Capturing video from two cameras in OpenCV at once

I have use “imutils” and read webcam show on the image.

import imutils

capture vedio frames

#--- WebCam1
cap = cv2.VideoCapture(0)
cap.set(cv2.CAP_PROP_FRAME_WIDTH,300)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT,300)
#--- WebCam2
cap1 = cv2.VideoCapture(1)
cap1.set(cv2.CAP_PROP_FRAME_WIDTH,300)
cap1.set(cv2.CAP_PROP_FRAME_HEIGHT,300)
#--- WebCam3
cap2 = cv2.VideoCapture(2)
cap2.set(cv2.CAP_PROP_FRAME_WIDTH,300)
cap2.set(cv2.CAP_PROP_FRAME_HEIGHT,300)
#--- WebCame4
cap3 = cv2.VideoCapture(3)
cap3.set(cv2.CAP_PROP_FRAME_WIDTH,300)
cap3.set(cv2.CAP_PROP_FRAME_HEIGHT,300)

i create function read_frame send parameter about Image.fromarray and display

def read_frame():
    webCameShow(cap.read(),display1)
    webCameShow(cap1.read(),display2)
    webCameShow(cap2.read(),display6)
    webCameShow(cap3.read(),display7)   
    window.after(10, read_frame)

and final function show video on the “imageFrame”

def webCameShow(N,Display): 
    _, frameXX = N
    cv2imageXX = cv2.cvtColor(frameXX, cv2.COLOR_BGR2RGBA)
    imgXX = Image.fromarray(cv2imageXX)
    #imgtkXX = ImageTk.PhotoImage(image=imgXX)
    Display.imgtk = imgtkXX 
    Display.configure(image=imgtkXX)

example.
4-webcam

Youtube:
Youtube

Using OPENCV and two standard USB cameras, I was able to do this using multithreading. Essentially, define one function which opens an opencv window and VideoCapture element. Then, create two threads with the camera ID and window name as inputs.

import cv2
import threading

class camThread(threading.Thread):
    def __init__(self, previewName, camID):
        threading.Thread.__init__(self)
        self.previewName = previewName
        self.camID = camID
    def run(self):
        print "Starting " + self.previewName
        camPreview(self.previewName, self.camID)

def camPreview(previewName, camID):
    cv2.namedWindow(previewName)
    cam = cv2.VideoCapture(camID)
    if cam.isOpened():  # try to get the first frame
        rval, frame = cam.read()
    else:
        rval = False

    while rval:
        cv2.imshow(previewName, frame)
        rval, frame = cam.read()
        key = cv2.waitKey(20)
        if key == 27:  # exit on ESC
            break
    cv2.destroyWindow(previewName)

# Create two threads as follows
thread1 = camThread("Camera 1", 1)
thread2 = camThread("Camera 2", 2)
thread1.start()
thread2.start()

Great resource for learning how to thread in python: https://www.tutorialspoint.com/python/python_multithreading.htm

This has been a pain for me for a long time, so I made a library on top of OpenCV to handle multiple cameras and viewports. I ran into a bunch of problems like videos not compressing by default, or windows only displaying in the main thread. I’m able to display two 720p webcams in real time on Windows so far.

Try:

pip install CVPubSubs

Then, in python:

import cvpubsubs.webcam_pub as w
from cvpubsubs.window_sub import SubscriberWindows

t1 = w.VideoHandlerThread(0)
t2 = w.VideoHandlerThread(1)

t1.start()
t2.start()

SubscriberWindows(window_names=['cammy', 'cammy2'],
              video_sources=[0,1]
              ).loop()

t1.join()
t1.join()

It’s relatively new though, so tell me about any bugs or unoptimized code.

try to use this code…
it worked as expected…
this is for two cams,if you want more cams, just create the “VideoCapture()” objects…for example 3rd cam will have : cv2.VideoCapture(3) and corresponding code in the while loop

import cv2

frame0 = cv2.VideoCapture(1)
frame1 = cv2.VideoCapture(2)
while 1:

   ret0, img0 = frame0.read()
   ret1, img00 = frame1.read()
   img1 = cv2.resize(img0,(360,240))
   img2 = cv2.resize(img00,(360,240))
   if (frame0):
       cv2.imshow('img1',img1)
   if (frame1):
       cv2.imshow('img2',img2)

   k = cv2.waitKey(30) & 0xff
   if k == 27:
      break

frame0.release()
frame1.release()
cv2.destroyAllWindows()

