Capture and Save IP Camera in Python OpenCV

- by mahmood 
import cv2

#print("Before URL")
cap = cv2.VideoCapture('rtsp://admin@192.168.10.29:554/cam/realmonitor?channel=1&subtype=1')
#print("After URL")

(grabbed, frame) = cap.read()
fshape = frame.shape
fheight = fshape[0]
fwidth = fshape[1]
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (fwidth,fheight))

while True:

    #print('About to start the Read command')
    ret, frame = cap.read()
    #print('About to show frame of Video.')
    cv2.imshow("Capturing",frame)
    #print('Running..')

    out.write(frame)

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

cap.release()
cv2.destroyAllWindows()

References
https://pupli.net/2021/01/access-ip-camera-in-python-opencv/
https://stackoverflow.com/questions/29317262/opencv-video-saving-in-python

Access IP Camera in Python OpenCV

- by mahmood 
import cv2

#print("Before URL")
cap = cv2.VideoCapture('rtsp://admin:123456@192.168.1.216/H264?ch=1&subtype=0')
#print("After URL")

while True:

    #print('About to start the Read command')
    ret, frame = cap.read()
    #print('About to show frame of Video.')
    cv2.imshow("Capturing",frame)
    #print('Running..')

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

cap.release()
cv2.destroyAllWindows()

References
https://stackoverflow.com/questions/49978705/access-ip-camera-in-python-opencv
https://dahuawiki.com/Remote_Access/RTSP_via_VLC

Disable swap on Ubuntu

- by mahmood

disable swap only for a current session

sudo swapoff -a

Or 

sudo -s
crontab -e

And add

@reboot sudo swapoff -a

Or ( best solution )

Open fstab file, type sudo nano /etc/fstab in terminal.

File’s contents would look like this:

proc            /proc           proc    nodev,noexec,nosuid 0       0
/host/ubuntu/disks/root.disk /               ext4    loop,errors=remount-ro 0       1
/host/ubuntu/disks/swap.disk none            swap    loop,sw         0       0
#/dev/sda10 /media/ASD  vfat    defaults    0   0
#/dev/sda1  /media/98   vfat    defaults    0   0

Just add hash (#) to the beginning of the swap partition line, so the line looks as:

#/host/ubuntu/disks/swap.disk none            swap    loop,sw         0       0

Reboot your PC

References
https://askubuntu.com/questions/214805/how-do-i-disable-swap

SQLite3 and multiple processes

- by mahmood

First, avoid concurrent access to sqlite database files. Concurrency is one of sqlite’s weak points and if you have a highly concurrent application, consider using another database engine.

If you cannot avoid concurrency or drop sqlite, wrap your write transactions in BEGIN IMMEDIATE; … END;. The default transaction mode in sqlite is DEFERRED which means that a lock is acquired only on first actual write attempt. With IMMEDIATE transactions, the lock is acquired immediately, or you get SQLITE_BUSY immediately. When someone holds a lock to the database, other locking attempts will result in SQLITE_BUSY.

Dealing with SQLITE_BUSY is something you have to decide for yourself. For many applications, waiting for a second or two and then retrying works quite all right, giving up after n failed attempts. There are sqlite3 API helpers that make this easy, e.g. sqlite3_busy_handler() and sqlite3_busy_timeout() but it can be done manually as well.

You could also use OS level synchronization to acquire a mutex lock to the database, or use OS level inter-thread/inter-process messaging to signal when one thread is done accessing the database.

If you want to use Python’s automatic transaction handling, leave isolation_level at its default value, or set it to one of the three levels.

If you want to do your own transaction handling, you have to prevent Python from doing its own by setting isolation_level to None.

References
https://stackoverflow.com/questions/1063438/sqlite3-and-multiple-processes
https://stackoverflow.com/questions/41915603/python3-sqlite3-begin-immediate-error