Hi,
Encoder does not support RGBA. Please try to link to one more nvvidconv to conver to NV12 like:
... ! nvvidconv name=myconv ! video/x-raw(memory:NVMM),format=RGBA ! nvvidconv ! video/x-raw(memory:NVMM),format=NV12 ! nvv4l2h264enc bitrate=8000000 ! ...
You may also try the reference sample:
Nano not using GPU with gstreamer/python. Slow FPS, dropped frames - #8 by DaneLLL