decodeAudioData failing with null errors on continuous stream

Question

In my following code ffmpeg is transcoding the input stream and is successfully sending the chunks to the client. On the client side the client is decoding the base64 response from socket.io and is converting the response to an array buffer. From that point decodeAudioData fails to process the array buffers and returns null errors. Does anyone know why decodeAudioData isn't working?

./webaudio_svr.js:

var express = require('/usr/local/lib/node_modules/express');
var http = require('http');
var spawn = require('child_process').spawn;
var util = require('util');
var fs = require('fs');

var app       = express();
var webServer = http.createServer(app);
var audServer = http.createServer(app);
var io        = require('/usr/local/lib/node_modules/socket.io').listen(webServer, {log: false, });

app.use(express.static(__dirname + '/public'));

app.get('/', function(req, res){
    res.send(
    "<script src='/socket.io/socket.io.js'></script>\n"+
    "<script>var socket=io.connect('http://127.0.0.1:3000');</script>\n"+
    "<script src='/webaudio_cli.js'></script>"
    );
});
webServer.listen(3000);

var inputStream = spawn('/usr/bin/wget', ['-O','-','http://nprdmp.ic.llnwd.net/stream/nprdmp_live01_mp3']);

var ffmpeg = spawn('ffmpeg', [
    '-i', 'pipe:0', // Input on stdin
    '-ar', '44100', // Sampling rate
    '-ac', 2, // Stereo
    '-f', 'mp3',
    'pipe:1' // Output on stdout
]);

io.sockets.on('connection', function(webSocket) {
    var disconnect = '0';

    if (disconnect == '0') {
        inputStream.stdout.pipe(ffmpeg.stdin);
        ffmpeg.stdout.on('data', function(data) {
            var data64 = data.toString('base64');
            webSocket.emit('stream',data64);
        });
    }

    webSocket.on('disconnect', function() {
        disconnect=1;
    });
});

./public/webaudio_cli.js:

function str2ab(str) {
    var buf = new ArrayBuffer(str.length*2); // 2 bytes for each char
    var bufView = new Uint16Array(buf);
    for (var i=0, strLen=str.length; i<strLen; i++) {
        bufView[i] = str.charCodeAt(i);
    }
    return buf;
}

window.AudioContext = window.AudioContext || window.webkitAudioContext;
var context = new AudioContext();
var source = context.createBufferSource();

socket.on('stream', function(data) {
        var data=str2ab(atob(data));
        context.decodeAudioData(data, function(buffer) {
            source.connect(context.destination);
            source.buffer = buffer;
            source.start(0);
        }, function(err) {
            console.log("err(decodeAudioData): "+err);
        });
});

Answer 1

If you read the notes section of the original post you'll see that I ended up getting this working with binaryjs but with the help of Kevin I was able to get this to work with socket.io. Note there this is still a HUGE issue with choppy playback. If someone could lend some assistance to cleaning the audio up please do. This solution is really pointless unless the audio works as expected so I need to figure that out.

The issue has to do with how the browser encodes/decodes your base64 string. Until this is changed you must supply your own functions from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding.

webaudio_svr.js:

var express = require('/usr/local/lib/node_modules/express');
var http = require('http');
var spawn = require('child_process').spawn;
var util = require('util');
var fs = require('fs');

var app       = express();
var webServer = http.createServer(app);
var io        = require('/usr/local/lib/node_modules/socket.io').listen(webServer, {log: false, });

app.use(express.static(__dirname + '/public'));

app.get('/', function(req, res){
    res.send(
    "<script src='/socket.io/socket.io.js'></script>\n"+
    "<script>var socket=io.connect('http://127.0.0.1:3000');</script>\n"+
    "<script src='/base64.js'></script>\n"+
    "<script src='/webaudio_cli.js'></script>"
    );
});
webServer.listen(3000);

var inputStream = spawn('/usr/bin/wget', ['-O','-','http://nprdmp.ic.llnwd.net/stream/nprdmp_live01_mp3']);

var ffmpeg = spawn('ffmpeg', [
    '-i', 'pipe:0', // Input on stdin
    '-ar', '44100', // Sampling rate
    '-ac', 2, // Stereo
    '-f', 'mp3',
    'pipe:1' // Output on stdout
]);

io.sockets.on('connection', function(webSocket) {
    var disconnect = '0';

    if (disconnect == '0') {
        inputStream.stdout.pipe(ffmpeg.stdin);
        ffmpeg.stdout.on('data', function(data) {
            var data64 = data.toString('base64');
            webSocket.emit('stream',data64);
        });
    }

    webSocket.on('disconnect', function() {
        disconnect=1;
    });
});

public/webaudio_cli.js:

window.AudioContext = window.AudioContext || window.webkitAudioContext;
var context = new AudioContext();
var startTime = context.currentTime;

// buffer to arraybuffer
function toArrayBuffer(buffer) {
    var ab = new ArrayBuffer(buffer.length);
    var view = new Uint8Array(ab);
    for (var i = 0; i < buffer.length; ++i) {
    view[i] = buffer[i];
    }
    return ab;
}
socket.on('stream', function(data) {
        var data=toArrayBuffer(base64DecToArr(data));
        context.decodeAudioData(data, function(buffer) {
            playBuffer(buffer);
        }, function(err) {
            console.log("decodeAudioData err: "+err);
        });
});

function playBuffer(buf) {
    var source    = context.createBufferSource();
    source.buffer = buf;
    source.connect(context.destination);
    source.start(startTime);
    startTime = startTime+source.buffer.duration;
}

public/base64.js:

• copy and paste functions from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding#Solution_.232_.E2.80.93_rewriting_atob()_and_btoa()_using_TypedArrays_and_UTF-8