Convert FLAC to AAC Online
Convert lossless FLAC to high-quality AAC for streaming and Apple devices. Free, in your browser, no file uploads.
.flac · up to 100 MB
What you can do
FLAC to AAC: the best possible AAC quality from a lossless source
Lossless source
FLAC ensures the AAC encoder works with complete audio, free of prior compression artifacts.
Apple native
AAC is the native codec for iPhone, iPad, Apple Music, and iTunes. Hardware decoding.
100% private
Conversion happens in your browser. Your audio is never uploaded to any server.
Instant
No queues or waiting. Direct conversion in your browser in seconds.
How it works
Three steps, no hassle
Upload your FLAC file
Drag or select your .flac file. Up to 200 MB, no signup required.
FLAC → AAC encoding
FLAC is decoded to PCM and re-encoded to AAC following the optimal chain: lossless source → lossy codec. Maximum output quality guaranteed.
Download your AAC
Get an AAC file compatible with iPhone, iPad, Apple Music, iTunes, and any modern player.
FAQ
Got questions?
The difference is technically significant and practically important. When you convert MP3 to AAC, you apply a second lossy encoding on audio that already suffered the first (MP3). MP3 artifacts (high-frequency aliasing, spectral smearing, quantization noise) are embedded in the audio before the AAC encoder performs its own information reduction process. The result is an accumulation of artifacts from two generations of loss. In contrast, converting from FLAC means the AAC encoder works with complete, undegraded PCM audio — exactly as if you were encoding from the original CD. The difference is most audible at low bitrates (128 kbps or below), where the AAC encoder must make more aggressive decisions about what information to discard.
The answer depends on the intended use. For Apple Music and high-quality streaming platforms, 256 kbps AAC-LC is the standard Apple uses internally and is considered transparent (indistinguishable from the original in blind listening tests for most listeners). For personal storage on iPhone with limited space, 192 kbps AAC-LC offers excellent quality. For podcasts and voice content, 128 kbps mono AAC-LC is more than sufficient. The key point is that starting from FLAC, any of these bitrates represents the best possible quality for that bitrate, because the encoder works with the complete source.
If you only have the MP3 and not the FLAC, using the MP3 as source is the only option. But if you have both, always start from FLAC. The reason is the encoding chain: each lossy compression step permanently discards information. Converting FLAC → AAC is a single generation of loss. Converting MP3 → AAC is two accumulated generations. The improvement is most noticeable in recordings with heavy high-frequency content (cymbals, strings, granular synthesis) and in conversions to bitrates below 192 kbps.
Yes. AAC is Apple's native audio codec since QuickTime 6.0 (2002) and the iTunes standard format since its launch in 2003. All Apple devices (iPhone, iPad, Mac, Apple Watch, Apple TV, AirPods, HomePod) decode AAC in hardware, which means lower battery consumption than software decoding. Apple Music distributes its entire catalog in 256 kbps AAC. The container format for AAC in the Apple ecosystem is M4A (for audio) or MP4 (if it includes video), but the underlying codec is always AAC-LC or AAC-HE for voice-optimized or low-bandwidth content.
Yes, inevitably, because AAC is a lossy codec. FLAC (Free Lossless Audio Codec, developed by Josh Coalson in 2001 as a Xiph.org Foundation project) preserves every audio sample with mathematically exact precision: a decoded FLAC file produces bit-for-bit identical PCM to the original source. AAC discards auditory information by applying psychoacoustic models that predict which frequencies and transients are least perceptible to the human ear. At 256 kbps, the loss is virtually inaudible to the vast majority of listeners; at 128 kbps, some trained listeners may detect differences in direct comparisons with the source.
Spotify primarily uses the Ogg Vorbis codec for distribution on most platforms (Normal to Very High qualities: 96, 160, 320 kbps Vorbis). However, on iOS devices Spotify uses AAC because iPhones have hardware AAC decoding (the iPhone's audio chip has no Vorbis decoder in silicon). In practice, listeners on iPhone receive AAC streams. Apple Music uses exclusively AAC at 256 kbps. Tidal offers uncompressed FLAC under its HiFi Plus plan. So if your goal is to distribute in the Apple ecosystem or on Spotify iOS, AAC is the most efficient codec.
Convert FLAC to AAC: the optimal encoding chain for streaming
FLAC (Free Lossless Audio Codec) was developed by Josh Coalson and released as a Xiph.org Foundation project in July 2001. Unlike lossy codecs such as MP3 or AAC, FLAC preserves every audio sample with bit-for-bit accuracy: decoding a FLAC file produces exactly the same PCM as the original source, verifiable through hash comparison. The codec uses adaptive linear prediction (similar to LPC) followed by Golomb-Rice coding to compress the prediction residual. Typical compression ratio is 50–60% of the original WAV size, meaning a 700 MB CD becomes approximately 300–400 MB of FLAC with identical quality. FLAC is the preferred format for high-quality music archiving, studio master distribution, and high-fidelity collection storage. Platforms like Bandcamp allow direct FLAC downloads, and Tidal offers FLAC streaming through its HiFi Plus plan.
AAC (Advanced Audio Coding) was standardized by ISO/IEC in 1997 as part of MPEG-2 (MPEG-2 NBC, ISO/IEC 13818-7) and later incorporated into MPEG-4 Audio (ISO/IEC 14496-3). It was developed as the technical successor to MP3 by a consortium including Fraunhofer IIS, AT&T Bell Labs, Sony, Dolby, Nokia, and others. AAC-LC (Low Complexity) is the most widely implemented profile: it uses 2048-point transform windows (MDCT), temporal waveform prediction (TNS, Temporal Noise Shaping), Huffman coding of spectral coefficients, and a more sophisticated psychoacoustic modeling stage than MP3. Apple adopted AAC as the standard iTunes codec in 2003, and since then all its devices implement hardware AAC decoding (the iPhone's audio chip has had a silicon AAC decoder since the original iPhone in 2007). At 256 kbps AAC-LC, the format is widely considered transparent: blind listening studies such as those conducted by Hydrogenaudio demonstrate that most listeners cannot distinguish 256 kbps AAC from uncompressed source audio.
The fundamental technical reason to convert from FLAC (rather than from MP3 or another lossy format) is the quality of the source the AAC encoder receives. Modern AAC encoders (Apple Core Audio AAC, Fraunhofer FDK AAC, Nero AAC) use psychoacoustic models that analyze the complete audio spectrum to decide what information is inaudible and can be discarded. When the source is FLAC, these models work with complete, undegraded audio. When the source is MP3, the models receive audio that already bears MP3 encoding artifacts: frequencies above 16–20 kHz truncated, pre-echo artifacts on percussive transients, spectral smearing on high-energy frames. The AAC encoder cannot distinguish these artifacts from original audio and treats them as information to preserve — sometimes protecting MP3 artifacts while discarding real musical information. Convertir.ai performs the complete FLAC→AAC conversion in the browser: FLAC is decoded to PCM using libFLAC compiled with WebAssembly, and the PCM is encoded to AAC without transmitting audio to any external server.