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MIT License
Copyright (c) 2023 Christian Kegel
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@picocss/pico@1/css/pico.min.css">
<link rel="stylesheet" href="./style.css">
<title>Web-SSTV</title>
</head>
<body>
<main class="container">
<h1>Web SSTV</h1>
<h3>Send SSTV signals from your browser</h3>
<select id="modeSelect">
<option value="none" selected disabled hidden>Select a mode</option>
<option value="M1">Martin M1</option>
<option value="M2">Martin M2</option>
<option value="S1">Scottie 1</option>
<option value="S2">Scottie 2</option>
<option value="SDX">Scottie DX</option>
</select>
<label id="imgLabel" for="imgPicker">Select an Image</label>
<input type="file" name="imgPicker" id="imgPicker"/>
<center id="imgArea" class="container">
<canvas id="imgCanvas" width="320" height="256"></canvas>
<br>
<span id="warningText"></span>
</center>
<button id="startButton" class="contrast" disabled>Encode</button>
</main>
<footer class="container">
<p>Currently supports encoding (sending) in Martin and Scottie formats. SSTV signal decoding and more encoding modes coming soon.</p>
<p>&copy 2023 Christian Kegel - Available under the MIT License</p>
</footer>
</body>
<script src="./script.js"></script>
</html>

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/*
MIT License
Copyright (c) 2023 Christian Kegel
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
*/
//---------- Encoding Constants ----------//
const PREFIX_PULSE_LENGTH = 0.1; //100 ms
const HEADER_PULSE_LENGTH = 0.3; //300 ms
const HEADER_BREAK_LENGTH = 0.01; //10 ms
const VIS_BIT_LENGTH = 0.03; //30 ms
const SYNC_PULSE_FREQ = 1200;
const BLANKING_PULSE_FREQ = 1500;
const VIS_BIT_FREQ = {
ONE: 1100,
ZERO: 1300,
};
class Format {
#numScanLines;
#vertResolution;
#blankingInterval;
#scanLineLength;
#syncPulseLength;
#VISCode;
#preparedImage = [];
constructor(numScanLines, vertResolution, blankingInterval, scanLineLength, syncPulseLength, VISCode) {
this.#numScanLines = numScanLines;
this.#vertResolution = vertResolution;
this.#blankingInterval = blankingInterval;
this.#scanLineLength = scanLineLength;
this.#syncPulseLength = syncPulseLength;
this.#VISCode = VISCode;
}
getRGBValueAsFreq(data, scanLine, vertPos) {
const index = scanLine * (this.#vertResolution * 4) + vertPos * 4;
let red = data[index] * 3.137 + 1500;
let green = data[index + 1] * 3.137 + 1500;
let blue = data[index + 2] * 3.137 + 1500;
return [red, green, blue];
}
encodePrefix(oscillator, startTime) {
let time = startTime;
oscillator.frequency.setValueAtTime(1900, time);
time += PREFIX_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(1500, time);
time += PREFIX_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(1900, time);
time += PREFIX_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(1500, time);
time += PREFIX_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(2300, time);
time += PREFIX_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(1500, time);
time += PREFIX_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(2300, time);
time += PREFIX_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(1500, time);
time += PREFIX_PULSE_LENGTH;
return time;
}
encodeHeader(oscillator, startTime) {
let time = startTime;
//----- Format Header -----//
oscillator.frequency.setValueAtTime(1900, time);
time += HEADER_PULSE_LENGTH;
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += HEADER_BREAK_LENGTH;
oscillator.frequency.setValueAtTime(1900, time);
time += HEADER_PULSE_LENGTH;
//-----VIS Code-----//
