Convert M4A to Opus online

Your M4A file is converted to Opus right here in your browser, using FFmpeg compiled to WebAssembly. Nothing is uploaded to us, the audio never leaves your device. Quality is preserved and the download is ready in seconds.

What is an M4A file?

M4A is the MPEG-4 audio container, almost always holding AAC-encoded audio. It is what an iPhone produces: Voice Memos, iTunes purchases and most Apple-ecosystem audio are M4A files.

iPhone Voice Memos records M4A, which makes it one of the most common interview and meeting formats in the real world. Many Android recorder apps also default to it.

Why Opus?

Opus is the newest major audio codec (standardised in 2012) and the best-in-class at speech and low bitrates. Which is exactly why WhatsApp voice notes are Opus files. It was designed for real-time internet audio and it is what Discord, WhatsApp and most VoIP apps use.

Convert to Opus for the smallest possible file that still sounds clear, voice at 32 kbps Opus sounds better than at double the bitrate in MP3. Ideal for sharing long voice recordings over limited data. M4A support outside the Apple world is good but not universal, some older car stereos, players and upload forms only take MP3 or WAV.

Frequently asked questions

Will converting M4A to Opus lose quality?

A small, one-time generational loss is unavoidable. Both M4A and Opus are lossy, so re-encoding discards a little more detail. The converter uses high-quality settings to keep it inaudible for speech, but if you still have the original uncompressed source, converting from that instead is always better.

Is it free?

Yes, completely, with no account and no watermark. The conversion runs on your own device, so it costs us nothing to let you use it. The only limit is file size: up to 50 MB, which is what a browser can hold in memory comfortably.

Do I need to install anything, or upload my file?

Neither. It runs entirely in your browser using FFmpeg compiled to WebAssembly. Your audio is never sent to us, which is also why it works on a slow connection, only the page downloads, not your file.

Need a transcript of the audio?

Autrans also transcribes audio in Nigerian English, Pidgin, Yoruba, Hausa, Igbo, French, and Spanish.