ALL THE BEST !

frame0 = cv2.VideoCapture(1)
frame1 = cv2.VideoCapture(2)

must be:

frame0 = cv2.VideoCapture(0)  # index 0
frame1 = cv2.VideoCapture(1)  # index 1

So it runs

Adding a little to what @TheoreticallyNick posted earlier:

import cv2
import threading

class camThread(threading.Thread):
    def __init__(self, previewName, camID):
        threading.Thread.__init__(self)
        self.previewName = previewName
        self.camID = camID
    def run(self):
        print("Starting " + self.previewName)
        camPreview(self.previewName, self.camID)

def camPreview(previewName, camID):
    cv2.namedWindow(previewName)
    cam = cv2.VideoCapture(camID)
    if cam.isOpened():
        rval, frame = cam.read()
    else:
        rval = False

    while rval:
        cv2.imshow(previewName, frame)
        rval, frame = cam.read()
        key = cv2.waitKey(20)
        if key == 27:  # exit on ESC
            break
    cv2.destroyWindow(previewName)

# Create threads as follows
thread1 = camThread("Camera 1", 0)
thread2 = camThread("Camera 2", 1)
thread3 = camThread("Camera 3", 2)

thread1.start()
thread2.start()
thread3.start()
print()
print("Active threads", threading.activeCount())

This will open up a new thread for each webcam you have. In my case, I wanted to open up three different feeds. Tested on Python 3.6. Let me know if you have any issues, also thanks to TheoreticallyNick for the readable/functioning code!

A bit late, but you can use my VideGear library’s CamGear API that inheritably provide multi-threading and you can write same code in way fewer lines. Also on plus side, all camera streams will be exactly synchronized.

Here’s the example code for two Camera streams:

# import required libraries
from vidgear.gears import VideoGear
import cv2
import time

# define and start the stream on first source ( For e.g #0 index device)
stream1 = VideoGear(source=0, logging=True).start() 

# define and start the stream on second source ( For e.g #1 index device)
stream2 = VideoGear(source=1, logging=True).start() 

# infinite loop
while True:
    
    frameA = stream1.read()
    # read frames from stream1

    frameB = stream2.read()
    # read frames from stream2

    # check if any of two frame is None
    if frameA is None or frameB is None:
        #if True break the infinite loop
        break
    
    # do something with both frameA and frameB here
    cv2.imshow("Output Frame1", frameA)
    cv2.imshow("Output Frame2", frameB)
    # Show output window of stream1 and stream 2 seperately

    key = cv2.waitKey(1) & 0xFF
    # check for 'q' key-press
    if key == ord("q"):
        #if 'q' key-pressed break out
        break

    if key == ord("w"):
        #if 'w' key-pressed save both frameA and frameB at same time
        cv2.imwrite("Image-1.jpg", frameA)
        cv2.imwrite("Image-2.jpg", frameB)
        #break   #uncomment this line to break out after taking images

cv2.destroyAllWindows()
# close output window

# safely close both video streams
stream1.stop()
stream2.stop()

More usage examples can be found here

• Vidgear docs: https://abhitronix.github.io/vidgear
• CamGear docs: https://abhitronix.github.io/vidgear/v0.2.1-stable/gears/camgear/overview/

An option to get around the USB bandwidth limitation is to release the first camera before starting to use the second one, as in

import cv2
cap0 = cv2.VideoCapture(0)
ret0, frame0 = cap0.read()
assert ret0 # succeeds
cap0.release()

cap1 = cv2.VideoCapture(1)
ret1, frame1 = cap1.read()
assert ret1 # succeeds as well

Releasing a camera and opening a new one takes 0.5-1 secs for me, whether this is an acceptable time lag will depend on your use case.

Aside from that and reducing the output resolution of your camera (if the camera allows it…), the only option seems to be to add a PCI USB board for each camera (only really possible on a desktop computer).

Multithreading will not get you around the bandwidth limitation.

This solution might not work for the OP, but this is my experience might help others.

Today I had the same issue on Windows PC. I have 3 webcams from different brands and models. None of the above solutions worked. But I’ve found the issue is that all webcams were connected to the USB2 ports. I connected one of them to a USB3 port and everything worked correctly. At the same time, only one webcam works on USB2 ports. (No difference between front and rear ports in my case) but all webcams work fine if I connect to the rear USB3 ports.