Piping streams through a shell program (ffmpeg) and writing the output to a file

import { extname } from 'https://deno.land/std/path/mod.ts';
const input_file = `./sample_recording.wav`;
const ffmpeg_bin = `/usr/bin/ffmpeg`;
const output_file = './sample_output.ogg';

const input_data = await Deno.open(input_file, { read: true });

const command = new Deno.Command(ffmpeg_bin, {
  args: [
    '-i', '-',
  ],
  stdin: 'piped',
  stdout: 'piped',
});

const childProcess = command.spawn();

childProcess.stdout.pipeTo(
  Deno.openSync(output_file, { write: true, create: true }).writable,
);

childProcess.stdin.close();

input_data.close();