How do I convert M4A to Opus?

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

Are my files uploaded to a server?

No. This conversion runs entirely inside your browser using WebAssembly, so the file never leaves your device — you can even disconnect from the internet after the page loads and it will still work.

Does converting to Opus reduce quality?

Opus 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, including choosing files straight from your camera roll. Very large videos may run out of memory on a phone — those are better converted on a laptop.

AudioAdjustable qualityRuns in your browser

M4A to Opus Converter

Turn M4A files into Opus in a couple of clicks. MP4 container holding AAC or ALAC audio. The best low-bitrate codec available — voice and music. The output is re-encoded, so quality depends on the settings you choose.

On your deviceNever uploadedGone when you close the tabHow this works

Drop your files here

M4A files (.m4a, .m4b) · up to 300 MB each

or paste files from your clipboard

Ready when you are

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

⌘K to search converters

How to use it

1
Add your M4A files
Drag them onto the upload area, choose them from your device, or paste them from your clipboard. You can queue several at once.
2
Adjust the settings if you want to
The defaults suit most people. Open Advanced to control bitrate, sample rate and channels and start and end times.
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.

M4A and Opus explained

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.

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.

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

M4A vs Opus

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

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

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

Why convert M4A to Opus?

People make this switch when they run into the limits of M4A: you need certainty that any device will play it. Opus is the better fit when voice content, or any situation where bandwidth is tight.

M4A limitations that prompt the switch: Less universal than MP3 on older or cheaper hardware. The extension hides what codec is actually inside.
What you give up: Older hardware and car stereos generally cannot play it. Less recognised by users than MP3.

Does converting M4A to Opus reduce quality?

M4A stores your data exactly; Opus does not. Some detail is discarded permanently in exchange for a much smaller file, which is usually the right trade for sharing and publishing. Keep your M4A original if it is the only copy — the conversion cannot be undone.