write EPIPE

I have got 

> write EPIPE WriteWrap.afterWrite

I don't know why and how to solve this. this is my parameter:

```
let avconv_params = [
    "-i","pipe:0",
    "-r","25",
    "-ss","1",
    "-frames:v","1",
    "-f","image2",
    "pipe:1",
  ]
```