Python+OpenCV讀寫視訊的方法詳解

import cv2

video_capture = cv2.VideoCapture(video_path)
while True:
    flag, frame = video_capture.read()
    if not flag:
        break
    # do something with frame
video_capture.release()

import cv2

video_path = r'D:peppaMuddy_Puddles.mp4'
video_capture = cv2.VideoCapture(video_path)

frame_num = video_capture.get(cv2.CAP_PROP_FRAME_COUNT) # ==> 總幀數
fps = video_capture.get(cv2.CAP_PROP_FPS)               # ==> 影格率
width = video_capture.get(cv2.CAP_PROP_FRAME_WIDTH)     # ==> 視訊寬度
height = video_capture.get(cv2.CAP_PROP_FRAME_HEIGHT)   # ==> 視訊高度
pos = video_capture.get(cv2.CAP_PROP_POS_FRAMES)        # ==> 控制程式碼位置

video_capture.set(cv2.CAP_PROP_POS_FRAMES, 1000)        # ==> 設定控制程式碼位置
pos = video_capture.get(cv2.CAP_PROP_POS_FRAMES)        # ==> 此時 pos = 1000.0

video_capture.release()

import cv2
import numpy as np

video_path = r'D:peppaMuddy_Puddles.mp4'
video_capture = cv2.VideoCapture(video_path)
cnt = -1
frames1 = []
while True:
    cnt += 1
    flag, frame = video_capture.read()
    assert flag
    if 100 <= cnt < 200:
        frames1.append(frame)
    if cnt >= 200:
        break
video_capture.release()

video_capture = cv2.VideoCapture(video_path)
frames2 = []
for i in range(100, 200):
    video_capture.set(cv2.CAP_PROP_POS_FRAMES, i)
    flag, frame = video_capture.read()
    assert flag
    frames2.append(frame)
video_capture.release()

frames1 = np.array(frames1)
frames2 = np.array(frames2)
print(np.all(frames1 == frames2))  # ==> check whether frames1 is same as frames2, result is True

import cv2
import numpy as np
import time

video_path = r'D:peppaMuddy_Puddles.mp4'
video_capture = cv2.VideoCapture(video_path)
t0 = time.time()
while True:
    flag, frame = video_capture.read()
    if not flag:
        break
t1 = time.time()
video_capture.release()

video_capture = cv2.VideoCapture(video_path)
t2 = time.time()
frame_num = int(video_capture.get(cv2.CAP_PROP_FRAME_COUNT))
for i in range(frame_num):
    video_capture.set(cv2.CAP_PROP_POS_FRAMES, i)
    flag, frame = video_capture.read()
    assert flag
t3 = time.time()
video_capture.release()

print(t1 - t0)  # ==> 76.3 s
print(t3 - t2)  # ==> 345.1 s

# -*- coding: utf-8 -*-
import os
import cv2


def _extract_frame_mode_1(video_capture, frame_list, root_folder, ext='png'):
    """
    extract video frames and save them to disk. this method will go through all
    the frames using video_capture.read()

    Parameters:
    -----------
    video_capture: obtained by cv2.VideoCapture()
    frame_list: list
        list of frame numbers
    root_folder: str
        root folder to save frames
    ext: str
        extension of filename
    """
    frame_list = sorted(frame_list)
    video_capture.set(cv2.CAP_PROP_POS_FRAMES, 0)
    cnt = -1
    index = 0
    while True:
        cnt += 1
        flag, frame = video_capture.read()
        if not flag:
            break
        if cnt == frame_list[index]:
            filename = os.path.join(root_folder, str(cnt) + '.' + ext)
            cv2.imwrite(filename, frame)
            index += 1


def _extract_frame_mode_2(video_capture, frame_list, root_folder, ext='png'):
    """
        extract video frames and save them to disk. this method will use
        video_capture.set() to locate the frame position and then use
        video_capture.read() to read

        Parameters:
        -----------
        video_capture: obtained by cv2.VideoCapture()
        frame_list: list
            list of frame numbers
        root_folder: str
            root folder to save frames
        ext: str
            extension of image filename
        """
    for i in frame_list:
        video_capture.set(cv2.CAP_PROP_POS_FRAMES, i)
        flag, frame = video_capture.read()
        assert flag
        filename = os.path.join(root_folder, str(i) + '.' + ext)
        cv2.imwrite(filename, frame)


def extract_frame(video_path, increment=None, frame_list=None,
                  mode=1, ext='png'):
    """
    extract video frames and save them to disk. the root folder to save frames
    is same as video_path (without extension)
    
    Parameters:
    -----------
    video_path: str
        video path
    increment: int of 'fps'
        increment of frame indexes
    frame_list: list
        list of frame numbers
    mode: int, 1 or 2
        1: go through all the frames using video_capture.read()
        2: use video_capture.set() to locate the frame position and then use
        video_capture.read() to read
    ext: str
        extension of image filename
    """
    video_capture = cv2.VideoCapture(video_path)
    frame_num = int(video_capture.get(cv2.CAP_PROP_FRAME_COUNT))

    if increment is None:
        increment = 1
    elif increment == 'fps':
        fps = video_capture.get(cv2.CAP_PROP_FPS)
        increment = round(fps)

    if frame_list is None:
        frame_list = [i for i in range(0, frame_num, increment)]

    if frame_num // len(frame_list) > 5 and mode == 1:
        print("the frames to be extracted is too sparse, "
              "please consider setting mode = 2 to accelerate")

    root_folder = os.path.splitext(video_path)[0]
    os.makedirs(root_folder, exist_ok=True)
    if mode == 1:
        _extract_frame_mode_1(video_capture, frame_list, root_folder, ext)
    elif mode == 2:
        _extract_frame_mode_2(video_capture, frame_list, root_folder, ext)
    video_capture.release()


if __name__ == '__main__':
    video_path = r'D:peppaMuddy_Puddles.mp4'
    extract_frame(video_path, increment=30, mode=2)

video_path = r'D:peppaMuddy_Puddles.avi'
root_folder = r'D:peppaMuddy_Puddles'

fourcc = cv2.VideoWriter_fourcc('X', 'V', 'I', 'D')
fps = 25
size = (1920, 1080)

video_writer = cv2.VideoWriter(video_path, fourcc, fps, size)
for i in range(0, 7788, 30):
    filename = os.path.join(root_folder, str(i) + '.png')
    image = cv2.imread(filename)
    video_writer.write(image)
video_writer.release()