Allows changing the cameras

When testing selecting different cameras online, a problem with the device
handle was found: after closing the stream, we can successfully reopen it
but never get frames. This commit works around that issue.

uvcengine/uvccameracontrol.cpp

@@ -34,6 +34,8 @@ void UVCCameraControl::setState(QCamera::State state)
         case QCamera::LoadedState:
             if (m_state == QCamera::UnloadedState && !(succeeded=m_session->load()))
                 return;
+            if (m_state == QCamera::ActiveState)
+                succeeded = m_session->stopPreview();
             break;
 
         case QCamera::ActiveState:

uvcengine/uvccamerasession.cpp

@@ -93,9 +93,10 @@ bool UVCCameraSession::unload()
     if (streaming)
         stopPreview();
 
-    if (devh)
-        uvc_close(devh);
-    devh = NULL;
+    // TODO: closing here seems to mess up the device
+    //if (devh)
+    //    uvc_close(devh);
+    //devh = NULL;
 
     m_supportedViewfinderSettings.clear();
     return true;
@@ -127,7 +128,7 @@ bool UVCCameraSession::startPreview()
         return false;
     }
 
-    res = uvc_stream_start(strmh, cb, (void*) this, 2.0f, 0);
+    res = uvc_stream_start(strmh, cb, (void*) this, 1.5f, 0);
     if (res != UVC_SUCCESS) {
         qDebug() << "uvc_stream_start" << uvc_strerror(res);
         return false;
@@ -203,6 +204,7 @@ bool UVCCameraSession::stopPreview()
             break;
     if (res != UVC_SUCCESS && res != UVC_ERROR_INVALID_PARAM)
         qDebug() << "uvc_stream_stop" << uvc_strerror(res);
+    uvc_stream_close(strmh);
 
     streaming = false;
     frameReference.invalidate();

uvcengine/uvcserviceplugin.cpp

@@ -9,7 +9,7 @@ QMediaService* UVCServicePlugin::create(const QString &key)
 
 void UVCServicePlugin::release(QMediaService *service)
 {
-    qDebug() << "Plugin release";
+    delete service;
 }
 
 QByteArray UVCServicePlugin::defaultDevice(const QByteArray &service) const