私有的方法

 public void cascadeSetVideoSelection(
            final VideoSelectionParam videoSelectionParams,
            final CascadeTopoTree cascadeTopoTree,
            final CascadeConference cascadeConference)
    {
        if (logger.isDebugEnabled())
        {
            logger.debug("begin to cascadeSetVideoSelection.");
        }
        
        VideoSelectionParam videoParam = new VideoSelectionParam();
        //获取DstScreen ParticipantID和SrcScreen ParticipantID
        videoParam.getParticipantId(videoSelectionParams);
        
        //DstScreenPartID 
        ParticipantID dstScreenParticipantId = videoParam.getCascadeDstScreen();
        if (null == dstScreenParticipantId)
        {
            logger.warn("get dstScreenParticipantId is null.");
            return;
        }
        
        //SrcScreenPartID
        ParticipantID srcScreenParticipantId = videoParam.getCascadeSrcScreen();
        if (null == srcScreenParticipantId)
        {
            logger.warn("get srcScreenParticipantId is null.");
            return;
        }
        
        //得到DstScreen的会议ID
        String dstScreenConferID = getDstScreenConferenID(dstScreenParticipantId);
        if (null == dstScreenConferID)
        {
            logger.warn("get dstScreenConferID is null.");
            return;
        }
        
        //SrcScreen会议ID
        String srcScreenConferenceID = getSrcScreenConferenID(srcScreenParticipantId);
        if (null == srcScreenConferenceID)
        {
            logger.warn("get srcScreenConferenceID is null.");
            return;
        }
        
        //DstScreen选看上级
        boolean srcScreenIsParent = isParentByConferenID(dstScreenConferID,
                srcScreenConferenceID, cascadeTopoTree);
        
        //DstScreen选看下级
        boolean dstScreenIsParent = isParentByConferenID(srcScreenConferenceID,
                dstScreenConferID, cascadeTopoTree);
        
        //同一个MCU选看
        if (dstScreenConferID.equals(srcScreenConferenceID))
        {
            sendSameOneVideoSelection(dstScreenConferID, videoSelectionParams);
        }
        
        //SrcScreen是DstScreen的上级
        if (srcScreenIsParent)
        {
            sendSouthVideoSelection(cascadeTopoTree, cascadeConference,
                    dstScreenConferID, srcScreenConferenceID, videoParam);
        }
        
        //DstScreen是SrcScreen的上级
        else if (dstScreenIsParent)
        {
            sendNorthVideoSelection(cascadeTopoTree, cascadeConference,
                    dstScreenConferID, srcScreenConferenceID, videoParam);
        }
        
        //左右选看
        else
        {
            sendRelatingVideoSelection(cascadeConference, cascadeTopoTree,
                    dstScreenConferID, srcScreenConferenceID, videoParam);
        }
        
        if (logger.isDebugEnabled())
        {
            logger.debug("end to cascadeSetVideoSelection");
        }
    }