Is this OPUS to M4A converter really free?

Yes. Up to 5 files at a time, no signup, no catch. The free tier adds a small watermark to image output — Pro ($9.99/mo or $49/yr) removes it, raises the file size limit to 500 MB, and unlocks unlimited batch conversion.

Are my files uploaded to a server?

No — and you can verify it yourself. Open DevTools → Network tab, then convert a file. You'll see zero upload requests. Everything runs right in your browser. We never see your files.

How long does conversion take?

Usually 1–3 seconds for a typical file. The very first conversion on a fresh page load may take 5–20 seconds while the converter engine loads — after that it's instant. Your CPU does all the work locally.

What is the file size limit?

Free: up to 10 MB per file, 5 files per batch. Pro: up to 500 MB per file, unlimited batch. If you're working with large videos or RAW photos, Pro is built for that.

Can I batch convert multiple OPUS files at once?

Yes — drop multiple files at once (or Ctrl/Cmd+click to select them) and they all convert in parallel. Free accounts handle up to 5 files per batch; Pro has no limit.

What bitrate will the converted audio use?

We default to 192 kbps for MP3, 128 kbps for OGG/Opus, and 320 kbps for M4A/AAC. These settings are perceptually transparent — most listeners can't tell the difference in a blind test.

Will my metadata (ID3 tags, album art) be preserved?

Yes, when both formats support it. Tags carry over on conversions like MP3→M4A or FLAC→MP3. WAV has limited tag support, so some metadata may not transfer.

Why doesn't iOS support Opus?

Apple's audio stack prioritises AAC and ALAC. Opus is an IETF-standard codec used primarily for streaming and WebRTC; while Safari supports Opus for WebRTC, the native Music app and iOS media player don't handle Opus files.

What bitrate should I use for the M4A output?

128–192 kbps AAC is recommended for music transcoded from Opus. Since Opus is already lossy, using a high M4A bitrate minimises the generation loss from re-encoding between two lossy codecs.

How private is this converter?

Completely private — by design, not policy. There is no upload endpoint. Files are processed right inside your browser tab and disappear the moment you close it. We collect only anonymous page-view counts; your file content is never seen or stored.

Opus to M4A Converter — Free, Online, No Upload

How to convert OPUS to M4A online

1
Drop your OPUS file
Drag and drop your Opus Interactive Audio Codec file onto the converter, or click to browse your files. You can select up to 5 at once. Nothing leaves your device — conversion happens right here in the browser.
2
Hit Convert — it happens locally
Click Convert and watch it go. There's no upload, no server queue, no waiting. The converter runs Opus Interactive Audio Codec → MPEG-4 Audio entirely in your browser tab. Most files finish in 1–3 seconds.
3
Download your M4A
Your MPEG-4 Audio file is ready. Click Download, or grab a ZIP if you converted a batch. Close the tab and everything disappears — no copies kept anywhere.

OPUS vs M4A: format overview

OPUS

Opus Interactive Audio Codec

IETF / Xiph.Org · 2012

Compression: lossy
Transparency: No

✓ Best low-bitrate quality of any audio codec
✓ Royalty-free and open standard (RFC 6716)
✗ Not supported on iOS/macOS natively

M4A

MPEG-4 Audio

Apple / MPEG Group · 2001

Compression: lossy
Transparency: No

✓ Better quality than MP3 at same bitrate (AAC codec)
✓ Native Apple ecosystem support

OPUS magic bytes: 4F 67 67 53 (Ogg container)

M4A magic bytes: 00 00 00 xx 66 74 79 70 4D 34 41

Why convert OPUS to M4A?

Opus is the codec inside Discord voice messages, WhatsApp voice notes, Telegram audio, and most WebRTC recordings. It's technically excellent — low latency, efficient compression, widely supported in browsers. But iOS's Music app won't play it, iTunes won't import it, and the native Apple audio stack treats Opus files as unrecognised. When someone sends you a voice note or a Discord bot exports audio and you want to listen to it properly on your Apple devices, Opus is a dead end without conversion.

M4A is Apple's native container for AAC audio and is natively supported by every Apple device made in the last 15 years. Converting Opus to M4A makes the audio playable in the iPhone's native Music app, importable into iTunes, syncable to Apple Watch, and streamable over AirPlay. The conversion involves re-encoding the audio — Opus is decoded and then re-encoded as AAC inside an M4A container — which introduces a small quality reduction inherent to transcoding between lossy codecs.

To minimise the quality impact, the M4A should be output at 128 kbps or higher. At 192 kbps, the difference from the Opus source is negligible in normal listening conditions. The file size will increase compared to the Opus source because AAC is less efficient than Opus at the same perceived quality level — a trade-off for the broad Apple ecosystem compatibility the M4A format provides.

Quality & file size: OPUS to M4A

Typical file sizes: OPUS 1–3 MB → M4A 3–6 MB.

Both OPUS and M4A use lossy compression. We transcode at high quality settings (equivalent to M4A's recommended web quality) to minimize generational loss.

Color depth: OPUS supports standard color, M4A supports standard color.

Transparency: OPUS does not support transparency. M4A does not support transparency — transparent areas become solid white.

Frequently asked questions

Privacy: how FormatDrop handles your files

Your OPUSfiles are converted 100% inside your browser. They are never uploaded to our servers, never stored, and never seen by anyone other than you. This isn't a privacy policy claim — it's an architectural guarantee: our server has no endpoint that receives file bytes.