MediaPlayer on iOS, no sound

A very basic app which streams video from vine does not produce any sound on iOS devices. The same source code works ok on Android.

import QtQuick 2.2
import QtQuick.Controls 1.1
import QtMultimedia 5.0

ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("Hello World")

menuBar: MenuBar {
Menu {
title: qsTr("File")
MenuItem

{ text: qsTr("Exit") onTriggered: Qt.quit(); }

}
}

Video

{ source: "https://v.cdn.vine.co/r/videos/5872443F831066199665323933696_16e5e0daf03.3.2.mp4?versionId=f1DLKE9EyyuC3VscFefCcP_4kn7jGRub" anchors.fill: parent autoPlay: true volume: 1.0 }

}