Convert FLAC to MP3 on iPhone
FLAC is a lossless master. MP3 is what plays everywhere. Convert one to the other on the phone, keep the original, and stop pretending you have to choose.
FLAC is lossless — which makes this a clean encode
FLAC (Free Lossless Audio Codec) is compressed, but not lossy. It works the way ZIP does: it finds redundancy in the data and packs it away, and when you decode it you get back the exact same samples, bit for bit. A FLAC is typically 50–60% the size of the equivalent WAV and is byte-for-byte identical in what it decodes to.
That matters here, because it means your FLAC is a genuine master. Encoding an MP3 from it is a first-generation encode: the MP3 encoder gets the real audio, not a lossy approximation of it, and makes its own decisions once. This is the correct way to produce an MP3.
Compare that to transcoding an M4A or an existing MP3, where a second encoder piles new damage on top of old. Different situation entirely — and the reason serious music libraries are archived in FLAC and exported to MP3 rather than the reverse.
Why you would want the MP3 at all
FLAC's problem has never been quality. It is that a lot of hardware simply will not play it:
- Car head units. A great many read MP3 off a USB stick and nothing else.
- The Apple ecosystem. iOS can play a FLAC sitting in the Files app, but the Music app library does not accept FLAC. If you want it in your library, it needs to be something else.
- Older DAPs, gym equipment, in-flight systems, cheap Bluetooth receivers.
- Storage. A 500-track FLAC library is not going on a phone. The same library at 256 kbps MP3 will.
The right pattern is boring and correct: archive in FLAC, carry MP3s. You lose nothing, because the master is still sitting where you left it.
One reason MP3 output is scarce on iPhone: Apple's audio frameworks cannot produce an MP3 at all. They decode it; they have never encoded it. An app that offers MP3 output either brings its own encoder or ships your file off to a machine that has one. Convexy brings its own — the LAME encoder, compiled into the app — so a 40-minute FLAC never leaves the phone.
Size, honestly
A FLAC's size depends on the music. Dense, loud material compresses badly; sparse, quiet material compresses well. Typically a CD-quality FLAC lands around 25–35 MB for a 5-minute track.
The MP3's size, by contrast, depends only on bitrate and duration:
- 320 kbps — about 2.4 MB per minute (a 5-minute track ≈ 12 MB).
- 256 kbps — about 1.9 MB per minute. Convexy's default.
- 192 kbps — about 1.4 MB per minute.
- 128 kbps — about 1 MB per minute. Do not use this for music you care about.
For a lossless source going to a car stereo or a phone, 320 kbps is the honest answer. The storage you save at 192 kbps is not worth the argument you will have with yourself later.
High-resolution FLAC
If your FLAC is 24-bit / 96 kHz, understand what MP3 can and cannot carry. MP3 is a 16-bit-equivalent lossy format and tops out at 48 kHz. The extra bit depth and sample rate will not survive — not because Convexy discards them, but because the MP3 format has nowhere to put them.
That is fine. It is what the format is for. Set the sample rate to 44.1 kHz or 48 kHz deliberately rather than letting a resampler make the decision for you, encode at 320 kbps, and keep the hi-res FLAC as the master it was always meant to be.
How to do it
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Bring the FLAC into Convexy
Tap Browse files and pick it from Files or iCloud Drive, or share it into Convexy from wherever it lives.
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Choose MP3
Convexy shows only what a FLAC can actually become — MP3, M4A, WAV, AIFF or CAF.
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Set the bitrate
320 kbps for music. Leave sample rate on Preserve unless the FLAC is high-resolution, in which case pick 44.1 kHz or 48 kHz.
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Convert
The bundled LAME encoder runs on your iPhone. No upload, no account, works offline.
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Save or share it
Save the MP3 to Files, or send it straight to the app or drive it needs to reach. The FLAC is untouched.
Common questions
Does FLAC to MP3 lose quality?
Yes. MP3 is lossy and permanently discards audio; FLAC does not. But because FLAC is a lossless source, this is a single, first-generation encode — the best MP3 that recording can produce. At 320 kbps the difference is genuinely hard to hear on normal equipment. Keep the FLAC and the loss costs you nothing you cannot get back.
Can I convert MP3 back to FLAC and get the quality back?
No. This is the single most common misunderstanding in audio conversion. Wrapping a lossy file in a lossless format produces a bigger file containing exactly the same damaged audio. FLAC preserves whatever you give it perfectly — including everything the MP3 encoder already threw away. There is no recovery, ever.
Why can't my iPhone play FLAC in the Music app?
iOS can decode FLAC — a FLAC in the Files app will play. What it will not do is accept FLAC into the Music app library. That is a library restriction, not a codec one. Converting to MP3 (or M4A) is the practical way in.
Is 320 kbps MP3 as good as FLAC?
Not literally — FLAC is bit-exact and MP3 is an approximation, and no amount of bitrate closes that gap in principle. In practice, on a phone, in a car, at the gym, a 320 kbps MP3 from a clean lossless source is not the weak link in your listening chain. Archive the FLAC; carry the MP3.
How does an iPhone app encode MP3 at all?
By bringing its own encoder. iOS has never included one — the MP3 encode format is absent from the system's list of available encoders, so Apple's frameworks cannot produce an MP3 at any setting. MP3's patents all expired in April 2017, so this costs nobody anything; Apple simply never added it. Convexy compiles in LAME, the standard open-source encoder, and runs it locally.