add -shortest option when call ffmpeg to let it write the end of mp4 when pipe closed

@@ -6,8 +6,7 @@ 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.flv
-ffmpeg -i test.flv -acodec copy -vcodec copy 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.mp4
 
 局限：
 1. electron需要在桌面环境下运行

@@ -126,6 +126,7 @@ function startFFmpeg(videosize) {
 
   args.push('-acodec');
   args.push('aac');
+  args.push('-shortest');
   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.flv
-ffmpeg -i test.flv -vcodec copy -acodec copy 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.mp4