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Reading waveform data in ffmpeg

When working on an audio player, I wanted to extract the audio waveform data to paint the audio waveform dynamically in the browser on a <canvas> element.

Initially I used the bbc/audiowaveform package but this proved problematic for a number of reasons. First I wasn't able to install that package (or build the binary) in macOS for local dev. The other big issue is that I was only able to figure out how to install it on Ubuntu, so I couldn't use it in Alpine (for Docker images) or other environments like cloud functions.

Initial approach

I found out from these docs it's possible to paint a waveform with ffmpeg by extracting raw audio data:

Using Svelte in a Vercel serverless function

The easiest way of using Svelte for SSR in Node is by using svelte/register. This allows to require .svelte files without any bundling and render HTML, CSS, etc.

This is the example from the docs:

require('svelte/register');

const App = require('./App.svelte').default;

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	const elements = [];
	const events = [];

	window.addEventListener('pageshow', (event) => {
	const navigationType = window.performance.getEntriesByType('navigation')[0].type;
	if (navigationType !== 'back_forward') return;

	elements.forEach((element, index) => {
	element.dispatchEvent(new Event(events[index], {
	bubbles: true,

	const cache = caches.default;

	addEventListener("fetch", (event) => {
	try {
	const request = event.request
	return event.respondWith(handleRequest(event))
	} catch (e) {
	return event.respondWith(new Response("Error thrown " + e.message))
	}
	});

	<script>
	import keepAlive from "./action.js";
	import Component from './Component.svelte';
	</script>

	<div use:keepAlive={{id: 'some-manual-id', componentClass: Component}}/>

	CreateFunction({
	name: 'GetIndexValuesObject',
	body: Query(
	Lambda(
	['indexRef', 'indexValuesArray'],
	Let(
	{
	keys: Let(
	{
	indexDoc: Get(Var('indexRef')),

	openssl req -x509 -newkey rsa:2048 -nodes -sha256 -subj '/CN=localhost' -keyout localhost-key.pem -out localhost-cert.pem
	mkcert -install
	mkcert -key-file localhost-key.pem -cert-file localhost-cert.pem mydevdomain.com localhost 127.0.0.1