numpy类型转ExternalVideoFrame类型

```python
i420_array = cv2.cvtColor(bgr_array, cv2.COLOR_BGR2YUV_I420)

external_video_frame = ExternalVideoFrame()
external_video_frame.type = 1
external_video_frame.format = 1 # 设置为I420格式，对应的值为1
external_video_frame.buffer = bytearray(i420_array.tobytes())
external_video_frame.stride = i420_array.shape[1]
external_video_frame.height = i420_array.shape[0]
sender.send_video_frame(external_frame) # sender为VideoFrameSender类型
```

运行发送代码，程序直接奔溃
```
Segmentation fault (core dumped)
```

由numpy类型的BGR数组到type值分别为0、1、4的ExternalVideoFrame对象的正确转换方式应该是怎样的？