1. 伺服器透過 http 連線將連線資料(html 檔案), 送給客戶端
2. 客戶端收到內含 Javascript 可以開啟 WebSocket 連線的 html 檔案
3. 伺服端收到 WebSocket 升級請求, 連線後,依照時間順序,不停將 JPEG (binary)傳給客戶端.
4. 客戶端的 Javascript, 從 WebSocket 收到的 JPEG 資料, 製成 url, 將圖貼至 canvas 就可以了
放在伺服器上的 mjpeg.html 客戶端程式範例:
<html><head><meta charset='UTF-8'></head>
<body><script>
class ViewImageWS {
constructor(width, height) {
this._canvas = document.createElement('canvas');
this._canvas.width = width;
this._canvas.height = height;
this._canvas.style.setProperty('border', '1px solid #000000');
this._context = this._canvas.getContext('2d');
this._height = this._canvas.height;
this._width = this._canvas.width;
document.body.append(this._canvas);
}
set drawImage (_img) {
const scaley = this._height/_img.height;
const scalex = this._width/_img.width;
this._context.save( );
this._context.scale(scalex, scaley);
this._context.drawImage(_img, 0, 0, this._width, this._height);
this._context.restore( );
}
set host(_ip) {
const ws = new WebSocket(`ws://${_ip}`);
ws.onmessage = _jpg => {// jpg binary
const url = URL.createObjectURL(new Blob(
[_jpg.data],
{type: 'image/jpeg'}
));
const img = new Image( );
const release = ( )=> {
URL.revokeObjectURL(url);
img.remove( );
}
img.style= 'transform:rotate(90deg);';// rotate 90 deg if need
img.onerror = release;
img.onload = ( ) => {
this.drawImage = img;
release( );
};
img.src = url;
}
}
};
var viewer = new ViewImageWS(1024, 768);
viewer.host = location.origin.split('//').pop( );
</script></body>
</html>
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