has loaded — making it suitable for use in restricted network environments or on flights. There are no conversion limits, no account required, and no watermarks or metadata changes introduced by the tool beyond the container format change itself.