batch convert webp to webm, maybe useful for converting Whatsapp sticker to Telegram.

convert.js

/**
require webp & libwebp, see https://developers.google.com/speed/webp/download
run:
cd working_dir # suppose working dir contains all webp that u want to convert
node ./convert.js # wait for it until done
*/
const child = require("child_process");
const fs = require("fs");
const path = require("path");
const util = require("util");
const readdir = util.promisify(fs.readdir);
const exec = util.promisify(child.exec);

const terminateWithError = (error = "[fatal] error") => {
  console.log(error);
  process.exit(1);
};

const converter = (filenames) => {
  const filename = filenames.shift();
  const nameWithoutExt = filename.replace(".webp", "");
  const frames = path.resolve(process.cwd(), "frames");

  if (fs.existsSync(frames)) fs.rmdirSync(frames, { recursive: true });
  fs.mkdirSync(frames);

  process.chdir("frames");
  console.log("[info]", process.cwd());

  console.log("[info]", `anim_dump ../${filename}`);
  exec(`anim_dump ../${filename}`)
    .then(() => {
      process.chdir("..");
      console.log("[info]", process.cwd());

      const command = `webpmux -info ./${filename}`;

      console.log("[info]", command);
      return exec(command);
    })
    .then(({ stdout, stderr }) => {
      if (stderr) return Promise.reject(stderr);

      const isAnimation = stdout.match(/Features present: animation/) !== null;
      if (!isAnimation)
        return Promise.reject("This is not an animated webp file");

      const firstLine = stdout.match(/1:.+[\r]?\n/g);
      if (!firstLine) return;

      const frameLength = firstLine[0].split(/\s+/g)[6];
			console.log('frame length', frameLength)
      const framerate = 11;//Math.round(1000 / frameLength); // frames/second
      const dump = path.resolve(frames, "dump_%04d.png");
      const command = `ffmpeg -framerate ${framerate} -i "${dump}" -crf 0 -b:v 0.8M -b:a 124K "${nameWithoutExt}.webm" -y`;

      console.log("[info]", command);
      return exec(command);
    })
    .then(({ stdout, stderr }) => {
      if (/error/gm.test(stderr)) return Promise.reject(stderr);
      fs.rmdirSync(frames, { recursive: true });
      if (filenames.length != 0) converter(filenames);
      console.log("[info] Success!\n");
    })
    .catch((err) => {
      terminateWithError(`[fatal] ${err}`);
      fs.rmdirSync(frames, { recursive: true });
    });
};

const getWebFiles = async () => {
  let fileName;
  try {
    fileName = await readdir("./");
  } catch (err) {
    console.log(err);
  }
  return fileName.filter((it) => it.endsWith(".webp"));
};

getWebFiles().then((filenames) => {
  converter(filenames);
});