headless-gl-movie.mjs

import { promises as fs } from "fs";

import createContext from "gl";
import beamcoder from "beamcoder";

const w = 100, h = 100;

async function main() {

  const decoder = beamcoder.decoder({
    name: "rawvideo",
    pix_fmt: 'rgba',
    width: w,
    height: h,
  });

  const encoder = beamcoder.encoder({
    name : 'mjpeg',
    width : w,
    height: h,
    pix_fmt: 'yuvj444p', 
    time_base: [1, 1]
  });

  const filterer = await beamcoder.filterer({
    filterType: 'video',
    inputParams: [
      {
        width: w,
        height: h,
        pixelFormat: 'uyvy422',
        pixelAspect: [1, 1],
        timeBase: [1, 1]
      }
    ],
    outputParams: [
      {
        pixelFormat: 'yuvj444p'
      }
    ],
    filterSpec: 'format=pix_fmts=yuvj422p'
  });

  const gl = createContext(w, h, { preserveDrawingBuffer: true });

  gl.clearColor(1, 0, 0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);

  const b = new Uint8Array(w * h * 4);
  gl.readPixels(0, 0, w, h, gl.RGBA, gl.UNSIGNED_BYTE, b);

  const packet = beamcoder.packet({
    data: Buffer.from(b),
    size: w * h * 4
  });

  const decoded = await decoder.decode(packet);
  const frame = decoded.frames[0];
  const filtered = await filterer.filter([frame]);
  const encoded = await encoder.encode(filtered[0].frames[0]);
  await encoder.flush();
  await fs.writeFile("output.jpg", encoded.packets[0].data);
};

main();