application development - No video shown in Ubuntu Touch QML app video player

I'm trying to play a video in an Ubuntu Touch QML app. The audio plays, but no video is shown.

A minimalistic version:

import QtQuick 2.4
import Ubuntu.Components 1.2
import QtMultimedia 5.5

MainView {

    applicationName: "untitled.username"
    Video {
        anchors.fill: parent
        source: "http://feeds.nos.nl/~r/journaal20uur/~3/JRJKV6kpvRc/mp4_web03.mp4"
        autoPlay: true
    }
}

This works as expected when deploying on the desktop (i.e. video is shown). But on a BQ Aquaris 10 tablet only the audio is played, but no video is shown. I've tried to play a WebM, and local stored file too, but same results.

The app has AppArmor's networking and video Security Policy Group set. I'm using framework ubuntu-sdk-15.04.5. My device is on the current OTA11 rc. Anything else I can try?