How to convert mp3 to flac — free, browser-based, no upload
- Step 1Open the converter — Go to the MP3 to FLAC tool. The first run downloads the FFmpeg 8.1 WebAssembly engine (cached afterward), so the first conversion in a session is slightly slower to start.
- Step 2Drop your MP3 — Drag one
.mp3onto the dropzone or click to browse. There's no account prompt and nothing uploads. Free-tier files can be up to 50 MB and 30 minutes long. - Step 3Leave compression at 8, or change it — The Compression level menu defaults to
8 - default sweet spot. Pick0 - fastestif you just want speed, or12 - smallest, slowestto minimise size. None of these change the audio. - Step 4Convert — The browser decodes the MP3 and encodes FLAC locally. A typical song takes a few seconds; there's no upload step, so the only time spent is CPU encode time.
- Step 5Download the FLAC — Click download to save the
.flac. No temporary cloud link, no expiry — the file is generated on your machine and saved directly. - Step 6Convert the next one — Drop another file to repeat. The engine stays cached for the session, so subsequent conversions start instantly.
In-browser vs. typical upload-based converters
Why running FFmpeg locally differs from the usual cloud MP3-to-FLAC sites.
| Aspect | This tool (in-browser) | Typical upload site |
|---|---|---|
| Where audio is processed | Your CPU, in the tab | Their server |
| Upload required | No | Yes (whole file) |
| Account / sign-up | No | Often required |
| Watermark on output | No | Sometimes |
| Daily conversion cap | No (tool itself) | Common on free plans |
| Privacy of audio | Never leaves device | Held on server temporarily |
| Engine | FFmpeg 8.1 (WASM) | Server-side (varies) |
The single control: FLAC compression level
Exactly the four options shown in the UI. The level changes size and encode time only — the FLAC always decodes to the same PCM.
| Value | UI label | Speed | Size |
|---|---|---|---|
| 0 | 0 - fastest | Fastest | Largest |
| 5 | 5 - balanced | Fast | Mid |
| 8 | 8 - default sweet spot | Moderate | Small |
| 12 | 12 - smallest, slowest | Slowest | Smallest |
Audio tier limits (per file)
What the free tier allows and where upgrading helps. Duration is a separate cap from file size.
| Tier | Max size | Max duration | Files/batch |
|---|---|---|---|
| Free | 50 MB | 30 min | 1 |
| Pro | 200 MB | 120 min | 10 |
| Pro-media | 100 GB | Unlimited | 100 |
| Developer | 100 GB | Unlimited | Unlimited |
Cookbook
Quick, real conversions for the no-fuss case — drop a file, get a FLAC. The audio is always identical to the source MP3.
The two-click default conversion
The fastest path: drop the file, accept the default level 8, download. No settings to think about.
1. Drop song.mp3 (4.0 MB, 192 kbps, 3:30) 2. Compression level stays at 8 (default) 3. Download song.flac (~5.2 MB) No upload, no account, no watermark. Audio in the FLAC decodes identical to the MP3.
Choosing speed on a slower laptop
On an older machine, level 0 finishes faster at the cost of a bigger file. Useful when you just need the FLAC quickly.
Drop: voice-memo.mp3 (8 MB, 22:00) Level: 0 - fastest -> voice-memo.flac produced in the shortest time. File is larger than level 8 would give, but identical audio. Re-encode at 8 or 12 later if size matters.
Confirming nothing uploaded
You can verify the privacy claim yourself with the browser's network panel.
Open DevTools -> Network tab -> convert a file. You'll see the FFmpeg .wasm download (once, then cached). You will NOT see your MP3 being POSTed anywhere. Disconnect from Wi-Fi after the engine loads and the conversion still works -- proof it's all local.
Free-tier size check
Free allows 50 MB and 30 minutes per file. A long DJ mix can exceed those even at modest bitrate.
mixtape.mp3 128 kbps, 55:00, 52 MB Free tier: rejected -- over 50 MB AND over 30 min. Options: trim with the audio trimmer, or upgrade to Pro (200 MB / 120 min).
Quick FLAC, then back to MP3 for a device
If you converted to FLAC but your player only takes MP3, the reverse tool turns it back with a bitrate choice.
song.mp3 --(this tool)--> song.flac song.flac --(flac-to-mp3)--> song.mp3 (pick bitrate) Use the [FLAC to MP3 converter](/audio-tools/flac-to-mp3). Heads up: that final step is a fresh lossy encode.
Edge cases and what actually happens
Expecting better sound after conversion
By designFree or paid, no MP3-to-FLAC converter can add back data the MP3 codec discarded. This tool gives you a lossless FLAC of the existing audio — same sound, different container. If a site promises 'enhanced' or 'restored' quality from MP3, that claim is false.
First conversion in a session feels slow to start
ExpectedThe FFmpeg 8.1 WebAssembly engine (a few MB) downloads on first use, then caches. The initial conversion includes that one-time load; every conversion after it in the same session starts immediately. This is the only network activity — your MP3 itself never uploads.
