A pure JavaScript Node library for recording a screencast of a webpage and returning an animated PNG (APNG) file of the screencast. APNG is supported in Firefox, Chrome, Safari and in the Chrome-based version of Edge. Also, GitHub will play animated PNGs in readmes and other MarkDown documents, no problem.

npm install tomashubelbauer/node-puppeteer-apng

const buffer = await nodePuppeteerApng('https://google.com/ncr');
await fs.writeFile(`screencast.png`, buffer);

const buffer = await nodePuppeteerApng(async (start, stop) => {
  const browser = await puppeteer.launch();
  const [page] = await browser.pages();
  await page.goto('https://www.youtube.com/watch?v=jNQXAC9IVRw');
  const playButton = await page.waitForSelector('.ytp-large-play-button');
  await playButton.click();
  await start(page);
  await page.waitFor(5000);
  await stop();
  await browser.close();
});

await fs.writeFile(`screencast.png`, buffer);

And if I can do something about that or if it is a Puppeteer thing.

Without shelling out to native binaries. Probably the best way to do this would be to study how the quantization and palette generation is done in PNG, then scan all the PNGs and collect all the colors, quantize them and replace them in the true color PNG, then rewrite all the individual PNGs to refer to the same palette, then keep the palette from the first PNG knowing the subsequent ones will have correct indices into it as well.