Normalizing audio levels

Ideally, you use the audio loudness meter in the Recording interface to ensure that the audio levels are consistent across recordings.

If you need to do equalize the audio levels after the fact, you can use the following script:

note

This is a destructive action - your recordings will be overwritten.
Commit your changes before you run this.

normalize.ts
tsx
import { $ } from "bun";
import { renameSync } from "fs";
import { WEBCAM_PREFIX } from "./config/cameras";
type FfmpegVolumeOutput = {
  input_i: string;
  input_tp: string;
  input_lra: string;
  input_thresh: string;
  output_i: string;
  output_tp: string;
  output_lra: string;
  output_thresh: string;
  normalization_type: string;
  target_offset: string;
};
// Set your composition ID here
const id = "euro";
const files = await $`ls public/${id}`.quiet();
const webcamFiles = files.stdout
  .toString("utf8")
  .split("\n")
  .filter((f) => f.startsWith(WEBCAM_PREFIX));
const decibelValues: number[] = [];
for (const file of webcamFiles) {
  const path = `public/${id}/${file}`;
  const cmd =
    await $`ffmpeg -hide_banner -i ${path} -af loudnorm=I=-23:LRA=7:print_format=json -f null -`.quiet();
  const output = cmd.stderr.toString("utf8");
  const lines = output.split("\n");
  const indexOfLineBeforeStart = lines.findIndex((line) =>
    line.includes("[Parsed_loudnorm_0 @"),
  );
  const remaining = lines.slice(indexOfLineBeforeStart + 1);
  const indexOfOut = remaining.findIndex((i) => i.startsWith("[out#0"));
  const actual = indexOfOut === -1 ? remaining : remaining.slice(0, indexOfOut);
  const json = JSON.parse(actual.join("\n")) as FfmpegVolumeOutput;
  console.log(path, `${json.input_i}dB`);
  decibelValues.push(parseFloat(json.input_i));
}
const average = decibelValues.reduce((a, b) => a + b, 0) / decibelValues.length;
console.log("Average", `${average}dB`);
const toApply = Math.max(average, -20);
console.log("Applying", `${toApply}dB`);
for (const file of webcamFiles) {
  const path = `public/${id}/${file}`;
  const copiedPath = `public/${id}/normalized-${file}`;
  await $`ffmpeg -hide_banner -i ${path} -af loudnorm=I=${toApply}:LRA=7:TP=-2.0 -c:v copy ${copiedPath} -y`;
  renameSync(copiedPath, path);
}

normalize.ts
tsx
import { $ } from "bun";
import { renameSync } from "fs";
import { WEBCAM_PREFIX } from "./config/cameras";
type FfmpegVolumeOutput = {
  input_i: string;
  input_tp: string;
  input_lra: string;
  input_thresh: string;
  output_i: string;
  output_tp: string;
  output_lra: string;
  output_thresh: string;
  normalization_type: string;
  target_offset: string;
};
// Set your composition ID here
const id = "euro";
const files = await $`ls public/${id}`.quiet();
const webcamFiles = files.stdout
  .toString("utf8")
  .split("\n")
  .filter((f) => f.startsWith(WEBCAM_PREFIX));
const decibelValues: number[] = [];
for (const file of webcamFiles) {
  const path = `public/${id}/${file}`;
  const cmd =
    await $`ffmpeg -hide_banner -i ${path} -af loudnorm=I=-23:LRA=7:print_format=json -f null -`.quiet();
  const output = cmd.stderr.toString("utf8");
  const lines = output.split("\n");
  const indexOfLineBeforeStart = lines.findIndex((line) =>
    line.includes("[Parsed_loudnorm_0 @"),
  );
  const remaining = lines.slice(indexOfLineBeforeStart + 1);
  const indexOfOut = remaining.findIndex((i) => i.startsWith("[out#0"));
  const actual = indexOfOut === -1 ? remaining : remaining.slice(0, indexOfOut);
  const json = JSON.parse(actual.join("\n")) as FfmpegVolumeOutput;
  console.log(path, `${json.input_i}dB`);
  decibelValues.push(parseFloat(json.input_i));
}
const average = decibelValues.reduce((a, b) => a + b, 0) / decibelValues.length;
console.log("Average", `${average}dB`);
const toApply = Math.max(average, -20);
console.log("Applying", `${toApply}dB`);
for (const file of webcamFiles) {
  const path = `public/${id}/${file}`;
  const copiedPath = `public/${id}/normalized-${file}`;
  await $`ffmpeg -hide_banner -i ${path} -af loudnorm=I=${toApply}:LRA=7:TP=-2.0 -c:v copy ${copiedPath} -y`;
  renameSync(copiedPath, path);
}

This will calculate the average loudness of all recordings and edit each file so it has the same loudness as the average.

Execute it using:

shell
bun normalize.ts

shell
bun normalize.ts