Is this MP4 to OPUS 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 MP4 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.

What bitrate should I use for MP4 to Opus?

For music audio, 96–128 kbps Opus is perceptually transparent. For voice or podcast content from a video, 32–64 kbps is sufficient and sounds excellent.

Can I play Opus files on my phone?

Android supports Opus natively. On iPhone, Opus playback requires a third-party app like VLC — the native iOS Music app does not support Opus.

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.

MP4 to Opus Converter — Free, Online, No Upload

How to convert MP4 to OPUS online

1
Drop your MP4 file
Drag and drop your MPEG-4 Part 14 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 MPEG-4 Part 14 → Opus Interactive Audio Codec entirely in your browser tab. Most files finish in 1–3 seconds.
3
Download your OPUS
Your Opus Interactive Audio Codec file is ready. Click Download, or grab a ZIP if you converted a batch. Close the tab and everything disappears — no copies kept anywhere.

MP4 vs OPUS: format overview

MP4

MPEG-4 Part 14

Moving Picture Experts Group · 2001

Compression: lossy
Transparency: No

✓ Universal compatibility across all platforms
✓ Excellent compression with H.264/H.265
✗ H.264 has royalty implications

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)

MP4 magic bytes: 00 00 00 xx 66 74 79 70

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

Why convert MP4 to OPUS?

You've got a video — a recorded meeting, a podcast video, a voice memo captured as MP4 — and you need to deliver the audio over the internet with the smallest possible file size. MP3 is old technology. AAC is patented. Opus is the modern answer: a royalty-free codec engineered specifically for streaming, VoIP, and web delivery, and it outperforms both MP3 and AAC at every bitrate below 128 kbps.

This converter extracts the audio from your MP4 and re-encodes it as Opus. Discord uses Opus for voice. WebRTC (the technology behind browser-based video calls) uses Opus. Chromium-based browsers play Opus in HTML5 audio elements natively. For a recorded meeting at 48 kbps or a music track at 96 kbps, Opus produces cleaner audio than MP3 at twice the bitrate — making it ideal for podcast streaming, web audio, and Discord bots.

Because the MP4's AAC audio is re-encoded into Opus, there is a generation loss. Use the highest bitrate you can afford for your use case: 32–48 kbps for clear voice, 96–128 kbps for music. The output file is a standard .opus container that plays in Chrome, Firefox, Edge, Android, and VLC. Safari and the native iOS Music app do not support Opus playback.

Quality & file size: MP4 to OPUS

Typical file sizes: MP4 100–300 MB → OPUS 1–3 MB.

Both MP4 and OPUS use lossy compression. We transcode at high quality settings (equivalent to OPUS's recommended web quality) to minimize generational loss.

Color depth: MP4 supports standard color, OPUS supports standard color.

Transparency: MP4 does not support transparency. OPUS does not support transparency — transparent areas become solid white.

Frequently asked questions

Privacy: how FormatDrop handles your files

Your MP4files 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.