How to encode a HEVC video from YUV420 Mat data (from a hardware triggered camera) via FFmpeg in Python

Question

I am having problems encoding a HEVC video from a series of YUV420 Mat data via FFmpeg.

1. I am using python in Ubuntu-20.04;
2. I am retrieving frame data from a hardware triggered camera (BASLER), using pypylon;
3. I want to write a video from that camera in HEVC codec, using my GPU-NVENC;
4. I guess I have to use FFmpeg to achieve these;

What I have tried:

1. I find that FFmpeg supports encoding from a camera, but it seems to only support webcams, not the camera I use (hardware triggered BASLER cameras with pypylon APIs);
2. I find that FFmpeg supports transfering a video from one codec to another, which is not my case;
3. I find that FFmpeg supports encoding a video from a series of jpeg images. But in my case, it will be inefficient if I first save each frame into a picture and then encode them into a video;
4. The frame data retrieved from camera can be converted to YUV420 (directly from pypylon), which is suitable for HEVC encoding;
5. I learnt that the basic unit in FFmpeg to encode a video is AVFrame. I guess I have to first turn my YUV420 data into AVFrame, then encode AVFrames into HEVC;
6. But I do not know how to achieve that in python.

My simplified and expected codes:

camera = pylon.InstantCamera(tlf.CreateFirstDevice())
converter = pylon.ImageFormatConverter()
converter.OutputPixelFormat = pylon.PixelType_YUV420
video_handle = xxxxxx  # HEVC
while True:
    grabResult = camera.RetrieveResult(timeout, pylon.TimeoutHandling_ThrowException)
    image = converter.Convert(grabResult).GetArray()
    video_handle.write(frame)  # encode into a hevc video via ffmpeg in NVENC