Opencv载取任意长度视频

使用Opencv截取仍意长度视频。

import cv2
import sys

def select_video(input_path,output_path,start=1,end=-1):
    """
    input_path表示原视频路径
    output_path表示要保存路径
    start表示起始的帧,默认从头开始
    end表示终止帧，默认到结尾
    """
    assert start<end,"起始帧位置要小于终止帧位置"
    cap = cv2.VideoCapture(input_path)
    if not cap.isOpened():
        print("Cannot open camera")
        exit()
    # print()
#     fps = int(cap.get(cv2.CAP_PROP_FPS)) #有些文件该值无法获取
    fps = 25
    width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
    height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
    size =(width,height)
    print('fps',fps)
    print('size',size)

    num_frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))# 该值有时也读不出来要注意
    if num_frames<0:
        num_frames=end
 
    fourcc = cv2.VideoWriter_fourcc(*'mp4v') # *'XVID' 保存AVI视频
    out = cv2.VideoWriter(output_path, fourcc, fps,(width, height), True)
    i =  1 
    j =  0 
    end = min(end,num_frames)
    while True:
        ret, frame = cap.read()
        if not ret:
            print("Can't receive frame (stream end?). Exiting...")
            break   
        if i>=start and i <=end:
            out.write(frame)
            j  = j+1
        i = i+1
        if i>end:
            print("\nfinished all ")
            break
        sys.stdout.write('\r%d/%d finished!' %(j,end-start+1))
        sys.stdout.flush() 

    cap.release()
    out.release()