Can't get speech recognition result from Google API?

Question

I started to us https://cloud.google.com/speech/ and the test demo worked for me but when I tried with my own files it doesn't seem to work.

I tried with https://speech.googleapis.com/v1beta1/speech:syncrecognize

{
      "config": {
          "encoding":"LINEAR16",
          "sample_rate": 16000
        },
      "audio": {
        "uri":"gs://test-speech-recognition/arth_the_rat.mp3"
      }
}

getting {}

Also tried with async getting

{
  "name": "7572699807343070889",
  "metadata": {
    "@type": "type.googleapis.com/google.cloud.speech.v1beta1.AsyncRecognizeMetadata",
    "progressPercent": 100,
    "startTime": "2016-09-10T21:15:59.019595Z",
    "lastUpdateTime": "2016-09-10T21:16:07.687943Z"
  },
  "done": true,
  "response": {
    "@type": "type.googleapis.com/google.cloud.speech.v1beta1.AsyncRecognizeResponse"
  }
}

What am I doing wrong ?