Damian Mehers' Blog Android, VR and Wearables from Geneva, Switzerland.


Android 5.0 Media Browser APIs

When I read the release notes for the Android 5.0 APIs I was delighted to see this:

Android 5.0 introduces the ability for apps to browse the media content library of another app, through the new android.media.browse API.

I set out to try to browse the media in a variety of apps I had installed on my phone.

First I listed the apps that supported the MediaBrowserService:

  private void discoverBrowseableMediaApps(Context context) {
    PackageManager packageManager = context.getPackageManager();
    Intent intent = new Intent(MediaBrowserService.SERVICE_INTERFACE);
    List<ResolveInfo> services = packageManager.queryIntentServices(intent, 0);
    for(ResolveInfo resolveInfo : services) {
      if(resolveInfo.serviceInfo != null && resolveInfo.serviceInfo.applicationInfo != null) {
        ApplicationInfo applicationInfo = resolveInfo.serviceInfo.applicationInfo;
        String label = (String) packageManager.getApplicationLabel(applicationInfo);
        Drawable icon = packageManager.getApplicationIcon(applicationInfo);
        String packageName = resolveInfo.serviceInfo.packageName;
        String className = resolveInfo.serviceInfo.name;
        publishProgress(new AudioApp(label, packageName, className, icon));

The publishProgress method updated the UI and soon I had a list of apps that supported the MediaBrowserService:

Apps that support MediaBrowserService

Next, I wanted to browse the media they exposed using the MediaBrowser classes:

public class BrowseAppMediaActivity extends ListActivity {
  private static final String TAG = “BrowseAppMediaActivity”;
  private final MediaBrowserConnectionListener mMediaBrowserListener =
      new MediaBrowserConnectionListener();
  private MediaBrowser mMediaBrowser;

  public void onCreate(Bundle savedInstanceState) {
    Log.d(TAG, “Connecting to “ + packageName + “ / “ + className);
    ComponentName componentName = new ComponentName(packageName, className);

    Log.d(TAG, “Creating media browser …”);
    mMediaBrowser = new MediaBrowser(this, componentName, mMediaBrowserListener, null);

    Log.d(TAG, “Connecting …”);

  private final class MediaBrowserConnectionListener extends MediaBrowser.ConnectionCallback {
    public void onConnected() {
      Log.d(TAG, “onConnected”);
      String root = mMediaBrowser.getRoot();
      Log.d(TAG, “Have root: “ + root);

    public void onConnectionSuspended() {
      Log.d(TAG, “onConnectionSuspended”);

    public void onConnectionFailed() {
      Log.d(TAG, “onConnectionFailed”);

I’ve cut some code, but assume that the packageName and className are as they were when queried above. No matter what I did, and which app I queried, the onConnectionFailed method was invoked.

Here is the log from when I tried to query the Google Music App:

29195-29195/testapp D/BrowseAppMediaActivity﹕ Connecting to com.google.android.music / com.google.android.music.browse.MediaBrowserService
29195-29195/testapp D/BrowseAppMediaActivity﹕ Creating media browser …
29195-29195/testapp D/BrowseAppMediaActivity﹕ Connecting …
16030-16030/? I/MusicPlaybackService﹕ onStartCommand null / null
16030-16030/? D/MediaBrowserService﹕ Bound to music playback service
16030-16030/? D/MediaBrowserService﹕ onGetRoot fortestapp
16030-16030/? E/MediaBrowserService﹕ package testapp is not signed by Google
16030-16030/? I/MediaBrowserService﹕ No root for client testapp from service android.service.media.MediaBrowserService$ServiceBinder$1
724-819/? I/ActivityManager﹕ Displayed testapp/.BrowseAppMediaActivity: +185ms
29195-29195/testapp E/MediaBrowser﹕ onConnectFailed for ComponentInfo{com.google.android.music/com.google.android.music.browse.MediaBrowserService}
29195-29195/testapp D/BrowseAppMediaActivity﹕ onConnectionFailed

Notice the message about my app not being signed by Google on line 7?

I’m assuming that only authorized apps are allowed to browse Google’s music app such as Google apps supporting Android Wear and Android Auto, but not arbitrary third party apps. Indeed the documentation for people implementing MediaBrowserService.onGetRoot indicates that:

The implementation should verify that the client package has permission to access browse media information before returning the root id; it should return null if the client is not allowed to access this information.

This makes sense, but it is disappointing. Just as users can grant specific apps access to notifications, it would be nice of they could also grant specific apps the right to browser other apps' media.

Please let me know if you discover I am wrong!

Filed under: Android 1 Comment

Using Android Wear to control Google Cardboard Unity VR

Using a VR headset, even one as simple as Google Cardboard, can be mind-blowing.  Nevertheless it is the little things that can also be disconcerting.  For example looking down and seeing you have no arms, despite the fact they still very much feel as though they exist.

