Turn an MP3 into an efficient Opus file using your browser's native encoder — smaller than MP3 at the same quality.
The MP3 to Opus converter turns MP3 audio (MPEG-1/2 Layer III) into Opus (Opus (RFC 6716), usually in an Ogg or WebM container) directly in your browser. Opus gives the best quality for the size, especially for speech, and is the codec behind WhatsApp voice notes and Discord.
MP3 is the most universally supported lossy format; plays on virtually every phone, car stereo, browser and editor. Opus is the most efficient modern codec for speech and music, used by WhatsApp voice notes, Discord, YouTube and WebRTC; transparent quality from about 96 kbps. Both MP3 and Opus are lossy, so this is a transcode: some extra quality is lost. Pick a bitrate at or above the original’s to limit the damage, and keep the original file.
Your file is decoded to 32-bit floating-point samples by the browser’s own audio decoder — and at the file’s own sample rate, not a resampled one. You can optionally resample or switch channels. It is then encoded to Opus on your device; for a lossy target the result is decoded again for the preview, so you hear what you will get. Typical size: about 0.7 MB per minute at 96 kbps.
Source format facts: MP3 files are lossy; usual bandwidth: typically low-passed at 16–20 kHz depending on bitrate. Target facts: Opus is lossy; usual bandwidth: up to 20 kHz (fullband).
Tiny, clear speech files.
Open, efficient streaming.
Low-latency format.
Smallest files at good quality.
| From | MP3 — MPEG-1/2 Layer III |
|---|---|
| To | Opus — Opus (RFC 6716), usually in an Ogg or WebM container |
| Direction | lossy → lossy |
| Typical size | about 0.7 MB per minute at 96 kbps |
| Tags | MP3: ID3 → Opus: Opus tags |
It is the most efficient general-purpose codec.
WhatsApp voice notes use Opus in Ogg; share via document if audio picking fails.
Whichever container your browser's Opus encoder actually produces — usually .ogg or .webm, shown clearly before you download.
Going to WAV is lossless. Going to MP3 uses a standard 192kbps encode by default (adjustable), which is transparent for most listening but is a lossy step if your source was uncompressed.
No — the file is decoded and re-encoded entirely in your browser using the Web Audio API and, for MP3, a small bundled encoder. Nothing is sent anywhere.
This tool runs entirely in your browser using the Web Audio API. Nothing is uploaded, stored or shared — there is no server to send your file to, so it works offline once the page has loaded.
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