WEBM to M4A

How to do it

1. Download Asteria and open it. It's free and needs no account.
2. Drop your WEBM files onto its window, or press ⌘O (Ctrl O on Windows) to choose them. Drop as many as you like.
3. Type m4aand pick Convert to M4A. AAC audio.
4. The first time, Asteria asks to download FFmpeg, a free add-on from the FFmpeg project, under the GPL-3.0-or-later license. It shows the download size before you say yes, and needs no administrator password.
5. Press ⌘↵ (Ctrl ↵ on Windows) to save. The M4A files appear next to the originals, which stay exactly as they were.

What it needs

WEBM to M4A uses FFmpeg, a free program for audio and video. Asteria doesn't bundle it. The first time you need it, Asteria offers to download it, checks the download against a pinned checksum, and keeps it in its own folder, where Settings can remove it again. If FFmpeg is already on your computer, Asteria uses that copy.

How it was tested

A real WEBM file was converted on macOS on Apple silicon and Linux, and the M4A that came out was opened and checked with ffprobe to make sure it is what it says it is.

Other ways to get there

These skills also take a WEBM and give back a M4A: Extract Audio.