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How to access camera feed in Jetson Nano

I have tried many attempts to run the cameras connected to my jetson nano. When I run this command:
gst-launch-1.0 -v nvarguscamerasrc ! 'video/x-raw(memory:NVMM),format=NV12,width=1280,height=720,framerate=30/1' ! autovideosink
The camera works but when I try to perform a simple camera read in python with this code
import sys
import cv2
def read_cam():
G_STREAM_TO_SCREEN = "videotestsrc num-buffers=50 ! videoconvert ! appsink"
cap = cv2.VideoCapture(G_STREAM_TO_SCREEN, cv2.CAP_GSTREAMER)
if cap.isOpened():
cv2.namedWindow("demo", cv2.WINDOW_AUTOSIZE)
while True:
ret_val, img = cap.read()
cv2.imshow('demo',img)
cv2.waitKey(1)
else:
print ("Unable to use pipline")
cv2.destroyAllWindows()
if __name__ == '__main__':
read_cam()
the camera does not work in the code above and it returns "Unable to use pipline".
What I am doing wrong and how can I access the camera feed in python?

USB Camera is not detected by OpenCV Python

I am working on a project that has to detect a USB camera (CM3-U3-13S2C-CS a 1.3 Megapixel USB 3.0 camera), opencv failed to detect the id of the camera I have tried the code below to display the IDS of available cameras but all that openCV detects is the ID of the webcam, the camera is working fine on Labview.
I would really appreciate any help !
> import cv2
>
> openCvVidCapIds = []
>
> for i in range(100):
> try:
> cap = cv2.VideoCapture(i)
> if cap is not None and cap.isOpened():
> openCvVidCapIds.append(i)
> # end if
> except:
> pass
> # end try
> # end for
>
> print(str(openCvVidCapIds))

which OS are you running your OpenCV codes? have you checked if your USB camera is shown up in your OS device layers?
for windows, in the Device Manager under the "Imaging devices" tree
for Linux, in /dev like "/dev/video1" and "/dev/video2" and then do
cap =
cv2.VideoCapture("/dev/videox")

How to correctly check if a camera is available?

I am using OpenCV to open and read from several webcams. It all works fine, but I cannot seem to find a way to know if a camera is available.
I tried this code (cam 2 does not exist):
import cv2
try:
c = cv2.VideoCapture(2)
except:
print "Cam 2 is invalid."
But this just prints a lot of errors:
VIDEOIO ERROR: V4L: index 2 is not correct!
failed to open /usr/lib64/dri/hybrid_drv_video.so
Failed to wrapper hybrid_drv_video.so
failed to open /usr/lib64/dri/hybrid_drv_video.so
Failed to wrapper hybrid_drv_video.so
GStreamer Plugin: Embedded video playback halted; module v4l2src0 reported: Internal data stream error.
OpenCV Error: Unspecified error (GStreamer: unable to start pipeline
) in cvCaptureFromCAM_GStreamer, file /builddir/build/BUILD/opencv-3.2.0/modules/videoio/src/cap_gstreamer.cpp, line 832
VIDEOIO(cvCreateCapture_GStreamer(CV_CAP_GSTREAMER_V4L2, reinterpret_cast<char *>(index))): raised OpenCV exception:
/builddir/build/BUILD/opencv-3.2.0/modules/videoio/src/cap_gstreamer.cpp:832: error: (-2) GStreamer: unable to start pipeline
in function cvCaptureFromCAM_GStreamer
OpenCV Error: Unspecified error (unicap: failed to get info for device
) in CvCapture_Unicap::initDevice, file /builddir/build/BUILD/opencv-3.2.0/modules/videoio/src/cap_unicap.cpp, line 139
VIDEOIO(cvCreateCameraCapture_Unicap(index)): raised OpenCV exception:
/builddir/build/BUILD/opencv-3.2.0/modules/videoio/src/cap_unicap.cpp:139: error: (-2) unicap: failed to get info for device
in function CvCapture_Unicap::initDevice
CvCapture_OpenNI::CvCapture_OpenNI : Failed to enumerate production trees: Can't create any node of the requested type!
<VideoCapture 0x7fa5b5de0450>
No exception is thrown. When using c.read() later, I do get False, but I would like to do this in the initialisation phase of my program.
So, how do I find out how many valid cameras I have or check if a certain number 'maps' to a valid one?

