DeviceProvider.start

Starts providering the devices. This will cause #GST_MESSAGE_DEVICE_ADDED and #GST_MESSAGE_DEVICE_REMOVED messages to be posted on the provider's bus when devices are added or removed from the system.

Since the #GstDeviceProvider is a singleton, gst.device_provider.DeviceProvider.start may already have been called by another user of the object, gst.device_provider.DeviceProvider.stop needs to be called the same number of times.

After this function has been called, gst.device_provider.DeviceProvider.getDevices will return the same objects that have been received from the #GST_MESSAGE_DEVICE_ADDED messages and will no longer probe.