Stream audio simultaneously from soundcloud source with node

Question

I am using the Soundcloud api from a node server. I want to stream an audio track simultaneously to multiple users.

I tried something like this (using the code on this question Streaming audio from a Node.js server to HTML5 <audio> tag) but it does not work. Any idea on how I could do this?

var radio = require("radio-stream");
var http = require('http');
var url = "http://api.soundcloud.com/tracks/79031167/stream?client_id=db10c5086fe237d1718f7a5184f33b51";
var stream = radio.createReadStream(url);

var clients = [];

stream.on("connect", function() {
    console.error("Radio Stream connected!");
    console.error(stream.headers);
});

stream.on("data", function (chunk) {
    if (clients.length > 0){
        for (client in clients){
            clients[client].write(chunk);
        };
    }
});

stream.on("metadata", function(title) {
    console.error(title);
});

var server = http.createServer(function(req, res){
    res.writeHead(200,{
        "Content-Type": "audio/mpeg",
        'Transfer-Encoding': 'chunked'
    });

    clients.push(res);
    console.log('Client connected; streaming');
});
server.listen("8000", "0.0.0.0");

console.log('Server running at http://127.0.0.1:8000'); 

Answer 1

There are several problems

Follow Redirects

The radio-stream module that you're using hasn't been updated in 4 years. That's an eternity in Node.js API's time. I recommend not using it, as there are undoubtedly compatibility issues with current and future versions of Node.js. At a minimum, there are much better ways of handling this now with the new streams API.

In any case, that module does not follow HTTP redirects. The SoundCloud API is redirecting you to the actual media file.

Besides, the radio-stream module is built to demux SHOUTcast/Icecast style metadata, not MP3 ID3 data. It won't help you.

All you need is a simple http.get(). You can then either follow the redirect yourself, or use the request package. More here: How do you follow an HTTP Redirect in Node.js?

Chunked Encoding

Many streaming clients cannot deal with chunked encoding. Node.js (correctly) adds it when you have streaming output. For our purposes though, let's disable it.

res.useChunkedEncodingByDefault = false;

https://stackoverflow.com/a/11589937/362536

Building a Coherent Stream

In theory, you can just append MPEG stream after MPEG stream and all will work fine. In practice, this doesn't work. ID3 tags will corrupt the stream. One file might be in a different sample rate than the other file and most software will not be able to switch the hardware to that new sample rate on the fly. Basically, you cannot reliably do what you're trying to do.

The only thing you can do is re-encode the entire stream by playing back these audio files, and getting a solid stream out the other end. This gives you the added bonus that you can handle other codecs and formats, not just MP3.

To handle many of your codec issues, you can utilize FFmpeg. However, you're going to need a way to play back those files to FFmpeg for encoding.

Rate Limiting

You must stream audio at the rate of playback. (You can send an initial buffer to get clients started quickly, but you can't keep slamming data to them as fast as possible.) If you don't do this, you will run out of memory on the server very quickly, as clients will lower their TCP window size down to zero and stay there until the audio has caught up enough to allow buffering more data. Since you're not using pipe, your streams are in flowing mode and will indefinitely buffer on the server. Now, this is actually a good thing in some ways because that prevents one slow client from slowing down the others. It's a bad thing though in that your code, you are streaming as fast as possible and not at the rate of playback.

If you play back the audio to another encoder, use RTC over several seconds as a clock. It doesn't have to be perfect, that's what client buffers are for. If you're playing back to an audio device, it has its own clock of course, which will be used.

What you should actually do

You've stumbled into a huge project. I strongly recommend using Liquidsoap instead. There are ways you can control it from Node.js. From there, use a server like Icecast for your streaming.