The source code is in /opt/nvidia/deepstream/deepstream/sources/apps
DeepStream SDK use nvegltransform and nveglglessink to display the GPU processed data. DeepStream SDK FAQ - Intelligent Video Analytics / DeepStream SDK - NVIDIA Developer Forums
The deepstream-app pipeline for v4l2src has no “videoconvert” for Jetson. Please refer to the source code.
You camera only support 30FPS framerate, why do you set 20FPS in the deepstream-app config file?
You may check whether the following pipeline works or not with the camera.
gst-launch-1.0 v4l2src ! 'video/x-raw, framerate=30/1',width=640,height=480' ! nvvideoconvert ! 'video/x-raw(memory:NVMM),format=NV12' ! nvvideoconvert ! 'video/x-raw(memory:NVMM),format=RGBA' ! nvegltransform ! nveglglessink