Javascript Audio play <body onload>

John Papenheim

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Nov 12, 2017, 10:42:21 AM11/12/17

to MIT App Inventor Forum

Hello- Below is a Javascript Function (it's also attached) that generates audio/ modem data to the headphone jack then to Arduino. At the moment, it just sends a bunch of J characters on <body onload> and an i character when a button is pushed <form onsubmit> . (this is so I can hear the difference)

generate() is the main function here...

In browsers like Chrome or Firefox, this script works as expected. However, when I use the App Inventor Web Viewer, the page loads, the

<body onload= "generate('jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj')"> function seems to run, but no sound is played like it does in other browsers. The <form onsubmit="generate('i'); return false;"> plays the expected sound in the web viewer, though.

My eventual goal is to pass data from App Inventor using webview.string to the javascript, then via headphone jack modem to the Arduino... But I need that script to run/ audio to play automatically each time the page is refreshed. In my debuging thus far, it seems to run the generate() function when I do the <body onload>, but the sound does not play.

My app inventor code is just a webviewer and a button to refresh it:

Is there something about the webviewer that is different from other browsers???

Here is the Javascript/ html:

<!DOCTYPE html>

<html>

<head>

<title>FSK Serial Generator in JavaScript for SoftModem board</title>

function chr8() {

return Array.prototype.map.call(arguments, function(a){

return String.fromCharCode(a&0xff)

}).join('');

}

function chr16() {

return Array.prototype.map.call(arguments, function(a){

return String.fromCharCode(a&0xff, (a>>8)&0xff)

}).join('');

}

function chr32() {

return Array.prototype.map.call(arguments, function(a){

return String.fromCharCode(a&0xff, (a>>8)&0xff,(a>>16)&0xff, (a>>24)&0xff);

}).join('');

}

function toUTF8(str) {

var utf8 = [];

for (var i = 0; i < str.length; i++) {

var c = str.charCodeAt(i);

if (c <= 0x7f)

utf8.push(c);

else if (c <= 0x7ff) {

utf8.push(0xc0 | (c >>> 6));

utf8.push(0x80 | (c & 0x3f));

} else if (c <= 0xffff) {

utf8.push(0xe0 | (c >>> 12));

utf8.push(0x80 | ((c >>> 6) & 0x3f));

utf8.push(0x80 | (c & 0x3f));

} else {

var j = 4;

while (c >>> (6*j)) j++;

utf8.push(((0xff00 >>> j) & 0xff) | (c >>> (6*--j)));

while (j--)

utf8[idx++] = 0x80 | ((c >>> (6*j)) & 0x3f);

}

return utf8;

}

var dataURI, audio;

function generate(str) {

if (str.length == 0) return;

var utf8 = toUTF8(str);

//console.log(utf8);

var sampleRate = 29400;

var baud = 1225;

var freqHigh = 7350;

var freqLow = 4900;

var spb = sampleRate/baud; // 24 samples per bit

var preCarrierBits = Math.ceil(sampleRate*40/1000/spb); // 49 bits

var postCarrierBits = Math.ceil(sampleRate*5/1000/spb); // 6.125 bits => 7 bits

var size = (preCarrierBits + postCarrierBits + 10*utf8.length) * spb;

var data = "RIFF" + chr32(size+36) + "WAVE" +

"fmt " + chr32(16, 0x00010001, sampleRate, sampleRate, 0x00080001) +

"data" + chr32(size);

function pushData(freq, samples) {

for (var i = 0; i < samples; i++) {

var v = 128 + 127 * Math.sin((2 * Math.PI) * (i / sampleRate) * freq);

data += chr8(v);

}

pushData(freqHigh, preCarrierBits*spb);

for (var x in utf8) {

var c = (utf8[x] << 1) | 0x200;

for (var i = 0; i < 10; i++, c >>>= 1)

pushData((c&1) ? freqHigh : freqLow, spb);

}

pushData(freqHigh, postCarrierBits*spb);

if (size+44 != data.length) alert("wrong size: " + size+44 + " != " + data.length);

dataURI = "data:audio/wav;base64," + escape(btoa(data));

audio = new Audio(dataURI);

audio.play();

}

</script>

</head>

<h1>Softmodem for Arduino </h1>

</form>

</body>

</html>

fsk-gen.html

John Papenheim

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Nov 12, 2017, 11:24:42 AM11/12/17

to MIT App Inventor Forum

After a bit of research, I do believe this is an Android issue, not an App Inventor issue. It seems Android and other mobile browsers are set up so you cannot auto-play audio or video... presumably to save data costs or prevent your phone from blasting noise in the middle of the night if you left your browser open.

This makes it tough for developers, but there MUST be some work around?