//--- Start Bit ---//
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += VIS_BIT_LENGTH;
//--- 7 Bit Format Code ---//
let parity = 0;
let bitFreq;
this.#VISCode.reverse().forEach((bit) => {
if(bit){
bitFreq = VIS_BIT_FREQ.ONE;
++parity;
}
else
bitFreq = VIS_BIT_FREQ.ZERO;
oscillator.frequency.setValueAtTime(bitFreq, time)
time += VIS_BIT_LENGTH;
});
//--- Even Parity Bit ---//
bitFreq = parity % 2 == 0 ? VIS_BIT_FREQ.ZERO : VIS_BIT_FREQ.ONE;
oscillator.frequency.setValueAtTime(bitFreq, time)
time += VIS_BIT_LENGTH;
//--- End Bit ---//
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += VIS_BIT_LENGTH;
return time;
}
prepareImage(data) {
this.#preparedImage = data;
}
encodeSSTV(oscillator, startTime) {
throw new Error("Must be defined by a subclass");
}
get numScanLines() {
return this.#numScanLines;
}
get vertResolution() {
return this.#vertResolution;
}
get blankingInterval() {
return this.#blankingInterval;
}
get scanLineLength() {
return this.#scanLineLength;
}
get syncPulseLength() {
return this.#syncPulseLength;
}
get VISCode() {
return this.#VISCode;
}
get preparedImage(){
return this.#preparedImage;
}
}
//---------- Format Encode Implementation ----------//
class MartinMOne extends Format {
constructor() {
let numScanLines = 256;
let vertResolution = 320;
let blankingInterval = 0.000572;
let scanLineLength = 0.146432;
let syncPulseLength = 0.004862;
let VISCode = [false, true, false, true, true, false, false];
super(numScanLines, vertResolution, blankingInterval, scanLineLength, syncPulseLength, VISCode);
}
prepareImage(data) {
let preparedImage = [];
for(let scanLine = 0; scanLine < this.numScanLines; ++scanLine){
let red = [];
let green = [];
let blue = [];
for(let vertPos = 0; vertPos < this.vertResolution; ++vertPos){
let freqs = this.getRGBValueAsFreq(data, scanLine, vertPos);
red.push(freqs[0]);
green.push(freqs[1]);
blue.push(freqs[2]);
}
preparedImage.push([green, blue, red]);
}
super.prepareImage(preparedImage);
}
encodeSSTV(oscillator, startTime) {
let time = startTime;
time = super.encodePrefix(oscillator, time);
time = super.encodeHeader(oscillator, time);
for(let scanLine = 0; scanLine < super.numScanLines; ++scanLine){
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
oscillator.frequency.setValueAtTime(BLANKING_PULSE_FREQ, time);
time += super.blankingInterval;
for(let dataLine = 0; dataLine < 3; ++dataLine) {
oscillator.frequency.setValueCurveAtTime(super.preparedImage[scanLine][dataLine], time, super.scanLineLength);
time += super.scanLineLength;
oscillator.frequency.setValueAtTime(BLANKING_PULSE_FREQ, time);
time += super.blankingInterval;
}
}
oscillator.start(startTime);
oscillator.stop(time);
}
}
class MartinMTwo extends Format {
constructor() {
let numScanLines = 256;
let vertResolution = 320;
let blankingInterval = 0.000572;
let scanLineLength = 0.073216;
let syncPulseLength = 0.004862;
let VISCode = [false, true, false, true, false, false, false];
super(numScanLines, vertResolution, blankingInterval, scanLineLength, syncPulseLength, VISCode);
}
prepareImage(data) {
let preparedImage = [];
for(let scanLine = 0; scanLine < this.numScanLines; ++scanLine){
let red = [];
let green = [];
let blue = [];
for(let vertPos = 0; vertPos < this.vertResolution; ++vertPos){
let freqs = this.getRGBValueAsFreq(data, scanLine, vertPos);
red.push(freqs[0]);
green.push(freqs[1]);
blue.push(freqs[2]);
}
preparedImage.push([green, blue, red]);
}
super.prepareImage(preparedImage);
}
encodeSSTV(oscillator, startTime) {
let time = startTime;
time = super.encodePrefix(oscillator, time);
