public boolean nextPacket(){
    	if(_finished == true){
    		return false;
    	}
	    while (true){
	    	int state = container.readNextPacket(packet);
	    	//直到获取视频流中的一段码流
	        if(state < 0){
	        	_finished = true; //视频已经读取完毕
	        	return false;
	        }else{
    	    	if(packet.getStreamIndex() == videoStreamId){
    	    		offsetInPacket = 0;
    	    		return true;  //读取视频码流完毕
    	    	}else{
    	    		continue;  //不是视频流，读取下一个码流packet
    	    	}
	        }	
	    }
    }