Saving to file and streaming video and audio on Jetson Nano from a USB 3 webcam

You may try to launch RTSP server through test-launch. Please check
Jetson Nano FAQ
[Q: Is there any example of running RTSP streaming?]

Can try with videotestsrc and audiotestsrc plugins first:
Live streaming cam usb - #4 by DaneLLL
And then apply your audio/video sources.