python利用opencv保存、播放視頻

更新時(shí)間：2020年11月02日 09:52:55 作者：天喬巴夏丶

這篇文章主要介紹了python利用opencv保存、播放視頻，幫助大家更好的利用python處理視頻，感興趣的朋友可以了解下

代碼已上傳至：https://gitee.com/tqbx/python-opencv/tree/master/Getting_started_videos

目標(biāo)

學(xué)習(xí)讀取視頻，播放視頻，保存視頻。
學(xué)習(xí)從相機(jī)中捕捉幀并展示。
學(xué)習(xí)cv2.VideoCapture()，cv2.VideoWriter()的使用

從相機(jī)中捕捉視頻

通過(guò)自帶攝像頭捕捉視頻，并將其轉(zhuǎn)化為灰度視頻顯示出來(lái)。

基本步驟如下：

1.首先創(chuàng)建一個(gè)VideoCapture對(duì)象，它的參數(shù)包含兩種：

設(shè)備索引，指定攝像機(jī)的編號(hào)。
視頻文件的名稱。

2.逐幀捕捉。

3.釋放捕捉物。

import numpy as np
import cv2 as cv
cap = cv.VideoCapture(0)
if not cap.isOpened():
  print("Cannot open camera")
  exit()
while True:
  # Capture frame-by-frame
  ret, frame = cap.read()
  # if frame is read correctly ret is True
  if not ret:
    print("Can't receive frame (stream end?). Exiting ...")
    break
  # Our operations on the frame come here
  gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
  # Display the resulting frame
  cv.imshow('frame', gray)
  if cv.waitKey(1) == ord('q'):
    break
# When everything done, release the capture
cap.release()
cv.destroyAllWindows()

其他：

cap.read()返回布爾值，如果frame讀取正確，為T(mén)rue，可以通過(guò)這個(gè)值判斷視頻是否已經(jīng)結(jié)束。
有時(shí)，cap可能會(huì)初始化捕獲失敗，可以通過(guò)cap.isOpened()來(lái)檢查其是否被初始化，如果為T(mén)rue那是最好，如果不是，可以使用cap.open()來(lái)嘗試打開(kāi)它。
當(dāng)然，你可以使用cap.get(propId)的方式獲取視頻的一些屬性，如幀的寬度，幀的高度，幀速等。propId是0-18的數(shù)字，每個(gè)數(shù)字代表一個(gè)屬性，對(duì)應(yīng)關(guān)系見(jiàn)底部附錄。
既然可以獲取，當(dāng)然也可以嘗試設(shè)置，假設(shè)想要設(shè)置幀的寬度和高度為320和240：cap.set(3,320), cap.set(4,240)。

從文件中播放視頻

代碼和從相機(jī)中捕獲視頻基本相同，不同之處在于傳入VideoCapture的參數(shù)，此時(shí)傳入視頻文件的名稱。

在顯示每一幀的時(shí)候，可以使用cv2.waitKey()設(shè)置適當(dāng)?shù)臅r(shí)間，如果值很小，視頻將會(huì)很快。正常情況下，25ms就ok。

import numpy as np
import cv2

cap = cv2.VideoCapture('vtest.avi')

while(cap.isOpened()):
  ret, frame = cap.read()

  gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

  cv2.imshow('frame',gray)
  if cv2.waitKey(1) & 0xFF == ord('q'):
    break

cap.release()
cv2.destroyAllWindows()

保存視頻

1.創(chuàng)建一個(gè)VideoWriter 對(duì)象，指定如下參數(shù)：

輸出的文件名，如output.avi。
FourCC code。
每秒的幀數(shù)fps。
幀的size。

2.FourCC code傳遞有兩種方式：

fourcc = cv2.VideoWriter_fourcc(*'XVID')
fourcc = cv2.VideoWriter_fourcc('X','V','I','D')

3.FourCC是一個(gè)用于指定視頻編解碼器的4字節(jié)代碼。

In Fedora: DIVX, XVID, MJPG, X264, WMV1, WMV2. (XVID is more preferable. MJPG results in high size video. X264 gives very small size video)
In Windows: DIVX (More to be tested and added)
In OSX : (I don't have access to OSX. Can some one fill this?)

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

# Define the codec and create VideoWriter object
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))

while(cap.isOpened()):
  ret, frame = cap.read()
  if ret==True:
    frame = cv2.flip(frame,0)

    # write the flipped frame
    out.write(frame)

    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
      break
  else:
    break

# Release everything if job is finished
cap.release()
out.release()
cv2.destroyAllWindows()

附錄

CV_CAP_PROP_POS_MSEC Current position of the video file in milliseconds or video capture timestamp.
CV_CAP_PROP_POS_FRAMES 0-based index of the frame to be decoded/captured next.
CV_CAP_PROP_POS_AVI_RATIO Relative position of the video file: 0 - start of the film, 1 - end of the film.
CV_CAP_PROP_FRAME_WIDTH Width of the frames in the video stream.
CV_CAP_PROP_FRAME_HEIGHT Height of the frames in the video stream.
CV_CAP_PROP_FPS Frame rate.
CV_CAP_PROP_FOURCC 4-character code of codec.
CV_CAP_PROP_FRAME_COUNT Number of frames in the video file.
CV_CAP_PROP_FORMAT Format of the Mat objects returned by retrieve() .
CV_CAP_PROP_MODE Backend-specific value indicating the current capture mode.
CV_CAP_PROP_BRIGHTNESS Brightness of the image (only for cameras).
CV_CAP_PROP_CONTRAST Contrast of the image (only for cameras).
CV_CAP_PROP_SATURATION Saturation of the image (only for cameras).
CV_CAP_PROP_HUE Hue of the image (only for cameras).
CV_CAP_PROP_GAIN Gain of the image (only for cameras).
CV_CAP_PROP_EXPOSURE Exposure (only for cameras).
CV_CAP_PROP_CONVERT_RGB Boolean flags indicating whether images should be converted to RGB.
CV_CAP_PROP_WHITE_BALANCE_U The U value of the whitebalance setting (note: only supported by DC1394 v 2.x backend currently)
CV_CAP_PROP_WHITE_BALANCE_V The V value of the whitebalance setting (note: only supported by DC1394 v 2.x backend currently)
CV_CAP_PROP_RECTIFICATION Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently)
CV_CAP_PROP_ISO_SPEED The ISO speed of the camera (note: only supported by DC1394 v 2.x backend currently)
CV_CAP_PROP_BUFFERSIZE Amount of frames stored in internal buffer memory (note: only supported by DC1394 v 2.x backend currently)