03_video_cuda_enc sample is not displaying rectangle (multimedia API)

we followed the instructions from https://docs.nvidia.com/jetson/l4t-multimedia/l4t_mm_video_cuda_enc_group.html to build it. but it’s not showing black rectangle on the output encoded video. the black rectangle is supposed to be drawn by GPU, any one faced the same issue? did anyone successfully observe the behavior as explained in the docs. Please helppppppppppp!!!

It may not be obvious in large resolution. Please try 320x240 YUV input. You can generate it by running

$ gst-launch-1.0 videotestsrc num-buffers=300 ! filesink location=a.yuv