My app is supposed to take Web Audio streamed from the client, encode it as MP3, before sending it back out to clients via WebSocket.

I can currently encode and pipe to a file like this:

inbound_stream.pipe(encoder).pipe(fs.createWriteStream('audio.mp3'));

And if I already have a file on the server I can do this:

var mp3File = fs.createReadStream('audio.mp3');

            mp3File.on('data', function(buffer){
                io.sockets.emit('audio', { buffer: buffer });
            });

However, I want to access the encoded chunks in real time, and send those out to clients - not write to a file.

What I want is this, effectively:

inbound_stream.pipe(encoder).pipe(newReadStream);

        newReadStream.on('data', function(buffer){
            io.sockets.emit('audio', { buffer: buffer });
        });

I've looked at Duplex and Transform streams, but frankly I am still learning and the Prototyping made my head spin.

How do I do this? Thanks.

UPDATE

The solution below from @Nazar Sakharenko certainly does what I wanted, but the overhead of live encoding seems to make this inpossible, so writing the encoded MP3, and pre-buffering it seems to be the only way (thanks to various people for the suggestion.)

However I still have problems with this approach. New question here:

node.js - create a new ReadStream for a new file, when that file reaches a certain size

According to documentation readable.pipe(destination[, options]) the destination should be stream.Writable.

What you can do is to implement your own Writable stream:

const Writable = require('stream').Writable;

var buffer = [];
//in bytes
const CHUNK_SIZE = 102400; //100kb

const myWritable = new Writable({
  write(chunk, encoding, callback) {
    buffer += chunk;
    if(buffer.length >= CHUNK_SIZE) {
       io.sockets.emit('audio', { buffer: buffer});
       buffer = [];
    }

    callback();
  }
});

myWritable.on('finish', () => {
   //emit final part if there is data to emit
   if(buffer.length) {
       io.sockets.emit('audio', { buffer: buffer});
   }
});


inbound_stream.pipe(encoder).pipe(myWritable);

thats all.