If a new media stream is added to a presentation (e.g., during a live presentation), the whole presentation description should be sent again, rather than just the additional components, so that components can be deleted.
如果新的媒体流被添加到演示文稿中（例如，在实时演示中），则应该再次发送整个演示文稿描述，而不仅仅是附加的组件，以便可以删除组件。