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Opus to M4A Converter

Turn Opus files into M4A in a couple of clicks. Opus is the best low-bitrate codec available — voice and music; M4A is an MP4 container holding AAC or ALAC audio. Some detail is discarded to fit the target format; how much depends on the format and your settings.

Not uploaded to any serverConverted on this deviceGone when you close the tabHow this works

Drop your files here

Opus files (.opus) · up to 300 MB each

or paste files from your clipboard

Ready when you are

Drop a Opus file above and FileTools360 will turn it into M4A — right here on your device, without uploading anything.

⌘K to search converters

How to use it

1
Add your Opus files
Drag them onto the drop area, choose them from your device, or paste them from your clipboard. You can queue several at once. Nothing is sent anywhere — the file stays on this device.
2
Adjust the settings if you want to
The defaults suit most people. Open Advanced to control bitrate, sample rate and channels.
3
Convert and download
Press Convert. Everything happens on your own device — nothing is uploaded. Download files one by one, or grab them all as a ZIP.

Privacy, in plain words

Is it safe? Your Opus file is not uploaded anywhere

What “uploaded” normally means. On most online converters, pressing the button copies your file across the internet onto a computer owned by that website. That copy is what the word “upload” means, and it is the part nobody explains.

What happens instead. This site does not do it. There is no server here that receives files, so your Opus file is read, converted and handed back by the browser you are using right now. It never travels — so there is no copy to store, read, leak or hand over.

Check it yourself in ten seconds

Turn off your Wi-Fi after this page has loaded, then convert a file anyway. It still works, because everything needed is already on your device.

The longer explanation of how this works, and the full detail of what is and is not stored on the privacy page.

Why this matters more than it sounds

An audio file is a conversation. Transcribed by machine — which is cheap now — it becomes searchable text about whoever was speaking. It matters more than it sounds, because of what audio files usually are:

Therapy and consultation recordings

clinical material with strict handling rules

Meeting audio

internal discussion, named people, unannounced decisions

Unreleased music

work whose commercial value depends on control of the master

Call recordings

both sides of a conversation, often legally sensitive

A file that is never sent cannot be kept, leaked, subpoenaed or used to train anything. That is a property of how this works, not a promise about how carefully it is run.

Opus and M4A explained

Opus is the current state of the art for lossy audio, and the codec behind most voice calls you make over the internet. It performs well across an unusually wide range, from 6 kbps speech to transparent music.

M4A is an MP4 container holding only audio — usually AAC, sometimes Apple Lossless. The extension exists mainly so players know not to look for a video track.

Where Opus files come from: Voice and video calls, modern podcast pipelines and WebRTC.
Where M4A is used: iTunes purchases, Apple Music downloads, voice memos and audiobooks.

Opus vs M4A

The two formats solve different problems, which is why converting between them involves trade-offs rather than a straight upgrade.

Opus compared with M4A
Property	Source	Target
Compression	Lossy	Lossy or lossless
Introduced	2012	2001
Browser support	Modern browsers and apps; older hardware may not.	Very good, especially on Apple platforms.

Opus is stronger at: Best-in-class quality at low bitrates. Extremely low latency, which is why calls use it. Royalty-free.
M4A is stronger at: Excellent quality per byte. Proper chapter support, which is why audiobooks use it. Strong metadata and artwork handling.

Why convert Opus to M4A?

People make this switch when they run into the limits of Opus: playback on older or embedded hardware. M4A is the better fit when apple ecosystem, audiobooks, or podcasts with chapters.

Opus limitations that prompt the switch: Older hardware and car stereos generally cannot play it. Less recognised by users than MP3.
What you give up: Less universal than MP3 on older or cheaper hardware. The extension hides what codec is actually inside.

Does converting Opus to M4A reduce quality?

M4A compresses without discarding data, but it cannot represent everything an Opus file holds. What does not fit is discarded permanently, so converting the result back will not restore it. Keep the Opus original if it is the only copy.

Measured, not estimated

What converting OPUS to M4A actually costs

On every sample measured, the M4A came out larger — 2.0× larger at best and 3.3× larger at worst.

Each row is one sample chosen to isolate a property these formats treat differently.
Sample	OPUS in	M4A out	Change
An easy clipThe compressible end of the range — a clean tone, or a moving test pattern — where a codec does its best work.	17.8 KB	35.0 KB	+97%
A hard clipThe other end — pink noise, or dense video grain. Close to incompressible by design, and the worst case for every codec.	16.5 KB	54.6 KB	3.3×

Produced by this site's own converter. The same code that runs in your browser, at the same default settings, so these are the bytes you would download.

Samples are generated from a fixed seed rather than taken from real photographs or documents, so the corpus is reproducible and carries no licensing question — and so the numbers predict the shape of your result rather than its exact size. Measured 2026-10-01. The method, and the command that regenerates every figure on this page, are on the how it works page.

About these formats

Source

Opus Audio

The best low-bitrate codec available — voice and music.

Extensions: .opus
MIME type: audio/opus
Best for: Voice calls · Podcasts · Very small files
Compatibility: Modern browsers and apps; older hardware may not.

Target

MPEG-4 Audio

MP4 container holding AAC or ALAC audio.

Extensions: .m4a, .m4b
MIME type: audio/mp4
Best for: iTunes and Apple Music · Audiobooks · Podcasts
Compatibility: Very good, especially on Apple platforms.

Good to know

Opus to M4A Converter — questions

How do I convert Opus to M4A?

Drop your Opus file onto the area above, then press Convert. The M4A file saves straight to your device. You do not need an account, and there is no watermark.

Is it safe to convert Opus files here — are they uploaded to a server?

No, nothing is uploaded. On most online converters, pressing the button copies your file across the internet onto a computer owned by that website; it is converted there and sent back. That copy is what "upload" means, and it is the part that puts your file out of your control. This site does not do it. Your Opus file is read and converted by the browser you are using right now and never leaves this device, so there is no copy for anyone to store, read or hand over. You can prove it: turn off your Wi-Fi after this page loads and the conversion still works.

Can I convert confidential Opus files, like bank statements or contracts?

Yes, and that is the case this site was built for. Because the file never leaves your device, a confidential document is no more exposed than it is sitting in your own folder — there is no transfer, no copy on someone else's hardware, no retention period to read about and no staff with access. Nothing is logged about the file either: not its name, not its size, not its contents. The one thing worth saying plainly is that this protects the file in transit and at rest on our side, not from anything already on your own computer.

Does converting to M4A reduce quality?

M4A uses lossy compression, so some data is discarded. At the default quality the difference is very hard to see or hear; raise the quality setting if you need to be certain, at the cost of a larger file.

How large a file can I convert?

Up to 300 MB per file for this conversion. Because the work happens in your browser, the practical limit is your device's memory — larger files work on a desktop with plenty of RAM and may fail on an older phone.

Can I convert several files at once?

Yes. Add as many as you like and press Convert All. Each file is processed independently, so one failure does not stop the rest, and you can download everything together as a ZIP.

Can I use this on my phone?

Yes. FileTools360 works in mobile browsers on iOS and Android. Pick the file from wherever your phone stores it — Files on iOS, or your downloads folder on Android. Long recordings may run out of memory on an older phone.