opencv将视频按比例缩放到设定的分辨率上，多余部分黑色补齐

原版视频是1280*720的，如下图所示。

想将视频按比例缩放到设定的分辨率上，原版视频放在中央，上下左右多余部分黑色补齐。例如我设定分辨率是1280*384的，效果如下：

通过opencv的python版代码如下(图片同理)：

import cv2
 
# 输入输出视频路径
input_video_path = 'crossroad.mp4'
output_video_path = 'crossroad_resize.mp4'
 
# 设置新的分辨率大小
target_width = 1280
target_height = 384
 
# 创建VideoCapture对象
cap = cv2.VideoCapture(input_video_path)
# 获取原始视频帧的大小
origin_width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
origin_height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

# 计算缩放比例
ratio_w = target_width / origin_width
ratio_h = target_height / origin_height
scale = min(ratio_w, ratio_h)
# 计算新尺寸
resized_width = int(origin_width * scale)
resized_height = int(origin_height * scale)

# 获取视频的编码格式和帧率
fourcc = cv2.VideoWriter_fourcc(*'mp4v')
fps = cap.get(cv2.CAP_PROP_FPS)
 
# 构造补齐值
pad_value = (0,0,0)
# 构造补齐后图片的位置
pad_h = max(target_height - resized_height, 0)
pad_w = max(target_width - resized_width, 0)
pad_top = pad_h // 2
pad_bottom = pad_h - pad_top
pad_left = pad_w // 2
pad_right = pad_w - pad_left

# 创建VideoWriter对象
out = cv2.VideoWriter(output_video_path, fourcc, fps, (target_width, target_height))

# 读取视频帧并调整大小
while cap.isOpened():
    ret, frame = cap.read()
    if ret:
        # 调整帧大小
        resized_frame = cv2.resize(frame, (resized_width, resized_height), interpolation=cv2.INTER_AREA)

        padded_frame = cv2.copyMakeBorder(resized_frame, pad_top, pad_bottom, pad_left, pad_right, cv2.BORDER_CONSTANT, value=pad_value)
        
        # 显示原始帧和调整大小的帧
        cv2.imshow('Resized Frame', padded_frame)

        # 写入调整大小的帧
        out.write(padded_frame)

        # 按'q'退出循环
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    else:
        break
 
# 释放对象
cap.release()
out.release()