What Is FLAC?
FLAC stands for Free Lossless Audio Codec. It is an audio compression format that reduces file sizes without discarding any audio data whatsoever. When you decode a FLAC file, the output is a bit-for-bit identical reconstruction of the original uncompressed audio. Not approximately identical, not perceptually identical, but mathematically identical down to every single sample.
Developed by Josh Coalson and released as an open-source project in 2001, FLAC has become the dominant lossless audio format for consumer use. It is maintained by the Xiph.Org Foundation, the same organization behind the OGG Vorbis and Opus codecs. Being open source and royalty-free means anyone can use, distribute, and implement FLAC without paying licensing fees, which has encouraged widespread adoption across devices, software, and streaming services.
FLAC files use the .flac extension and carry the MIME type audio/flac. The format supports bit depths from 4 to 32 bits per sample, sample rates from 1 Hz to 655,350 Hz, and up to 8 audio channels. In practice, most FLAC files contain standard CD-quality audio at 16-bit, 44.1 kHz stereo, or high-resolution audio at 24-bit with sample rates of 48 kHz, 96 kHz, or 192 kHz.
The key value proposition of FLAC is simple: it gives you perfect audio fidelity in a file that is substantially smaller than raw uncompressed audio. Think of it as the audio equivalent of a ZIP file. You compress it to save space, and when you decompress it, you get back exactly what you put in.
How Lossless Compression Works
To understand FLAC, it helps to understand the fundamental difference between lossy and lossless compression and the specific techniques FLAC uses.
Lossy compression, used by formats like MP3 and AAC, achieves small file sizes by permanently removing audio data that psychoacoustic models predict the listener will not miss. The discarded data is gone forever. Decoding a lossy file produces audio that is close to the original but not identical.
Lossless compression achieves size reduction by finding and exploiting patterns and redundancies in the data without discarding anything. The process is fully reversible. FLAC uses a multi-stage pipeline to accomplish this.
First, FLAC divides the audio into blocks, typically 4,096 samples long. For each block, the encoder applies linear prediction, which models each sample as a mathematical function of the preceding samples. Because audio signals are highly correlated from one sample to the next (a waveform is smooth, not random noise), the prediction is usually quite close to the actual value. The encoder then stores only the small difference between the predicted and actual values, called the residual.
These residuals are much smaller numbers than the original sample values, so they can be represented with fewer bits. FLAC then applies Rice coding, a form of entropy coding, to these residuals. Rice coding assigns shorter binary codes to smaller and more common values and longer codes to larger and rarer values, further reducing the total number of bits needed.
The result is a compressed stream that is typically 50 to 70 percent of the original file size. The exact compression ratio depends on the audio content. Simple signals like solo instruments and spoken word compress more efficiently. Complex signals like dense orchestral music or heavily distorted rock compress less. Complete silence compresses to nearly nothing.
Crucially, every step of this process is mathematically reversible. The decoder can reconstruct the exact original samples from the stored residuals and prediction coefficients. No approximation is involved. No audio data is lost.
FLAC vs Other Lossless Formats
FLAC is not the only lossless audio format available. Several alternatives exist, each with distinct characteristics.
Apple Lossless Audio Codec (ALAC) is Apple's lossless format, developed in 2004 and open-sourced in 2011. ALAC achieves compression ratios nearly identical to FLAC and is natively supported on all Apple devices. The primary reason to choose ALAC over FLAC is deep integration with the Apple ecosystem, including iTunes, Apple Music, and the native Music app. However, FLAC has broader support outside the Apple world, and since Apple added FLAC playback support in iOS 11 and macOS High Sierra, the advantage of ALAC has diminished. Apple Music's lossless tier uses ALAC for delivery.
Windows Media Audio Lossless (WMA Lossless) is Microsoft's lossless codec. It delivers comparable compression ratios to FLAC but is largely confined to the Windows ecosystem. Support on non-Microsoft platforms is limited, and the format has never gained significant traction among audiophiles or in the broader market.
WavPack is an open-source format that offers a unique hybrid mode. It can create a lossy base file plus a correction file that together reconstruct the original losslessly. This allows you to carry the smaller lossy file on portable devices while keeping the correction file at home for archival purposes. WavPack is technically impressive but has limited device and software support compared to FLAC.
Monkey's Audio (APE) achieves slightly better compression ratios than FLAC but requires significantly more processing power to decode. This makes it impractical for mobile devices and embedded hardware. Its device support is also much more limited than FLAC's.
In practice, FLAC has won the lossless format war for most purposes. Its combination of open-source licensing, excellent compression, fast decoding, broad device support, and robust metadata handling makes it the default choice for lossless audio distribution and archival. The only major exception is within the Apple ecosystem, where ALAC remains the native option.
FLAC File Sizes: What to Expect
Understanding FLAC file sizes helps you plan storage requirements and decide when lossless quality is worth the space tradeoff.
A standard CD-quality FLAC file (16-bit, 44.1 kHz stereo) typically runs 700 to 1,000 kilobytes per second of audio, or roughly 25 to 45 megabytes for an average four-minute song. The equivalent WAV file would be about 40 to 42 megabytes, so FLAC saves approximately 30 to 50 percent depending on the musical content.
High-resolution FLAC files are substantially larger. A 24-bit, 96 kHz recording occupies roughly two to three times the space of a CD-quality FLAC of the same duration. A 24-bit, 192 kHz recording is larger still. A single four-minute song at 24-bit/192 kHz might be 150 to 200 megabytes in FLAC.
For comparison, the same four-minute song as a 320 kbps MP3 would be about 9 to 10 megabytes, and at 128 kbps MP3 about 3.8 megabytes. FLAC files are roughly 3 to 5 times larger than high-quality lossy files and 8 to 12 times larger than moderate-quality lossy files.
