Convert FLAC to MP3
Take a lossless library somewhere that will not play it.
How it works
FLAC compresses without discarding. It predicts each sample from the ones before it using a short linear model, stores only the prediction error, and codes those errors with Rice coding, which spends few bits on the small numbers that dominate ordinary music. Decoding reverses the arithmetic exactly, so a decoded FLAC is bit-for-bit the file that went in.
The payoff is around 50 to 60 percent of the WAV, depending on the material: dense, loud mastering compresses least, solo piano and quiet acoustic recordings most. That still leaves an album at 250 to 400 MB, which is why this page exists.
Where FLAC stops being convenient
Support is good and not universal. Every desktop player and every Android phone reads FLAC; so do most network streamers and a growing number of car systems. Apple never adopted it, so an iPhone will not import a FLAC into its music library without a third-party app, and the great majority of car head units, Bluetooth speakers with SD card slots, older iPods and portable players stop at MP3.
There is also a bandwidth argument that has nothing to do with playback. Sending an album to someone over a messaging app, attaching a recording to an email, or fitting a collection onto a phone with 64 GB of storage are all size problems, and lossless is the wrong tool for a size problem.
This transcode is the good kind
Unlike converting between two lossy formats, this one starts from the original signal. The MP3 encoder receives exactly what the recording contained and makes a single set of decisions about what to discard, which is the same situation as encoding from the master. There is no compounding, and no reason to pad the bitrate defensively.
That makes 192 kbps a genuinely good result and 320 kbps close to the limit of what the format can express. Choosing 320 costs about 2.4 MB per minute against 1.4 MB at 192, which on a phone with room to spare is a reasonable way to stop thinking about it.
Tags come across: title, artist, album, track number, date and genre all have direct equivalents in ID3. Embedded cover art, ReplayGain values, cue sheets for a single-file album rip and any unusual Vorbis comment fields do not survive, so a rip stored as one FLAC per disc with a cue sheet is better split before conversion than after.
Questions
Will I hear the difference?
At 320 kbps, in a car or on earbuds, almost certainly not. On good headphones in a quiet room, some people reliably identify 320 kbps MP3 against lossless on particular recordings, usually ones with cymbals, applause or harpsichord where the encoder's model has least masking to exploit. On most material and most equipment the difference is below the noise floor of the listening environment.
Is my music uploaded?
No. FLAC is decoded by the browser and re-encoded by a WebAssembly build of LAME in a Web Worker, both on your machine. The Network tab stays quiet after the page and the encoder module have loaded. For a library of any size that also makes this far faster than any service that has to receive the files first.
What about 24-bit or 96 kHz FLAC?
It converts, and what makes it high resolution does not carry over. MP3 has no concept of bit depth beyond what its own representation implies, and the format defines no sample rate above 48 kHz, so a 96 kHz source is resampled on the way through. The result is a correct MP3 of the same performance. Keep the FLAC as the archive copy.
Can I convert a whole album at once?
One file at a time on this page. There is no daily limit and no queue, so a twelve-track album is twelve drops, each taking a second or two, and nothing is counted against you. Keeping it to one file per run also keeps memory predictable on a phone, where a batch of lossless tracks would be the thing that breaks first.