mp4 play issue for varnish4,1

[matrix]

Hi I am facing problem about mp4 play.

I already set the stream with  true.

  if (bereq.url ~ "^[^?]*\.(mp3|mp4)(\?.*)?$") {
    set beresp.do_stream = true;
}

File download is OK, but mp4 does not play immediately using chrome or Firefox.

Does anyone have any solutions?

(ex: Does Pipe during streaming.

Best regards.