外接usb3.0 camera编码延迟较大，2560*1920一帧编码延迟为50ms左右

[fanzh]

1. please refer to this faq How to connect a USB camera in DeepStream . can the v4l2src output video stably?
2. could you share the deepstream-app configuration file?
3. to narrow down this issue, what is the Encode Latency and encoder utilization of this pipeline? you can use “sudo tegrastats” to get encoder utilization.
   gst-launch-1.0 -v videotestsrc ! video/x-raw,format=YUY2,width=2560,height=1920 ! videoconvert ! nvvideoconvert ! nvv4l2h264enc ! fakesink