NodeJS - piping multiple FFMPEG processes - node.js

Question

I am trying to programm an converter which can take any video source and convert it to mp3. The mp3 should be saved on my hard drive, or in an buffer to send it via telegram.
It works good so far, the only problem I am facing is that it can only take one video at a time, and I don't know why.
// IMPORTS
var fs = require('fs');
var https = require('https');
var child_process = require('child_process');
// EVENTEMITER (Not used so far)
var util = require('util');
var EventEmitter = require('events').EventEmitter;
// STREAMHANDLER
var StreamHandler = function(url, name){
// VARIABLES
self = this;
this.url = url;
this.name = name;
// CREATE FFMPEG PROCESS
var spawn = child_process.spawn;
var args = ['-i', 'pipe:0', '-f', 'mp3', '-ac', '2', '-ab', '128k', '-acodec', 'libmp3lame', 'pipe:1'];
this.ffmpeg = spawn('ffmpeg', args);
// GRAB STREAM
https.get(url, function(res) {
res.pipe(self.ffmpeg.stdin);
});
// WRITE TO FILE
this.ffmpeg.stdout.pipe(fs.createWriteStream(name));
//DEBUG
this.ffmpeg.stdout.on("data", function (data) {
console.error(self.name);
});
}
util.inherits(StreamHandler, EventEmitter);
// TESTING
var test1 = new StreamHandler(vidUrl, "test1.mp3");
test1.ffmpeg.on("exit", function (code, name, signal) {
console.log("Finished: " + test1.name);
});
var test2 = new StreamHandler(vidUrl, "test2.mp3");
test2.ffmpeg.on("exit", function (code, name, signal) {
console.log("Finished: " + test2.name);
});
It skips test1.mp3 and only converts test2.mp3, but 2 ffmpeg processes were created:
After test2.mp3 is converted the other ffmpeg thread stays open, but does nothing, and the node program gets stuck waiting (i guess so) for it to send something.
I hope someone can help me :)

Answer 1

Using your code, I had the same problem. It would hang at the end and only output data for the test2.mp3 file. I'm not exactly sure what caused the problem, but I changed it a bit and this works for me:
// IMPORTS
var fs = require('fs');
//var https = require('https');
var http = require('http');
var child_process = require('child_process');
// EVENTEMITER (Not used so far)
var util = require('util');
var EventEmitter = require('events').EventEmitter;
// These never change...
var spawn = child_process.spawn;
var args = ['-i', 'pipe:0', '-f', 'mp3', '-ac', '2', '-ab', '128k', '-acodec', 'libmp3lame', 'pipe:1'];
// STREAMHANDLER
var StreamHandler = function(url, name){
// CREATE FFMPEG PROCESS
var ffmpeg = spawn('ffmpeg', args);
// GRAB STREAM
http.get(url, function(res) {
res.pipe(ffmpeg.stdin);
});
// WRITE TO FILE
ffmpeg.stdout.pipe(fs.createWriteStream(name));
ffmpeg.on("exit", function() {
console.log("Finished:", name);
});
//DEBUG
ffmpeg.stdout.on("data", function(data) {
console.error(name, "received data");
});
}
util.inherits(StreamHandler, EventEmitter);
// TESTING
var vidUrl = 'http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_1mb.mp4';
var test1 = new StreamHandler(vidUrl, "test1.mp3");
var test2 = new StreamHandler(vidUrl, "test2.mp3");
I am using http instead of https, because I didn't have a sample video at an https url available. It shouldn't make a difference.
I moved the spawn and args variables out of the object, because they don't change. I also do not use this to store the local variables. I just use a normal closure instead. Finally, I moved the exit event handling code inside the object. I just think it's better to group all that stuff together -- plus, it's only declared once rather than for each new process you create.
Running this gives me the following output (I saved the script as ffmpeg.js):
$ node ffmpeg.js
test2.mp3 received data
Finished: test2.mp3
test1.mp3 received data
Finished: test1.mp3
Also, just a tip. If you want to use the this object inside StreamHandler, I would recommend using arrow functions if your version of Node supports them. This code also works:
var StreamHandler = function(url, name){
// CREATE FFMPEG PROCESS
this.ffmpeg = spawn('ffmpeg', args);
// GRAB STREAM
http.get(url, (res) => {
res.pipe(this.ffmpeg.stdin);
});
// WRITE TO FILE
this.ffmpeg.stdout.pipe(fs.createWriteStream(name));
this.ffmpeg.on("exit", () => {
console.log("Finished:", name);
});
//DEBUG
this.ffmpeg.stdout.on("data", (data) => {
console.error(name, "received data");
});
}
Notice that with arrow functions, I don't have to use var self = this; Avoiding that is pretty much the reason arrow functions were added to javascript.
Hope this helps!
-- EDIT --
Ok, I figured it out. The problem in your code is this line:
self = this;
It should be:
var self = this;
Without the var specifier, you are creating a global variable. So, the second time you are calling new StreamHandler, you are overwriting the self variable. That's why the test1.mp3 file hangs and the test2.mp3 file is the only one finishing. By adding var, your original script now works for me.