dr.benchi Posts

dr.benchi

•Created by dr.benchi on 9/7/2023 in #help

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

I've been trying to use ffmpeg on the backend of my super simple audio-uploading app. I can save the files as-uploaded, but after getting a Reader for the uploaded file I can't figure out how to pipe it into Deno.Command. The examples on the website don't quite capture my use case (the example shows piping output, but I can't get the magic combination to pipe in input that doesn't make it choke. I've got it working fine if I save the uploaded file to filesystem first and then pass its path to ffmpeg, but that's a hack, surely I can do this with just the streams? Part of this is just me trying to understand the difference between command.output() and command.spawn() and then accessing the stdi/o streams. Literally following the example from the web eg:

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();

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();

This results in pipe:: Invalid data found when processing input and creates an empty output file. However this file gets processed fine if passed as a file path... What am I missing/misunderstanding?

3 replies