M4A to MP3

How do I convert M4A to MP3?

1. Drop your M4A or AAC files onto the drop zone, or click to browse. iPhone Voice Memos shared to your computer arrive as M4A and work as they are.
2. Choose an MP3 bitrate: 128 kbps (small) for voice memos and podcasts, 192 kbps (good) for music.
3. Click Convert to MP3.
4. Wait a few seconds per file.
5. Download each MP3, or Download all as ZIP for a batch.

M4A is an MPEG-4 container holding AAC audio, the format Apple uses for Voice Memos, iTunes purchases and Music app rips, and the same audio codec found inside most MP4 videos. It is a good format, but plenty of things still refuse it: older car stereos, some Android messaging apps, transcription services, WordPress uploads and many podcast hosts want MP3. This tool decodes the AAC with FFmpeg and re-encodes it with the LAME MP3 encoder at the bitrate you choose.

Because both AAC and MP3 are lossy, converting between them loses a little quality: the MP3 encoder cannot recover detail the AAC encoder already removed, and it discards a little more of its own. Choosing a bitrate at or above the original avoids making it worse than necessary. Voice memos are recorded at 64 kbps AAC, so 128 kbps MP3 is generous; music from Apple at 256 kbps AAC is best converted at 256 or 320 kbps if you care about the last percent.

The job is quick. Audio decoding and encoding are light, so a 10 minute voice memo converts in a few seconds on a laptop and well under a minute on a phone, and a 60 minute lecture in under a minute on most hardware. Batch mode handles a folder of memos in one go and bundles them into a ZIP. Files with .aac extensions, which are raw AAC streams rather than M4A containers, are accepted too.

Everything happens in your browser. FFmpeg compiled to WebAssembly is downloaded once (about 30 MB) and cached, so later conversions work offline, and no audio is ever uploaded. That matters for voice memos, which are often private: meeting notes, medical appointments, interviews. Files up to about 1 GB are comfortable and the browser's roughly 2 GB WebAssembly memory limit is the ceiling, well beyond any recording a phone produces.

How it works: this tool uses FFmpeg compiled to WebAssembly (ffmpeg.wasm), loaded into your browser. No server is involved, so Kilnfile never sees your file. Last reviewed 20 September 2026.

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