If it’s just an experiment, then you probably can send the captured packets over websocket to the elixir app, and process it there either with ffmpeg or “manually” in elixir/erlang (to write to a container like mp3). For the latter you might want to check out the (outdated and abandoned) erlyvideo repo. There’s also GitHub - membraneframework/membrane_core: The core of Membrane Framework, multimedia processing framework written in Elixir · GitHub which seems like a wrapper for ffmpeg, but I haven’t used it yet.

In a more serious project you’d probably want to use webrtc (to make use of udp instead of tcp) to send audio (or any form of real time media) from the browser to the server.

Do you want to use a browser to capture the audio or elixir (with a nif, most likely)?