A full CD album (approximately 60 minutes of audio) in CD-quality FLAC typically occupies 250 to 400 megabytes. A 1-terabyte hard drive can store roughly 2,500 to 4,000 CD-quality FLAC albums. A 256-gigabyte smartphone can hold 600 to 1,000 FLAC albums, though this is a significant portion of the device's total storage.
These sizes are meaningful but manageable with modern storage. The real question is not whether you can afford the space but whether the quality difference justifies it for your listening habits and equipment.
Device and Software Support for FLAC
FLAC support has expanded dramatically over the past decade, reaching a point where compatibility is rarely a concern for most users.
On desktop operating systems, Windows has supported FLAC natively since Windows 10. macOS added native FLAC playback in macOS High Sierra (10.13). Linux has supported FLAC since the format's inception, as it is part of the open-source audio ecosystem. Popular media players like VLC, foobar2000, Winamp, and Audacity support FLAC across all platforms.
On mobile devices, Android has included native FLAC support since Android 3.1 (Honeycomb). iOS added FLAC playback in iOS 11. This means virtually all smartphones sold in the past several years handle FLAC without any third-party apps. Music player apps like Poweramp, Neutron, and VOX offer enhanced FLAC playback with additional features like equalizers and gapless playback.
In the streaming world, several major services offer FLAC-quality audio. Tidal offers FLAC streaming in its HiFi tier. Amazon Music HD delivers lossless audio using FLAC. Apple Music uses ALAC for its lossless tier, which is functionally equivalent. Qobuz streams in FLAC at up to 24-bit/192 kHz.
Hardware support is broad and growing. Most modern car stereos with USB input support FLAC. Network audio streamers from brands like Sonos, Bluesound, Cambridge Audio, and Denon all support FLAC. Many Bluetooth speakers can receive and decode FLAC when connected via WiFi, though Bluetooth transmission itself typically involves lossy re-encoding unless using LDAC or similar high-bandwidth Bluetooth codecs.
The notable gap is in some budget consumer electronics and older hardware. Inexpensive portable speakers, older iPods, and legacy car stereos may not recognize FLAC files. For these cases, converting to MP3 or AAC before transferring the files is the practical solution.
When FLAC Actually Matters
The honest answer to whether FLAC sounds better than a high-bitrate lossy format depends on several factors, and it is not always yes in a way that matters.
FLAC objectively contains more audio data than any lossy format. A spectral analysis will reveal that FLAC preserves the full frequency spectrum while MP3 and AAC roll off high frequencies and introduce subtle quantization artifacts. This is measurable and indisputable.
Whether this difference is audible depends on three things: the quality of your playback equipment, the characteristics of the audio content, and your listening acuity.
Playback equipment matters enormously. Listening through budget earbuds, laptop speakers, or a typical Bluetooth speaker, even trained listeners struggle to distinguish 256 kbps AAC from FLAC in controlled blind tests. These transducers simply cannot reproduce the subtle details that differentiate the two. However, with high-quality headphones (particularly open-back models from manufacturers like Sennheiser, Beyerdynamic, or Audeze), a good headphone amplifier, and a capable DAC, the differences become more perceptible. The same applies to high-fidelity speaker systems in acoustically treated rooms.
Content matters too. Dense, complex music with wide frequency range, such as orchestral recordings, jazz ensembles, and acoustic performances, reveals compression artifacts more readily than simple pop productions, heavily compressed rock, or spoken word. If your library consists primarily of podcasts and electronic dance music, the benefit of FLAC over a high-bitrate lossy format is minimal.
Perhaps the most compelling reason to choose FLAC is not about what you hear today but about preserving options for the future. FLAC is an archival format. If you rip your CD collection to FLAC, you have a perfect digital copy from which you can create any lossy format at any bitrate whenever you need it, without generational loss. If you rip to MP3 and later want AAC, you are transcoding from one lossy format to another, compounding quality degradation. FLAC is a future-proof investment in your music library.
Converting FLAC Files
There are many reasons you might need to convert FLAC files to or from other formats. You might need to create MP3 copies for a device that does not support FLAC. You might want to convert a WAV recording to FLAC for more efficient archival storage. Or you might need to convert FLAC to AAC for Apple Music compatibility.
When converting from FLAC to a lossy format like MP3 or AAC, the process involves decoding the FLAC to raw PCM audio and then encoding that audio with the lossy codec. Since FLAC decoding perfectly reconstructs the original audio, this is equivalent to encoding directly from the uncompressed source. There is no quality penalty for starting from FLAC instead of WAV.
When converting from WAV to FLAC, the process is purely lossless. The FLAC encoder compresses the raw PCM data using predictive modeling and entropy coding. The resulting FLAC file will be 30 to 50 percent smaller while containing identical audio data. This conversion is essentially free in terms of quality and highly recommended for anyone storing uncompressed audio files.
When converting from a lossy format to FLAC, the resulting file will be larger than the source but will not sound any better. The audio data that was discarded during lossy encoding cannot be recovered. The FLAC file will faithfully preserve the lossy decode, but it is preserving an already degraded signal. This conversion is only useful if you need FLAC for compatibility reasons and have no access to the original lossless source.
ConvertFree handles all of these FLAC conversion scenarios directly in your browser. Whether you need to convert FLAC to MP3 for your portable player, WAV to FLAC for efficient archival, or FLAC to AAC for your iPhone, the conversion happens locally on your device with no file uploads, no accounts, and no privacy concerns. The browser-based processing ensures your music files never leave your computer.
For batch conversions of large FLAC libraries, process files sequentially through ConvertFree. Since there are no server-side limitations, you can convert as many files as you need at whatever quality settings you prefer.