如何在numpy数组中转换视频

import cv2
import numpy as np

video_frames = np.empty((0, height, width, 3), dtype=np.uint8)

cap = cv2.VideoCapture('video.mp4')  # 或者使用摄像头：cap = cv2.VideoCapture(0)

while cap.isOpened():
    ret, frame = cap.read()
    if not ret:
        break
    
    frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)  # 将BGR格式转换为RGB格式
    frame = np.expand_dims(frame, axis=0)  # 添加一个维度，使其成为4维数组
    video_frames = np.concatenate((video_frames, frame), axis=0)

cap.release()

fourcc = cv2.VideoWriter_fourcc(*'mp4v')  # 定义视频编码器
out = cv2.VideoWriter('output.mp4', fourcc, fps, (width, height))

for frame in video_frames:
    frame = cv2.cvtColor(frame, cv2.COLOR_RGB2BGR)  # 将RGB格式转换为BGR格式
    out.write(frame)

out.release()