Process Video and Camera

Process Video and Camera

1. cv.2VideoCapture Class

• cv.VideoCapture class could do the task that recieves the frame from cammer or video in OpenCV.

2. Open Cammera

cv2.VideoCapture(index,apiPreference=None) -> retval

• index : camera_id + domain_offset_id (If you open the system basic cammer using the basic method,pass “0” to index. )
• apiPrefence : Specified as prefered cammera processing method.
• retval : cv2.VideoCapture object

cv2.VideoCapture.open(index,apiPreference=None) -> retval

• retval : To success is True, To fail is False

3. open Video, Stop video sequence, Video stream

cv2.VideoCapture(filename, apiPreference = None) -> retval

• filename : Video file name, stop video sequence , video stream URL etc. ex) ‘video.avi’, ‘img_%02d.jpg’,’protocol://host:prot/scrpt?params

  auth’

• apiPreference : Specify as prefered cammera processing method
• retval : cv2.VideoCapture object

cv2.VideoCapture.open(filename,apiPreference=None) -> retval

• retval : To success is True, To fail is False

4. Check the Video capture

cv2.VideoCaptrue.isOpened() ->> retval

• retval : To success is True, To fail is False

5. Recieve the frame

cv2.VideoCapture.read(image=None) -> retval, image

• retval : To success is True, To fail is False
• image : Current frame ( numpy.ndarray)

6. To refer Cammera, Video device property value

cv2.VideoCapture.get(propID) -> retval

• propID : property constant

|—|—| |CAP_PROP_FRAME_WIDTH|frame horizontal size| |CAP_PROP_FRAME_HEIGHT|frame vertical size| |CAP_PROP_FPS|the number of frames per second| |—|—|

7. cv2.VideoWriter class

• The frames are could saved as video file using cv.VideoWriter class in OpenCV.

• Fourcc(four chracter code) : integer value defining codec of video file, method of compress, color, pixel

|—|—| |cv2.VideoWriter_fourcc(‘DIVX’)|DIVC MPEG-4 codec| |cv2.VideoWriter_fourcc(‘XIVD’)|XCID MPEG-4 codec| |cv2.VideoWriter_fourcc(‘FMP$’)|DDMPEG MPEG-4 codec| |cv2.VideoWriter_fourcc(‘X264’)|G.264/AVC codec| |cv2.VideoWriter_fourcc(*‘MJPG’)|Motion-JPEG codec| |—|—|

8. open the video file for storage

cv2.VideoWriter(filename, fourcc, fps, frameSize, isColor=None) -> retval

• filename : video file name
• fourcc : fourcc ex) cv2.VideoWriter_fourcc(*‘DIVX’))
• fps : the number of frame per second ex) 30
• frame size : (width,height)
• isColor : Color video is True

cv2.VideoWriter.open(filename, fourcc, fps, frameSie, isColor=None) -> retval

9. Check the video file

cv2.VideoWriter.isOpend() -> retval

• save the frame

  cv2.VideoWriter.write(image) -> None
  

• image : To save frame (numpy.ndarray)

10. save the video for WebCam input

 
cap = cv2.VideoCapture(0)
w = round(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
h = round(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

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

out = cv2.VideoWriter('output.avi', fourcc, 30, (w, h))

while True:
    ret, frame = cap.read()
    
    inversed = ~frame 
    out.write(inversed)
    
    cv2.imshow('frame', frame) 
    cv2.imshow('inversed', inversed) 
    
    if cv2.waitKey(10) == 27:
        break