Audio normalize (EBU R128)

Loudness-normalize any audio/video URL to a target LUFS with ffmpeg's loudnorm (EBU R128) and return MP3 - consistent levels for podcasts, clips, and TTS output. Send POST /api/audio-normalize with the required field url and pay $0.02 per call over x402 or MPP (there is no free tier). It returns a JSON object with format, targetLufs, truePeakDb, bytes and mp3Base64.

Body: {"url":"https://…/audio.wav","targetLufs":-16?}.

Category: Web & documents · Tags: ffmpeg normalize loudnorm audio lufs

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/audio-normalize \
  -H "Content-Type: application/json" \
  -d '{"url":"https://agent402.tools/fixtures/sample-audio.wav"}'

Without payment this returns HTTP 402 Payment Required with the exact price for audio-normalize; any x402 v2 or MPP client pays it and retries.

Example response

{
  "format": "mp3",
  "targetLufs": -16,
  "truePeakDb": -1.5,
  "bytes": 49581,
  "mp3Base64": "SUQzBAAAAA…"
}

From an MCP client

catalog.call {
  "slug": "audio-normalize",
  "params": {
    "url": "https://agent402.tools/fixtures/sample-audio.wav"
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for audio-normalize; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• url is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Wallet-only: this tool reaches the network or stored state, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• A GET or HEAD to /api/audio-normalize returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/audio-normalize", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "url": "https://agent402.tools/fixtures/sample-audio.wav"
  }),
});

Part of these workflows

Audio normalize (EBU R128) is one step in this skill pack, each sold as a single call:

• Uploaded-media normalize - The 'user uploaded a thing, normalize it before storing' workflow. Probe the file (image or audio/video) with media-info, decode any embedded barcodes/QRs, resize and thumbnail the image, convert it to a web-friendly format, and normalize audio loudness to broadcast standard. Six tools, one canonical normalize-on-upload pipeline that turns arbitrary user uploads into predictable storage artifacts.

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