Convert MP4 to M4A Online

"Online converter" normally means uploading your file to someone's server, waiting in a queue, and downloading the result. This page inverts that: it loads FFmpeg compiled to WebAssembly into your browser and does the work on your own machine. You keep the convenience of online — nothing to install, works on any OS — without the upload.

Expect roughly 50× smaller: MP4 runs about 60 MB per minute, M4A about 1.2. That matters here, because transfer is where server-based converters spend most of their time. With no upload and no download of the result, what's left is just the conversion itself: usually a second or two.

MP4 files typically come from phone video, recorded webinars and lectures, downloaded clips, and screen captures — and the video stream is nearly the entire file, so extracting the audio collapses a 500 MB video into a few MB. Both MP4 and M4A are lossy, so this is a second-generation encode — it can't add anything back. Use 192 kbps or above and the extra loss stays inaudible.

Because it's a web page rather than software, the same converter runs on Windows, macOS, Linux, ChromeOS, iPhone, and Android — with nothing to keep updated and none of the bundled adware that comes with downloadable free converters.

MP4 files come from phone video, recorded webinars and lectures, downloaded clips, and screen captures. The video stream is nearly the entire file, so extracting the audio collapses a 500 MB video into a few MB — which is the whole reason this conversion exists. M4A is the destination because it plays essentially everywhere — iPhone Voice Memos and every ordinary phone, browser, and player. Expect roughly 50× smaller: MP4 runs about 60 MB per minute, M4A about 1.2. Both MP4 and M4A are lossy, so this pair stacks a second encode — at a generous bitrate it stays inaudible, but if a lossless original of the MP4 exists, encode the M4A from that instead.