rk3399pro使用opencv调用gstreamer出错

首先我按步骤编译安装了Mpp和gstreamer-rockchip，然后用以下shell命令成功硬解视频

1. gst-launch-1.0 filesrc location=/home/toybrick/yolov5/test_data/20210728105542_1km.mp4 ! decodebin ! rkximagesink

复制代码但是我使用opencv调用gstreamer时

1. gst='filesrc location=/home/toybrick/yolov5/test_data/20210728105542_1km.mp4 ! decodebin ! rkximagesink'
   
2. cap = cv.VideoCapture(gst,cv.CAP_GSTREAMER)
   
3. 
   
4. if not cap.isOpened():
   
5.     print("Cannot capture from camera. Exiting.")
   
6.     #os._exit()
   
7. 
   
8. while(True):
   
9. 
   
10.     ret, frame = cap.read()
    
11.     if ret:
    
12.         cv.imshow('frame', frame)
    
13. 
    
14.     if cv.waitKey(1) & 0xFF == ord('q'):
    
15.         break
    
16. 
    
17. cap.release()
    
18. cv.destroyAllWindows()

复制代码出现了以下错误：

1. root@debian10:/home/toybrick/yolov5# python gstreamer.py
   
2. [ WARN:0] OpenCV | GStreamer warning: cannot find appsink in manual pipeline
   
3. [ WARN:0] OpenCV | GStreamer warning: GStreamer: pipeline have not been created
   
4. Cannot capture from camera. Exiting.

复制代码按理说opencv调用gstreamer的方法和直接在shell中调用的方法应该是差不多的，为啥会出现这种错误