The same Vcodec Copy configuration doesn't work on ios 13.5, but it works fine on ios 12.
There is a Hikvision i114 camera, and the following config: 
 "name": "hikcam",
 "manufacturer": "Hikvision",
                    "model": "HiWatch i114",
 "serial number": "192.168.0.15",
                    "firmwareRevision": "1.0",
 "video conference": {
                        "source": "-y-i rtsp://admin:@192.168.0.15:554/unicast",
                        "stillImageSource": "- i rtsp://admin:@192.168.0.15:554/unicast -vframes 1-r 1",
 "vcodec": "copy",
 "package size": 188,
 "audio": true,
 "debug": false
                    } 
On my Iphone x , ios 13.5, the video starts once out of 4-5 attempts. The snapshot is always updated well. And on my son's old iphone 6 on ios12, the video stream always works perfectly! I asked my friends, the same situation!