+void Mixer::wait_for_next_frame()
+{
+ unique_lock<mutex> lock(frame_num_mutex);
+ unsigned old_frame_num = frame_num;
+ frame_num_updated.wait_for(lock, seconds(1), // Timeout is just in case.
+ [old_frame_num, this]{ return this->frame_num > old_frame_num; });
+}
+