Renderer volume can be changed with volume keys.

src/com/github/nutomic/controldlna/MainActivity.java

@@ -10,6 +10,7 @@ import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentPagerAdapter;
 import android.support.v4.app.FragmentTransaction;
 import android.support.v4.view.ViewPager;
+import android.view.KeyEvent;
 
 import com.actionbarsherlock.app.ActionBar;
 import com.actionbarsherlock.app.SherlockFragmentActivity;
@@ -144,5 +145,25 @@ public class MainActivity extends SherlockFragmentActivity implements
 		getSupportActionBar().selectTab(getSupportActionBar().getTabAt(0));
 		mRendererFragment.setPlaylist(playlist, start);
 	}
+	
+	/**
+	 * Sends volume key events to RendererFragment (which sends them to 
+	 * media renderer).
+	 */
+	@Override
+	public boolean dispatchKeyEvent(KeyEvent event) {		
+        switch (event.getKeyCode()) {
+        case KeyEvent.KEYCODE_VOLUME_UP:
+            if (event.getAction() == KeyEvent.ACTION_DOWN)
+                mRendererFragment.changeVolume(true);
+            return true;
+        case KeyEvent.KEYCODE_VOLUME_DOWN:
+            if (event.getAction() == KeyEvent.ACTION_DOWN)
+                mRendererFragment.changeVolume(false);
+            return true;
+        default:
+            return super.dispatchKeyEvent(event);
+        }
+    }
 
 }

src/com/github/nutomic/controldlna/RendererFragment.java

@@ -28,6 +28,8 @@ import org.teleal.cling.support.model.DIDLContent;
 import org.teleal.cling.support.model.PositionInfo;
 import org.teleal.cling.support.model.SeekMode;
 import org.teleal.cling.support.model.item.Item;
+import org.teleal.cling.support.renderingcontrol.callback.GetVolume;
+import org.teleal.cling.support.renderingcontrol.callback.SetVolume;
 
 import android.app.AlertDialog;
 import android.content.ComponentName;
@@ -484,4 +486,40 @@ public class RendererFragment extends Fragment implements
 	public void onStopTrackingTouch(SeekBar seekBar) {
 	}
 
+	/**
+	 * Increases or decreases volume.
+	 * 
+	 * @param increase True to increase volume, false to decrease.
+	 */
+	@SuppressWarnings("rawtypes")
+	public void changeVolume(final boolean increase) {
+		if (mCurrentRenderer == null)
+			return;
+    	final Service<?, ?> service = mCurrentRenderer.findService(
+    			new ServiceType("schemas-upnp-org", "RenderingControl"));
+    	mUpnpService.getControlPoint().execute(new GetVolume(service) {
+			
+			@Override
+			public void failure(ActionInvocation invocation, 
+					UpnpResponse operation, String defaultMessage) {
+				Log.d(TAG, "Failed to get current Volume: " + defaultMessage);
+			}
+			
+			@Override
+			public void received(ActionInvocation invocation, int volume) {
+				int newVolume = volume + ((increase) ? 4 : -4);
+				if (newVolume < 0) newVolume = 0;
+				mUpnpService.getControlPoint().execute(new SetVolume(service, 
+						newVolume) {
+					
+					@Override
+					public void failure(ActionInvocation invocation, 
+							UpnpResponse operation, String defaultMessage) {
+						Log.d(TAG, "Failed to set new Volume: " + defaultMessage);
+					}
+				});
+			}
+		});	
+	}
+
 }