Using cv2.VideoCapture( invalid device number ) does not throw exceptions. It constructs a <VideoCapture object> containing an invalid device - if you use it you get exceptions.
Test the constructed object for None and not isOpened() to weed out invalid ones.
For me this works (1 laptop camera device):
import cv2 as cv
def testDevice(source):
cap = cv.VideoCapture(source)
if cap is None or not cap.isOpened():
print('Warning: unable to open video source: ', source)
testDevice(0) # no printout
testDevice(1) # prints message
Output with 1:
Warning: unable to open video source: 1
Example from: https://github.com/opencv/opencv_contrib/blob/master/samples/python2/video.py
lines 159ff
cap = cv.VideoCapture(source)
if 'size' in params:
w, h = map(int, params['size'].split('x'))
cap.set(cv.CAP_PROP_FRAME_WIDTH, w)
cap.set(cv.CAP_PROP_FRAME_HEIGHT, h)
if cap is None or not cap.isOpened():
print 'Warning: unable to open video source: ', source

Another solution, which is available in Linux is to use the /dev/videoX device in the VideoCapture() call. The devices are there when the cam is plugged in. Together with glob(), it is trivial to get all the cameras:
import cv2, glob
for camera in glob.glob("/dev/video?"):
c = cv2.VideoCapture(camera)
Of course a check is needed on c using isOpened(), but you are sure you only scan the available cameras.

Here is a "NOT working" solution to help you prevent tumbling over in this pitfall:
import cv2 as cv
import PySpin
print (cv.__version__)
# provided by Patrick Artner as solution to be working for other cameras than
# those of Point Grey (FLIR).
def testDevice(source):
cap = cv.VideoCapture(source)
if cap is None or not cap.isOpened():
print('Warning: unable to open video source: ', source)
# ... PySpin / Spinnaker (wrapper/SDK libary) ...
system = PySpin.System.GetInstance()
cam_list = system.GetCameras()
cam = ''
cam_num = 0
for ID, cam in enumerate(cam_list):
# Retrieve TL device nodemap
if ID == cam_num:
print ('Got cam')
cam = cam
cam.Init()
# ... CV2 again ...
for i in range(10):
testDevice(i) # no printout

You can try this code:
from __future__ import print_function
import numpy as np
import cv2
# detect all connected webcams
valid_cams = []
for i in range(8):
cap = cv2.VideoCapture(i)
if cap is None or not cap.isOpened():
print('Warning: unable to open video source: ', i)
else:
valid_cams.append(i)
caps = []
for webcam in valid_cams:
caps.append(cv2.VideoCapture(webcam))
while True:
# Capture frame-by-frame
for webcam in valid_cams:
ret, frame = caps[webcam].read()
# Display the resulting frame
cv2.imshow('webcam'+str(webcam), frame)
k = cv2.waitKey(1)
if k == ord('q') or k == 27:
break
# When everything done, release the capture
for cap in caps:
cap.release()
cv2.destroyAllWindows()

How to store webcam video with OpenCV in Python

I've got a script in Python which reads out my webcam and shows it in a window. I now want to store the results, so following this tutorial I wrote the following code:
import cv2
import imutils
camera = cv2.VideoCapture(0)
# Define the codec and create VideoWriter object to save the video
fourcc = cv2.VideoWriter_fourcc(*'XVID')
video_writer = cv2.VideoWriter('output.avi', fourcc, 20.0, (640, 480))
while True:
try:
(grabbed, frame) = camera.read() # grab the current frame
frame = imutils.resize(frame, width=640, height=480)
cv2.imshow("Frame", frame) # show the frame to our screen
key = cv2.waitKey(1) & 0xFF # I don't really have an idea what this does, but it works..
video_writer.write(frame) # Write the video to the file system
except KeyboardInterrupt:
break
# cleanup the camera and close any open windows
camera.release()
video_writer.release()
cv2.destroyAllWindows()
print "\n\nBye bye\n"
This perfectly shows the real time video footage from my webcam in a new window. But writing the video file seems to fail. It does create a file called output.avi, but the file is empty (zero bytes) and on the command line I see the following errors:
OpenCV: Frame size does not match video size.
OpenCV: Frame size does not match video size.
OpenCV: Frame size does not match video size.
etc.
I clearly resize the frame to the size in which I want to save the video (640x480) so I'm not sure why it wouldn't match.
When I run the script again (so in this case the empty output.avi already exists), it shows these errors:
2017-04-17 10:57:14.147 Python[86358:5848730] AVF: AVAssetWriter status: Cannot Save
2017-04-17 10:57:14.332 Python[86358:5848730] mMovieWriter.status: 3. Error: Cannot Save
2017-04-17 10:57:14.366 Python[86358:5848730] mMovieWriter.status: 3. Error: Cannot Save
2017-04-17 10:57:14.394 Python[86358:5848730] mMovieWriter.status: 3. Error: Cannot Save
etc.
In the tutorial it says that the Four digit FourCC code is used to specify the video codec which is platform dependent and that the list of available codes can be found in fourcc.org. I'm on OSX so I tried a bunch of different codec-codes: DIVX, XVID, MJPG, X264, WMV1, WMV2. But unfortunately none of them work for me. They all give the same errors, except for MJPG, which gives me the following error:
OpenCV Error: Assertion failed (img.cols == width && img.rows == height && channels == 3) in write, file /tmp/opencv3-20170216-77040-y1hrk1/opencv-3.2.0/modules/videoio/src/cap_mjpeg_encoder.cpp, line 829
Traceback (most recent call last):
File "store_video.py", line 15, in <module>
video_writer.write(frame) # Write the video to the file system
cv2.error: /tmp/opencv3-20170216-77040-y1hrk1/opencv-3.2.0/modules/videoio/src/cap_mjpeg_encoder.cpp:829: error: (-215) img.cols == width && img.rows == height && channels == 3 in function write
Does anybody know what could be wrong here? All tips are welcome!

