use timer to feed captured bitmap to ffmpeg,to avoid locking of frame

@@ -22,13 +22,32 @@ ipc.on('close-main-window', function () {
 
 var lastRenderTime = 0;
 
+var contentBitmap = null;
+
+var duration = 10000;//set duration 10s
+
+var start = Date.now()
+
 ipc.on('to-main-timer', function () {
-  if (Date.now() - lastRenderTime >= 10000) {
+ /* if(lastMainTimerCalledTime){
+    var now = Date.now();
+    console.log("time-diff:",now - lastMainTimerCalledTime);
+    lastMainTimerCalledTime = now;
+  }
+  else{
+    lastMainTimerCalledTime = Date.now();
+  }
+*/
+  if(contentBitmap && streamIn){
+    streamIn.write(contentBitmap);
+  }
+
+  if (Date.now() - start >= duration) {
     if (streamIn) {
       streamIn.end();
       streamIn = null;
     }
-    if (Date.now() - lastRenderTime >= 15000) {
+    if (Date.now() - start >= duration + 10000) {//quit after duration + 10s
       quit();
     }
   }
@@ -73,17 +92,29 @@ if(!argv.h){//width
   argv.h = "600";
 }
 
+if(!argv.b){//bitrate
+  argv.b = "1000k";
+}
+
+if(!argv.o){//offscreen
+  argv.o = true;
+}
+
 function startFFmpeg(videosize) {
   const args = ['-y','-f', 'rawvideo', '-pix_fmt', 'bgra', '-s' ];
 
   var size = videosize.width + 'x' + videosize.height
 
   args.push(size);
+  args.push('-r');
+  args.push(argv.f);
   args.push.apply( args, ['-i', 'pipe:0'] );
+  args.push('-vf')
+  args.push('fps=fps='+argv.f)
   args.push('-c:v');
   args.push('libx264');
   args.push('-b:v');
-  args.push('1024k');
+  args.push(argv.b);
   args.push('-r:v');
   args.push(argv.f);
    args.push('-an');
@@ -92,8 +123,13 @@ function startFFmpeg(videosize) {
   console.log(args.join` `);
 
   ffmpeg = spawn('ffmpeg', args);
-  ffmpeg.stderr.on('data', chunk => console.log(chunk.toString()));
-  streamIn = duplexer(ffmpeg.stdin, ffmpeg.stdout);
+  if (ffmpeg) {
+    ffmpeg.stderr.on('data', chunk => console.log(chunk.toString()));
+    streamIn = duplexer(ffmpeg.stdin, ffmpeg.stdout);
+  }
+  else {
+    console.log("can't start ffmpeg,please make sure ffmpeg is avaiable");
+  }
 }
 
 app.disableHardwareAcceleration()
@@ -104,22 +140,27 @@ app.once('ready', () => {
     width:argv.w,
     height:argv.h,
     webPreferences: {
-      offscreen: true
+      offscreen: argv.o
     }
   })
   win.loadURL(argv.u)
 
-win.webContents.executeJavaScript('const ipcToMain = require("electron").ipcRenderer;function timerToMain (){ ipcToMain.send("to-main-timer");}setInterval(timerToMain,10000);');
+  var intervalms = 1000 / parseInt(argv.f);
+  
+  var injectScript = 'const ipcToMain = require("electron").ipcRenderer;function timerToMain (){ ipcToMain.send("to-main-timer");}setInterval(timerToMain,' + intervalms + ');';
 
+  win.webContents.executeJavaScript(injectScript);
 
-  var start = Date.now()
-
-  var duration = parseInt(argv.d)*1000
+  duration = parseInt(argv.d)*1000
 
   win.webContents.on("paint", function (event, dirty, image) {
 
     if (!ffmpeg) {
+      start = Date.now();
       startFFmpeg(image.getSize());
+      if(!ffmpeg){
+          sendQuit();
+      }
     }
     lastRenderTime = Date.now();
     var elapsed = lastRenderTime - start
@@ -130,11 +171,12 @@ win.webContents.executeJavaScript('const ipcToMain = require("electron").ipcRend
       }
       console.log("done")
       if(elapsed > duration + 5000){//delay 5s after closingSgit l pipe ,then close
-         win.webContents.executeJavaScript('require("electron").ipcRenderer.send("close-main-window")');
+          sendQuit();
       }
     }
     else {
-      streamIn.write(image.getBitmap());
+     // streamIn.write(image.getBitmap());
+     contentBitmap = image.toBitmap();
     }
 
     //console.log("painting", elapsed, win.webContents.isOffscreen(), win.webContents.getFrameRate())
@@ -142,3 +184,7 @@ win.webContents.executeJavaScript('const ipcToMain = require("electron").ipcRend
   })
   win.webContents.setFrameRate(parseInt(argv.f));
 })
+
+function sendQuit(){
+  win.webContents.executeJavaScript('require("electron").ipcRenderer.send("close-main-window")');
+}