why is it that the recorded remote is fast forward

[huhaibing]

Here's what I did.
first in onaddstream, I creat recoder Object by "recorder = new RecordRTC(e.stream,{type:'video'});"
then I set a timer to record video every fixed time . when time is voer ,i record video by "recorder.stopRecording(postFiles);
recorder.clearRecordedData();
recorder.startRecording();
"

finally, i use the player to play the video ,i found it is so quick.it looks like it's accelerating.

what's wrong with me ,Thank you very much