time = super.encodeHeader(oscillator, time);
for(let scanLine = 0; scanLine < super.numScanLines; ++scanLine){
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
oscillator.frequency.setValueAtTime(BLANKING_PULSE_FREQ, time);
time += super.blankingInterval;
for(let dataLine = 0; dataLine < 3; ++dataLine) {
oscillator.frequency.setValueCurveAtTime(super.preparedImage[scanLine][dataLine], time, super.scanLineLength);
time += super.scanLineLength;
oscillator.frequency.setValueAtTime(BLANKING_PULSE_FREQ, time);
time += super.blankingInterval;
}
}
oscillator.start(startTime);
oscillator.stop(time);
}
}
class ScottieOne extends Format {
constructor() {
let numScanLines = 256;
let vertResolution = 320;
let blankingInterval = 0.0015;
let scanLineLength = 0.138240;
let syncPulseLength = 0.009;
let VISCode = [false, true, true, true, true, false, false];
super(numScanLines, vertResolution, blankingInterval, scanLineLength, syncPulseLength, VISCode);
}
prepareImage(data) {
let preparedImage = [];
for(let scanLine = 0; scanLine < this.numScanLines; ++scanLine){
let red = [];
let green = [];
let blue = [];
for(let vertPos = 0; vertPos < this.vertResolution; ++vertPos){
let freqs = this.getRGBValueAsFreq(data, scanLine, vertPos);
red.push(freqs[0]);
green.push(freqs[1]);
blue.push(freqs[2]);
}
preparedImage.push([green, blue, red]);
}
super.prepareImage(preparedImage);
}
encodeSSTV(oscillator, startTime) {
let time = startTime;
time = super.encodePrefix(oscillator, time);
time = super.encodeHeader(oscillator, time);
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
for(let scanLine = 0; scanLine < super.numScanLines; ++scanLine){
for(let dataLine = 0; dataLine < 3; ++dataLine) {
if(dataLine == 2){
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
}
oscillator.frequency.setValueAtTime(BLANKING_PULSE_FREQ, time);
time += super.blankingInterval;
oscillator.frequency.setValueCurveAtTime(super.preparedImage[scanLine][dataLine], time, super.scanLineLength);
time += super.scanLineLength;
}
}
oscillator.start(startTime);
oscillator.stop(time);
}
}
class ScottieTwo extends Format {
constructor() {
let numScanLines = 256;
let vertResolution = 320;
let blankingInterval = 0.0015;
let scanLineLength = 0.088064;
let syncPulseLength = 0.009;
let VISCode = [false, true, true, true, false, false, false];
super(numScanLines, vertResolution, blankingInterval, scanLineLength, syncPulseLength, VISCode);
}
prepareImage(data) {
let preparedImage = [];
for(let scanLine = 0; scanLine < this.numScanLines; ++scanLine){
let red = [];
let green = [];
let blue = [];
for(let vertPos = 0; vertPos < this.vertResolution; ++vertPos){
let freqs = this.getRGBValueAsFreq(data, scanLine, vertPos);
red.push(freqs[0]);
green.push(freqs[1]);
blue.push(freqs[2]);
}
preparedImage.push([green, blue, red]);
}
super.prepareImage(preparedImage);
}
encodeSSTV(oscillator, startTime) {
let time = startTime;
time = super.encodePrefix(oscillator, time);
time = super.encodeHeader(oscillator, time);
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
for(let scanLine = 0; scanLine < super.numScanLines; ++scanLine){
for(let dataLine = 0; dataLine < 3; ++dataLine) {
if(dataLine == 2){
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
}
oscillator.frequency.setValueAtTime(BLANKING_PULSE_FREQ, time);
time += super.blankingInterval;
oscillator.frequency.setValueCurveAtTime(super.preparedImage[scanLine][dataLine], time, super.scanLineLength);
time += super.scanLineLength;
}
}
oscillator.start(startTime);
oscillator.stop(time);
}
}
