Convert M4A to FLAC on iPhone
Converting a lossy M4A to lossless FLAC does not improve it. You get a much larger file containing exactly the same audio. There are real reasons to do it anyway — quality is not one of them.
This conversion cannot improve your audio. M4A normally contains AAC, which is lossy: the encoder permanently deleted parts of the recording. FLAC is lossless, which means it preserves whatever you give it — perfectly. Give it damaged audio and it perfectly preserves the damage, in a file two to five times larger. There is no app, on any platform, that recovers what a lossy encoder removed.
Why people expect otherwise
The word "lossless" does a lot of damage here. It sounds like a quality grade — as if moving a file into a lossless format upgrades it. It is not a grade. It is a promise about the conversion: FLAC guarantees that what comes out is bit-for-bit what went in.
So the promise holds perfectly. What went in was a decoded AAC stream — audio with holes already punched in it by the AAC encoder. FLAC faithfully, losslessly, permanently preserves those holes. The output is not better than the M4A. It is not even different from the M4A, audibly. It is just bigger.
This is the single most common misconception in audio conversion, and a great many converter apps are perfectly happy to let you keep believing it, because the conversion technically succeeds and you go away satisfied.
The cases where it is genuinely the right thing to do
They exist, and they are all about compatibility and workflow, never fidelity:
- A tool or device that only reads FLAC. Some music servers, DAPs, hi-fi streamers and library managers will ingest FLAC and refuse M4A. If the box only speaks FLAC, speak FLAC.
- An archive or catalogue standard that mandates it. Plenty of institutional and label pipelines specify FLAC for every asset regardless of provenance. That is a policy, and policies are not negotiable by argument.
- A processing chain that must not re-encode. If a file is going to be cut, tagged, re-tagged and passed through several tools, moving it to FLAC once means the remaining steps do not add a fresh generation of lossy damage each time. You are not repairing the file; you are stopping it getting worse.
- You want to stop the bleeding. If your only copy is the M4A and you are about to edit it, converting to FLAC (or WAV) first and editing that is sound practice — every subsequent save is lossless.
What Convexy actually writes
Convexy decodes the AAC inside your M4A to raw PCM, then encodes that PCM to FLAC on your device. The FLAC is written at 16-bit, or 24-bit if the source carries more than 16 bits of depth. You can preserve the source sample rate or force 44.1 kHz or 48 kHz, and preserve, downmix to mono, or keep stereo channels.
Expect the FLAC to be considerably larger than the M4A — commonly 2× to 5×. FLAC's compression is real but modest, because it is compressing audio that has already been through a codec designed to make it small.
If your .m4a happens to contain ALAC (Apple Lossless) rather than AAC — same extension, different codec — then everything above changes. ALAC is lossless, so ALAC to FLAC is a genuine lossless-to-lossless conversion with no quality cost at all. M4As from Voice Memos, iTunes purchases and video soundtracks are AAC; ALAC generally comes from a deliberate lossless rip.
What to do instead, if quality is the goal
Find the original. If the M4A was made from a CD, a WAV, an AIFF or a session file, go back to that and encode from there. A FLAC made from the true master is a real master. A FLAC made from an M4A is an expensive photocopy.
If the M4A is the original and always was — a Voice Memo, a purchased track — then accept it. Keep the M4A, and convert only when a specific device or workflow forces your hand.
How to do it
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Bring the M4A into Convexy
Tap Browse files and pick it from Files or iCloud Drive, or share it into Convexy from another app.
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Choose FLAC
Convexy lists only the formats your file can actually become. FLAC will be there alongside MP3, WAV, AIFF and CAF.
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Set sample rate and channels if you need to
Preserve is the right default. Only change them if the destination device or pipeline specifies otherwise.
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Convert
Decoding and re-encoding happen on your iPhone. Nothing is uploaded — there is no server to upload to.
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Save or share it
Save the FLAC to Files, or send it to the device or service that demanded FLAC in the first place.
Common questions
Will converting M4A to FLAC improve the sound quality?
No. It cannot. The AAC encoder that made your M4A permanently discarded audio data. FLAC losslessly preserves whatever it is given, so it preserves the file exactly as it now is — holes included. The result sounds identical to the M4A and takes up several times the space. No converter on any platform can reverse lossy compression.
Then why does Convexy offer M4A to FLAC at all?
Because there are legitimate reasons that have nothing to do with quality: hardware and software that only accept FLAC, archival policies that mandate it, and editing workflows where you want every step after this one to be lossless. The conversion is useful. It is just not an upgrade, and we would rather say so than let you find out later.
How much bigger will the FLAC be?
Typically two to five times the M4A. FLAC compresses, but it is compressing audio that AAC already squeezed hard, so there is much less redundancy left to exploit. A 5 MB M4A landing around 15–25 MB as FLAC is entirely normal.
Is FLAC better than M4A?
As formats, yes — FLAC is lossless and AAC is not. As files, a FLAC made from an M4A is not better than that M4A, because the quality ceiling was set the moment the AAC encoder ran. Format quality and file quality are different things, and conflating them is how people end up with 40 GB of lossless files that sound exactly like the 8 GB they started with.
What if my M4A is Apple Lossless (ALAC)?
Then this is a genuinely lossless conversion. ALAC and FLAC are both lossless codecs, so converting between them preserves the audio exactly — you are only changing the wrapper, usually because FLAC has broader support outside Apple's world. Most .m4a files are AAC, not ALAC; ALAC usually comes from a deliberate lossless rip.
Does the conversion happen on my phone?
Yes, entirely. There is no upload and no account. It works in Airplane Mode, which is the simplest way to prove it to yourself.