Skip to converter

MP3 to FLAC converter

The policy and the material disagree: an archive that demands lossless files, holding material that only exists as MP3. FLAC gives byte-level integrity for the samples that survive the decode; it cannot undo what the MP3 encoder discarded decades ago.

FLAC stores lossless PCM, but the source is already decoded: any lossy source keeps its existing loss.

Drop files here or MP3, up to 60 MB
    Add a file to start.

    Processed on your device. Files aren’t sent anywhere.

    No sign-up. Nothing to install.

    Write the decision before running the batch

    Illustrative: a station archive holds 1990s interviews as MP3, and the new policy requires lossless files. Re-recording is impossible, so the migration has to be honest about what it preserves. The decision is not 'make the audio good'; it is 'make the bytes stable'.

    OptionWhat the shelf gainsWhat it costs
    Keep MP3 onlyNothing changesPolicy unmet; no stable lossless shelf
    MP3 to FLACLossless storage of surviving samples, stable checksumsShelf grows; lossy history must be documented
    MP3 to WAVRaw PCM, simple toolingShelf grows several times larger than FLAC
    Re-recordFull fidelityImpossible for archived material

    The policy conflict, stated plainly

    Does FLAC make the MP3 lossless?
    FLAC is lossless relative to whatever it stores. Converting an MP3 stores the decoded samples exactly, so the shelf is lossless from here on — but audio information the MP3 discarded at encode time is still absent.
    Why FLAC instead of keeping MP3?
    A shelf needs stable bytes. FLAC stores the samples without further loss and gives you checksums that stay valid across migrations; MP3 files are fine to play but awkward as an archive of record.
    Why not convert to WAV instead?
    WAV also stores raw PCM, but the shelf grows several times larger. FLAC stores the same samples smaller, which is why it suits a shelf of hundreds of files.
    Should the original MP3 be deleted?
    No. Keep the MP3 as the provenance artefact. The FLAC copy describes what the MP3 contained, and the note beside it should say that the source was lossy.
    Is the archive uploaded?
    No. Decoding and encoding run inside this page through a self-hosted FFmpeg worker; the first run loads the WASM core from this site over http or https.

    Running the shelf, one file at a time

    One file per run, up to 60 MiB and 600 seconds of audio. A shelf of hundreds of files is a repeated run with discipline, not a bulk operation.

    1. Drag the MP3 onto this page; the local FFmpeg worker loads on first use
    2. Convert, then read the reported codec, duration, sample rate and channel count
    3. Name the FLAC file after the catalogue number, not the MP3's filename
    4. Write the provenance note beside it: source format, source bitrate if known, migration date

    Integrity checks that survive a migration

    A shelf is only trustworthy if it can be verified after a move. Checksums over the FLAC files give that; duration comparison catches a decode that came out short.

    • The engine probes the encoded file and compares codec and duration with the source; drift beyond a small tolerance is reported as failure
    • Keep a checksum list beside the shelf and re-run it after any storage move
    • Read the reported sample rate rather than assuming it — encoder builds differ in the rates they accept
    • Never re-encode the FLAC copy back to MP3 as a 'cleanup'; that adds loss

    What the provenance note has to say

    One line per file: source: MP3, 128 kbps; migrated to FLAC; lossy source, detail not restored. Without it, a future reader assumes the shelf holds native recordings, and that assumption is wrong.

    Where FLAC on the shelf pays off

    The shelf is the input for everything else: delivery copies, transcription runs, measurement passes. Encoding from FLAC means each downstream job starts from stable bytes instead of from a lossy file that gets re-encoded again.

    • Delivery copies: encode from the shelf with FLAC to MP3 or FLAC to Ogg
    • Editing and measurement: decode from the shelf with FLAC to WAV
    • Future migrations: the shelf is the source of record, not the old MP3 folder

    Share this converter

    More sharing options