class ScottieDX extends Format {
constructor() {
let numScanLines = 256;
let vertResolution = 320;
let blankingInterval = 0.0015;
let scanLineLength = 0.3456;
let syncPulseLength = 0.009;
let VISCode = [true, false, false, true, true, false, false];
super(numScanLines, vertResolution, blankingInterval, scanLineLength, syncPulseLength, VISCode);
}
prepareImage(data) {
let preparedImage = [];
for(let scanLine = 0; scanLine < this.numScanLines; ++scanLine){
let red = [];
let green = [];
let blue = [];
for(let vertPos = 0; vertPos < this.vertResolution; ++vertPos){
let freqs = this.getRGBValueAsFreq(data, scanLine, vertPos);
red.push(freqs[0]);
green.push(freqs[1]);
blue.push(freqs[2]);
}
preparedImage.push([green, blue, red]);
}
super.prepareImage(preparedImage);
}
encodeSSTV(oscillator, startTime) {
let time = startTime;
time = super.encodePrefix(oscillator, time);
time = super.encodeHeader(oscillator, time);
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
for(let scanLine = 0; scanLine < super.numScanLines; ++scanLine){
for(let dataLine = 0; dataLine < 3; ++dataLine) {
if(dataLine == 2){
oscillator.frequency.setValueAtTime(SYNC_PULSE_FREQ, time);
time += super.syncPulseLength;
}
oscillator.frequency.setValueAtTime(BLANKING_PULSE_FREQ, time);
time += super.blankingInterval;
oscillator.frequency.setValueCurveAtTime(super.preparedImage[scanLine][dataLine], time, super.scanLineLength);
time += super.scanLineLength;
}
}
oscillator.start(startTime);
oscillator.stop(time);
}
}
//---------- Frontend Controls ----------//
const audioCtx = new AudioContext();
let imageLoaded = false;
let modeSelect = document.getElementById("modeSelect")
let startButton = document.getElementById("startButton");
let imgPicker = document.getElementById("imgPicker");
let warningText = document.getElementById("warningText");
let canvas = document.getElementById("imgCanvas");
let canvasCtx = canvas.getContext("2d");
imgPicker.addEventListener("change", (e) => {
var reader = new FileReader();
reader.onload = function(event){
var img = new Image();
img.onload = function(){
canvas.width = 320;
canvas.height = 256;
canvasCtx.drawImage(img,0,0, canvas.width, canvas.height);
}
img.src = event.target.result;
if(modeSelect.value != "none"){
warningText.textContent = "";
startButton.disabled = false;
imageLoaded = true;
}
}
reader.readAsDataURL(e.target.files[0]);
});
modeSelect.addEventListener("change", (e) => {
if(modeSelect.value != "none"){
warningText.textContent = "";
startButton.disabled = !imageLoaded;
}
});
startButton.onclick = () => {
let format;
if(modeSelect.value == "M1")
format = new MartinMOne();
else if(modeSelect.value == "M2")
format = new MartinMTwo();
else if(modeSelect.value == "S1")
format = new ScottieOne();
else if(modeSelect.value == "S2")
format = new ScottieTwo();
else if(modeSelect.value == "SDX")
format = new ScottieDX();
else {
warningText.textContent = "You must select a mode";
startButton.disabled = true;
return;
}
if(!imageLoaded){
warningText.textContent = "You must upload an image";
startButton.disabled = true;
return;
}
let canvasData = canvasCtx.getImageData(0, 0, canvas.width, canvas.height);
warningText.textContent = "";
if (audioCtx.state === "suspended") {
audioCtx.resume();
}
let oscillator = audioCtx.createOscillator();
oscillator.type = "sine";
oscillator.connect(audioCtx.destination);
format.prepareImage(canvasData.data);
format.encodeSSTV(oscillator, audioCtx.currentTime + 1);
};

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#imgCanvas {
padding: 5px;
}
#imgArea {
padding: 10px;
color: red;
}