It's probably because you built OpenCV with AVFoundation and it doesn't support XVID or other codec. You can try mp4v and m4v extension.
import cv2
camera = cv2.VideoCapture(0)
# Define the codec and create VideoWriter object to save the video
fourcc = cv2.VideoWriter_fourcc('m','p','4','v')
video_writer = cv2.VideoWriter('output.m4v', fourcc, 30.0, (640, 480))
while True:
(grabbed, frame) = camera.read() # grab the current frame
frame = cv2.resize(frame, (640,480))
cv2.imshow("Frame", frame) # show the frame to our screen
key = cv2.waitKey(33) & 0xFF # I don't really have an idea what this does, but it works..
video_writer.write(frame) # Write the video to the file system
if key==27:
break;
# cleanup the camera and close any open windows
camera.release()
video_writer.release()
cv2.destroyAllWindows()
print("\n\nBye bye\n")
On the other note, the error
OpenCV Error: Assertion failed (img.cols == width && img.rows == height && channels == 3) in write, file /tmp/opencv3-20170216-77040-y1hrk1/opencv-3.2.0/modules/videoio/src/cap_mjpeg_encoder.cpp, line 829
means that you messed up the dimension with
frame = imutils.resize(frame, width=640, height=480)
You can try cv2.resize as I used in my code. There's no need to use another library when cv2 can do that already.

Error occuring while connecting USB camera and two arduino with raspberry pi simultaneously

I have the following code for connecting one usb camera and two arduino board with raspberry pi.
import cv2.cv as cv, time
import numpy as np
import serial,time
ser1 = serial.Serial('/dev/ttyUSB0')
ser2 = serial.Serial('/dev/ttyUSB1')
capture = cv.CaptureFromCAM(0)
while True:
try:
for i in range(10):
x = ser1.readline()
with open("test1.txt", "a") as myfile:
myfile.write(x)
img = cv.QueryFrame(capture)
print("Taking image...")
cv.SaveImage('pic{:>05}.jpg'.format(i), img)
time.sleep(2)
y = ser2.readline()
with open("test2.txt", "a") as myfile:
myfile.write(y)
cv.WaitKey(1)
except:
continue
The camera is for taking continuous image frame and storing the latest 10 images in the current folder in each 2sec(Overwriting previous data). The datas from the arduino also logging into two separate text file. While running the code i am getting error messages as shown below.
pi#raspberrypi ~ $ sudo python accident.py
libv4l2: error setting pixformat: Device or resource busy
HIGHGUI ERROR: libv4l unable to ioctl S_FMT
libv4l2: error setting pixformat: Device or resource busy
libv4l1: error setting pixformat: Device or resource busy
HIGHGUI ERROR: libv4l unable to ioctl VIDIOCSPICT
Taking image...
Taking image...
Taking image...
^Z
[4]+ Stopped
While I searched for this problem , I found that, all the USB port of rasp-pi having the same serial port.
Can anybody help me to solve this issue...