Yout: L-Internet DVR

import requests, base64

video = base64.b64encode(b"https://youtu.be/kXxvV5KKNfM").decode()

r = requests.post(
    "https://dvr.yout.com/mp3",
    headers={"Authorization": "API_KEY"},
    data={"video_url": video, "audio_quality": "320k"},
)

with open("audio.mp3", "wb") as f:
    f.write(r.content)

curl -X POST "https://dvr.yout.com/mp3" \
  -H "Authorization: API_KEY" \
  --data-urlencode "video_url=$(echo -n 'https://youtu.be/kXxvV5KKNfM' | base64)" \
  --data-urlencode "audio_quality=320k" \
  --output audio.mp3

const video = Buffer.from("https://youtu.be/kXxvV5KKNfM").toString("base64");

const body = new URLSearchParams({ video_url: video, audio_quality: "320k" });

const r = await fetch("https://dvr.yout.com/mp3", {
  method: "POST",
  headers: { Authorization: "API_KEY" },
  body,
});

const buf = Buffer.from(await r.arrayBuffer());
fs.writeFileSync("audio.mp3", buf);