apple2js/js/ui/tape.js

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2019-01-09 08:27:31 +00:00
/*globals debug */
/*exported Tape */
function Tape(io) {
var AudioContext = window.AudioContext || window.webkitAudioContext;
return {
doLoadLocalTape: function(file, done) {
var kHz = io.getHz() / 1000;
// Audio Buffer Source
var context;
if (AudioContext) {
context = new AudioContext();
} else {
window.alert('Not supported by your browser');
done();
return;
}
var fileReader = new FileReader();
fileReader.onload = function(ev) {
context.decodeAudioData(ev.target.result, function(buffer) {
var buf = [];
var data = buffer.getChannelData(0), datum = data[0];
var old = (datum > 0.0), current;
var last = 0, delta, ival;
debug('Sample Count: ' + data.length);
debug('Sample rate: ' + buffer.sampleRate);
for (var idx = 1; idx < data.length; idx++) {
datum = data[idx];
if ((datum > 0.1) || (datum < -0.1)) {
current = (datum > 0.0);
if (current != old) {
delta = idx - last;
if (delta > 2000000) {
delta = 2000000;
}
ival = delta / buffer.sampleRate * 1000;
if (ival >= 0.550 && ival < 0.750) {
ival = 0.650; // Header
} else if (ival >= 0.175 && ival < 0.225) {
ival = 0.200; // sync 1
} else if (ival >= 0.225 && ival < 0.275) {
ival = 0.250; // 0 / sync 2
} else if (ival >= 0.450 && ival < 0.550) {
ival = 0.500; // 1
} else {
// debug(idx + ' ' + buf.length + ' ' + ival);
}
buf.push([parseInt(ival * kHz), current]);
old = current;
last = idx;
}
}
}
io.setTape(buf);
done();
});
};
fileReader.readAsArrayBuffer(file);
}
};
}