use ffmpeg to record video ok,need more improvement

+'use strict';
+
 const {app, BrowserWindow} = require('electron');
+const ipc = require('electron').ipcMain;
+const duplexer = require('duplexer3');
+const {spawn} = require('child_process');
+
+var streamIn =  null;
+var ffmpeg = null;
+
+function quit(){
+  if(streamIn){
+    streamIn.end();
+    streamIn = null;
+  }
+  app.quit();
+}
+
+ipc.on('close-main-window', function () {
+    quit();
+});
+
+var lastRenderTime = 0;
+
+ipc.on('to-main-timer', function () {
+   if(Date.now() - lastRenderTime >= 10000){
+      quit();
+   }
+});
 
 var subarg = require('subarg');
 
@@ -17,11 +45,43 @@ if (argv.d) {
   console.log(args);
 }
 
-if(!argv.u){
+if(!argv.u){//url
   console.log("you must input the web url to record with : -u ");
   return app.quit();
 }
 
+if(!argv.d){//duration
+  console.log("you must set the record duration in seconds with : -d ");
+  return app.quit();
+}
+
+if(!argv.f){//framerate
+  argv.f = "20";
+}
+
+function startFFmpeg(videosize) {
+  const args = ['-y','-f', 'rawvideo', '-pix_fmt', 'bgra', '-s' ];
+
+  var size = videosize.width + 'x' + videosize.height
+
+  args.push(size);
+  args.push.apply( args, ['-i', 'pipe:0'] );
+  args.push('-c:v');
+  args.push('libx264');
+  args.push('-b:v');
+  args.push('1024k');
+  args.push('-r:v');
+  args.push(argv.f);
+   args.push('-an');
+  args.push(argv._[0]);
+
+  console.log(args.join` `);
+
+  ffmpeg = spawn('ffmpeg', args);
+  ffmpeg.stderr.on('data', chunk => console.log(chunk.toString()));
+  streamIn = duplexer(ffmpeg.stdin, ffmpeg.stdout);
+}
+
 app.disableHardwareAcceleration()
 
 let win
@@ -33,17 +93,34 @@ app.once('ready', () => {
   })
   win.loadURL(argv.u)
 
-  var now = Date.now()
+win.webContents.executeJavaScript('const ipcToMain = require("electron").ipcRenderer;function timerToMain (){ ipcToMain.send("to-main-timer");}setInterval(timerToMain,10000);');
+
+
+  var start = Date.now()
+
+  var duration = parseInt(argv.d)*1000
+
+  win.webContents.on("paint", function (event, dirty, image) {
+
+    if (!ffmpeg) {
+      startFFmpeg(image.getSize());
+    }
+    lastRenderTime = Date.now();
+    var elapsed = lastRenderTime - start
+    if (elapsed > duration) {
+      if (streamIn) {
+        streamIn.end();
+        streamIn = null;
+      }
+      console.log("done")
+      win.webContents.executeJavaScript('require("electron").ipcRenderer.send("close-main-window")');
+    }
+    else {
+      streamIn.write(image.getBitmap());
+    }
 
-  win.webContents.on("paint", function(event, dirty, image){
-  console.log(
-    "painting", 
-    Date.now() - now, 
-    win.webContents.isOffscreen(), 
-    win.webContents.getFrameRate()
-  )
+    //console.log("painting", elapsed, win.webContents.isOffscreen(), win.webContents.getFrameRate())
 
-  now = Date.now()
   })
-  win.webContents.setFrameRate(20)
+  win.webContents.setFrameRate(parseInt(argv.f));
 })

@@ -14,6 +14,8 @@
   "author": "hubin",
   "license": "MIT",
   "dependencies": {
+    "child_process": "^1.0.2",
+    "duplexer3": "^0.1.4",
     "electron": "^1.6.11",
     "subarg": "^1.0.0"
   },