File over the free 50 MB / 30 min limit
RejectedFree tier caps each file at 50 MB and 30 minutes, and these are independent — a long low-bitrate file can pass the size check but fail on duration. Trim it with the audio trimmer or move to Pro (200 MB / 120 min).
Trying to drop multiple files at once
Single fileMP3 to FLAC processes one file at a time. Convert them one after another in the same session; the engine stays loaded so it's quick. There's no hidden batch upload happening behind the scenes.
Output FLAC larger than the source MP3
ExpectedThis surprises people expecting 'lossless = smaller'. FLAC is smaller than uncompressed WAV, but larger than a lossy MP3, because decoded MP3 audio compresses poorly. A 4 MB MP3 commonly becomes a 5-6 MB FLAC. That's normal and not a sign of added quality.
Private browsing / cleared cache re-downloads the engine
ExpectedIncognito or a cleared cache means the WASM engine downloads again on next use. Conversions still work and stay local; you just pay the one-time load again. Audio is never uploaded regardless of cache state.
Mislabeled file (e.g. an AAC renamed to .mp3)
MismatchThe tool reads the extension from the filename to set up the pipeline, but FFmpeg decodes by actual content. A file renamed to .mp3 that's really another codec may still decode, though it's not the intended path. For M4A/AAC sources, use M4A to MP3 first or the matching converter.
Dropping a FLAC or WAV by mistake
MismatchThis page is for MP3 input to FLAC output. For WAV sources use WAV to FLAC; to go the other way (FLAC to MP3) use FLAC to MP3. Picking the right tool avoids a pointless round-trip.
Tab closed during a long encode
Re-run requiredThere's no server job to resume — everything is in the tab. If you close or refresh mid-encode on a long file, just re-open the tool and run it again. The original MP3 on disk is untouched.
Browser without WebAssembly / very old device
UnsupportedFFmpeg-WASM needs a modern browser with WebAssembly support. Current Chrome, Edge, Firefox and Safari all qualify. A very old browser may fail to load the engine; updating the browser resolves it.
Frequently asked questions
Is this MP3 to FLAC converter really free?
Yes. There's no account, no sign-up wall, and no watermark on the output. The tool runs FFmpeg in your browser, so there are no server costs per conversion to recoup with a paywall. Higher tiers exist only to raise per-file size/duration limits and batch counts.
Do I have to upload my MP3?
No. The file is read into your browser's memory and processed on your own CPU by FFmpeg 8.1 (WebAssembly). It never leaves your device. You can confirm it in DevTools' Network tab — only the engine downloads, never your audio.
Do I need to create an account?
No account is required to convert. Just open the tool, drop an MP3, and download the FLAC. Optional sign-in is only relevant if you want a higher tier's larger limits.
Will it add a watermark or alter my audio?
No watermark, and no audible change. The output FLAC decodes to exactly the same audio as the source MP3 — it's a lossless re-container. The only choice you make (compression level) affects file size and encode speed, not sound.
Why does the first conversion take a moment to start?
The FFmpeg WebAssembly engine downloads once on first use, then caches. The first conversion in a session includes that load; the rest are instant. Your MP3 is never part of that download — only the engine is.
Does it work offline?
After the engine has loaded once in a session, yes — you can disconnect and conversions still run, because all processing is local. The only thing that needs the network is the initial engine download (and re-download if your cache is cleared).
What's the biggest file I can convert for free?
On the free tier, up to 50 MB and 30 minutes per file, one at a time. Pro raises that to 200 MB / 120 min and 10 files per batch; Pro-media and Developer go to 100 GB with unlimited duration.
Why is the FLAC bigger than my MP3?
Because MP3 is lossy and small by discarding data, while FLAC stores the decoded audio losslessly. Lossless of an already-lossy source is bigger than the lossy original. Expect roughly 20-40% larger. Level 12 trims a little but won't beat the MP3's size.
Which browsers are supported?
Any modern desktop browser with WebAssembly — current Chrome, Edge, Firefox, and Safari on Windows, macOS, Linux, or ChromeOS. No extension or install is needed.
Can I convert several MP3s in one go?
This tool is one file at a time. Run them in sequence in the same session; the engine stays cached so each subsequent conversion starts immediately. There's no bulk upload involved.
Are my tags and cover art kept?
Yes when present. ID3 tags map into FLAC Vorbis comments and an embedded cover image is re-attached. To edit fields afterward, use the ID3 / tag editor; to pull a cover from another file, use the album-art extractor.
I converted to FLAC but my device only plays MP3 — now what?
Use the FLAC to MP3 converter to go back, choosing a bitrate. Just remember that step is a fresh lossy encode, so if you still have the original MP3, use that for the device instead of re-encoding the FLAC.
Privacy first
Every JAD Audio tool runs entirely in your browser via FFmpeg (WebAssembly) and RNNoise. Your audio files never leave your device — verified by zero outbound network requests during processing.