Compressed audio that loses nothing — and, on iPhone, a format Filemorph can read and edit but can't create.
FLAC (Free Lossless Audio Codec) compresses audio the way a ZIP file compresses a document — shrinking the file size while preserving every bit of the original data, so decompressing a FLAC file reproduces the source recording exactly rather than an approximation. That puts it roughly halfway between WAV and MP3: smaller than fully uncompressed audio, but with none of the quality tradeoff that comes with MP3 or AAC's lossy compression. Audiophiles, archivists, and musicians distributing high-resolution recordings favor FLAC for exactly that reason, and it has become the de facto standard for lossless music downloads and archival copies outside of Apple's own ecosystem. The one place FLAC runs into trouble on iPhone is creation: Apple's on-device audio-export framework can decode and play FLAC without any issue, but it cannot encode new FLAC files, so an app built entirely on that framework — Filemorph included — can trim, merge, or transcribe a FLAC file, yet has no way to produce a new one as output.
iPhone and Mac play FLAC natively in the Music and Files apps as of recent iOS and macOS versions, though older versions required a third-party player. Most Android phones and a wide range of dedicated music players support FLAC well. Windows Media Player and some car stereos still do not play it without an added codec.
FLAC's lossless quality matters for archiving and critical listening, but it plays natively in far fewer apps than M4A or MP3, and it cannot be created fresh on iPhone at all. Converting an existing FLAC file to M4A on-device makes it playable everywhere Apple's ecosystem expects audio, at a size closer to what messaging and storage actually need.
Filemorph can convert FLAC to M4A on-device — the format that plays everywhere in Apple's ecosystem, since Filemorph cannot encode a new FLAC file on iPhone.
Filemorph converts .flac files entirely on-device on iPhone, iPad and Mac — no upload, no account, and it works in Airplane Mode.
Relevant operations in Filemorph:
No. Filemorph can open, trim, merge, and transcribe FLAC files, but it cannot encode new ones — Apple's on-device audio framework supports decoding FLAC but not writing it, a limitation shared by most iPhone apps built on that framework.
Both are lossless, but WAV is uncompressed while FLAC compresses the same audio data without discarding anything, typically to around half the file size. Decompressing a FLAC file reconstructs the exact original samples, the same guarantee WAV provides without the compression step.
No. Filemorph decodes and converts FLAC files entirely on-device — a high-resolution album or recording never leaves the iPhone or iPad, and the process works the same with no internet connection.