support record audio using input device virtual-audio-capturer

 webpage_recorder：利用elecron离屏渲染网页，把抓取的页面图像通过pipe传递给ffmpeg，利用ffmpeg编码成视频
-环境要求:npm, electron，ffmpeg
+环境要求:npm, electron，ffmpeg，virtual-video-capturer(可以从https://sourceforge.net/projects/virtualaudiodev/files/下载)
 
 安装:
 npm install 
 
 运行命令示例：
 ;record duration 30s framerate 20fps width 640 height 320 videobitrate 800k
-electron . -u http://182.92.9.182:9090/media/hlsPlayer/hlsPlayer.html -d 30 -f 20 -w 640 -h 320 -b 800k test.mp4
+electron . -u http://182.92.9.182:9090/media/hlsPlayer/hlsPlayer.html -d 30 -f 20 -w 640 -h 320 -b 800k test.flv
+ffmpeg -i test.flv -acodec copy -vcodec copy test.mp4
 
 局限：
 1. electron需要在桌面环境下运行
 2. 捕获视频间隔不够均匀
-3. 还不能捕获声音

@@ -109,6 +109,12 @@ function startFFmpeg(videosize) {
   args.push('-r');
   args.push(argv.f);
   args.push.apply( args, ['-i', 'pipe:0'] );
+   // /*
+  args.push('-f');
+  args.push('dshow');
+  args.push('-i');
+  args.push('audio=virtual-audio-capturer');
+  //*/
   args.push('-vf')
   args.push('fps=fps='+argv.f)
   args.push('-c:v');
@@ -117,7 +123,9 @@ function startFFmpeg(videosize) {
   args.push(argv.b);
   args.push('-r:v');
   args.push(argv.f);
-   args.push('-an');
+
+  args.push('-acodec');
+  args.push('aac');
   args.push(argv._[0]);
 
   console.log(args.join` `);

 ;record duration 30s framerate 20fps width 640 height 320 videobitrate 800k
-electron . -u http://182.92.9.182:9090/media/hlsPlayer/hlsPlayer.html -d 30 -f 20 -w 640 -h 320 -b 800k test.mp4
+electron . -u http://182.92.9.182:9090/media/hlsPlayer/hlsPlayer.html -d 30 -f 20 -w 640 -h 320 -b 800k test.flv
+ffmpeg -i test.flv -vcodec copy -acodec copy test.mp4