python利用opencv儲存、播放視訊
阿新 • • 發佈:2020-11-04
程式碼已上傳至:https://gitee.com/tqbx/python-opencv/tree/master/Getting_started_videos
目標
學習讀取視訊,播放視訊,儲存視訊。
學習從相機中捕捉幀並展示。
學習cv2.VideoCapture(),cv2.VideoWriter()的使用
從相機中捕捉視訊
通過自帶攝像頭捕捉視訊,並將其轉化為灰度視訊顯示出來。
基本步驟如下:
1.首先建立一個VideoCapture物件,它的引數包含兩種:
- 裝置索引,指定攝像機的編號。
- 視訊檔案的名稱。
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()
返回布林值,如果frame讀取正確,為True,可以通過這個值判斷視訊是否已經結束。- 有時,cap可能會初始化捕獲失敗,可以通過
cap.isOpened()
來檢查其是否被初始化,如果為True那是最好,如果不是,可以使用cap.open()
來嘗試開啟它。 - 當然,你可以使用
cap.get(propId)
的方式獲取視訊的一些屬性,如幀的寬度,幀的高度,幀速等。propId是0-18的數字,每個數字代表一個屬性,對應關係見底部附錄。 - 既然可以獲取,當然也可以嘗試設定,假設想要設定幀的寬度和高度為320和240:
cap.set(3,320),cap.set(4,240)
從檔案中播放視訊
程式碼和從相機中捕獲視訊基本相同,不同之處在於傳入VideoCapture的引數,此時傳入視訊檔案的名稱。
在顯示每一幀的時候,可以使用cv2.waitKey()
設定適當的時間,如果值很小,視訊將會很快。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()
儲存視訊
1.建立一個VideoWriter 物件,指定如下引數:
- 輸出的檔名,如output.avi。
- FourCC code。
- 每秒的幀數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是一個用於指定視訊編解碼器的4位元組程式碼。
- 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)
參考閱讀
Getting Started with Videos
作者:天喬巴夏丶
出處:https://www.cnblogs.com/summerday152/
本文已收錄至Gitee:https://gitee.com/tqbx/JavaBlog
若有興趣,可以來參觀本人的個人小站:https://www.hyhwky.com
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