I’m convinced that VR experiences are going to transform not just games, but interaction with computers in general, and I’ve been experimenting with some ideas I have about how to create truly useful VR experiences.

As I was working to implement one of my ideas, it occurred to me that I might be able to use the orientation sensors in the Android Wear device I was wearing.  Why not use them as input into the VR experience I was creating?  What if I could bring part of my body from the real world into the VR world?  How about an arm?

I decided to try to find out, and this was the answer:

The experience is nowhere near good enough for games.  But I don’t care about games.  I want to create genuinely useful VR experiences for interacting with computers in general, and I think this is good enough.  I can point to objects, and have them light up.  I can wear smart watches on both wrists (because I really am that cool) and have two arms available in the VR world. 

By tapping and swiping on the wearable screens I can activate in-world functionality, without being taken out of it.  It sure beats sliding a magnet on the side of my face, because it is my arm I am seeing moving in the virtual world.

In the rest of this article I’m going to describe some of technical challenges behind implementing this, how I overcame them, and some of the resources I used on the way.

The tools

This is part of my workspace: Android Studio on the left, Unity on the top-right and MonoDevelop on the bottom-left:

my workspace

I had many reference browser windows open on other screens (obviously), and creating this solution required me being very comfortable in Android, Java and C#.  I’m relatively new to Unity.

Creating a Unity Java Plugin by overriding the Google Cardboard Plugin

The Unity Android Plugin documentation describes how you can create plugins by extending the UnityPlayerActivity Java class, and I experimented with this a little.  I created an Android Library using Android Studio, and implemented my own UnityPlayerActivity derived class.

After a little hassle, I discovered that Unity now supports the “aar” files generated when compiling libraries in Android Studio, although I found the documentation a little out of date on the matter in places.  It was simply a question of copying my generated “aar” file into Unity under Assets|Plugins|Android



When it came to a Google Cardboard Unity project, what I discovered though, is that Google had got there first.  They had created their own UnityPlayerActivity called GoogleUnityActivity.  What I needed to do was override Google’s override:


I included Google’s unity classes as dependencies in my library project:


Once I’d copied the aar file into the Unity Android Plugins folder and ran the test app, I was delighted to see my activity say “Cooey” in the log.


Receiving the watch’s orientation to the phone

The next step was to receive Android Wear Messages from Android Wear on the watch, containing orientation messages.

I recreated my project, this time including support for Android Wear:


I made the Unity activity I’d created do a little more than say “Cooey”. 

First I used the Capabilities mechanism to tell other Android Wear devices that this device (the phone) was interested in arm orientation messages:


… and I set it up to receive Android Wear messages and pass them over to Unity using UnitySendMessage:


Sending the watch’s orientation to the phone

This was simply a question of looking out for Android Wear nodes that supported the right capability, listening for orientation sensor changes, and sending Android Wear messages to the right node.  This is the watch code:


I did discover that some wearables don’t support the required sensors, although I imagine more modern ones will.

Using the watch’s orientation to animate a block on the screen

Inside Unity I created a cube which tweaked into a rectangle, and made it a child of the CardboardMain’s camera, so that it moved when I moved:


See the “Script” field on the bottom right-hand side?  I have a script called “WristController” that is attached to the “wrist” (white blob).  This is where I receive orientation messages sent from the watch, via the UnityPlayerActivity derived Java class I’d created.

I started off simply assigning the received orientation to the block’s orientation by assigning to transform.eulerAngles


This worked, but was super-jerky.  I went searching and discovered Lerps and Slerps for smoothly moving from one rotation to another.  My updated code:


Animating an arm instead of a block

I was pleased to be smoothly animating a block, but my arm doesn’t quite look like that.  It is more armish.  I went looking for a model of an arm that I could import and use instead.  I found a YouTube Unity video called ADDING ARMS by Asbjørn Thirslund, in which he explains how to to import and use a free arms model by eafg.

It was simply a question of sizing and positioning the arms properly as a child of the Cardboard main camera, and then adding the script I’d used to animate the block.

I also removed the right-hand arm, since it looked a little weird to have a zombie arm doing nothing.


The ArmController script you see in this screen capture has the same contents as the WristController I’d used to move the block.

Final Thoughts

There is enough of a lag to make this technique impractical for games, but not enough to make it impractical for the kinds of non-game experiences I have in mind. 

I’d also need to add calibration, since the watch may be pointing in any direction initially – if I assume it always starts straight out, that would be good enough.  Detecting where the arm is pointing shouldn’t be too hard, since the cardboard code already does gaze detection – so many possibilities, but so little time for side-projects such as this!

This has been a fun interlude on my way to creating what I hope to be a genuinely useful VR experience based around browsing books your friends have read … more on that later.