gstCamera::Capture() -- an error occurred retrieving the next image buffer

[gualua]

first question

Excuse me, I can't get img when i launch commands as follow:
import jetson.utils
import jetson.inference
input = jetson.utils.videoSource("/dev/video0") # USB摄像头
output = jetson.utils.videoOutput("display://0") # 显示输出窗口
net = jetson.inference.detectNet("ssd-mobilenet-v2", threshold=0.5)
while output.IsStreaming():
img = input.Capture()
if img is None:
print("Failed to capture image") # 调试信息
continue # 如果捕获失败，跳过这次循环
detections = net.Detect(img)
output.Render(img)
output.SetStatus("Performance {:.0f} FPS".format(net.GetNetworkFPS()))

I will get errors as below:
File "/home/gdcx/jetson-inference/obdetection1.py", line 13, in
img = input.Capture()
Exception: jetson.utils -- videoSource failed to capture image

second question

when I launch this command: &detectnet /dev/video0
i will get this problem as follow:
[TRT] note -- when processing a single image, run 'sudo jetson_clocks' before
to disable DVFS for more accurate profiling/timing measurements

[cuda] cudaGetLastError()
[cuda] unknown error (error 999) (hex 0x3E7)
[cuda] /home/gdcx/jetson-inference/utils/cuda/cudaYUV-YV12.cu:119
[cuda] cudaI420ToRGB(input, (uchar3*)output, width, height, stream)
[cuda] unknown error (error 999) (hex 0x3E7)
[cuda] /home/gdcx/jetson-inference/utils/cuda/cudaColorspace.cpp:54
[cuda] cudaConvertColor(latestYUV, mFormatYUV, nextRGB, format, mOptions->width, mOptions->height, stream)
[cuda] unknown error (error 999) (hex 0x3E7)
[cuda] /home/gdcx/jetson-inference/utils/codec/gstBufferManager.cpp:445
[gstreamer] gstBufferManager -- unsupported image format (rgb8)
[gstreamer] supported formats are:
[gstreamer] * rgb8
[gstreamer] * rgba8
[gstreamer] * rgb32f
[gstreamer] * rgba32f
[gstreamer] gstCamera::Capture() -- an error occurred retrieving the next image buffer

End

**:How can i solve this problem ? Why can't i get img with USB camera?