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I'm posting this because i was already searching the web trying to find some explenation for the errors caused but didn't find any.

So I'm trying to shoot a timelapse of a growing plant from 4 different angles. I have 4 webcams (Logitech B525) attached to my raspberry Pi 3. Once an hour all 4 cams should shoot a time synced frame as narrow and accurate as possible.

After running smoothly doing what it should, sometimes for minutes sometimes for hours, the cameras attached are not found anymore by V4L or putting out corrupted information. The cameras producing errors are random, so no bad usb ports, no broken cables. After a while the failing camera starts working again then another is failing, this continues until all cameras fail and the program stops.

Here an example of the Error Outputs

My programmed output of the saving period:

cam 1 attached
cam 2 attached
cam 3 attached
cam 4 attached
18-10-23_10-00-00
saving file of frame 4.. '../cam4/cam4_image_18-10-23_10-00-00.jpg'
18-10-23_10-00-01
saving file of frame 3.. '../cam3/cam3_image_18-10-23_10-00-01.jpg'
18-10-23_10-00-02
saving file of frame 2..'../cam2/cam2_image_18-10-23_10-00-02.jpg'
18-10-23_10-00-02
saving file of frame 1.. '../cam1/cam1_image_18-10-23_10-00-02.jpg'
waiting for next capture!

Then Errors occur:

libv4l2: error setting pixformat: Input-/Output Error
VIDEOIO ERROR: libv4l unable to ioctl S_FMT
libv4l2: error setting pixformat: Input-/Output Error
libv4l1: error setting pixformat: Input-/Output Error
libv4l2: error setting pixformat: Input-/Output Error
libv4l1: error setting pixformat: Input-/Output Error
VIDEOIO ERROR: libv4l unable to ioctl VIDIOCSPICT

cam 1 not attached
cam 2 attached
VIDEOIO ERROR: V4L: device /dev/video2: Unable to query number of channels
cam 3 not attached
libv4l2: error setting pixformat: Input-/Output Error
VIDEOIO ERROR: libv4l unable to ioctl S_FMT
libv4l2: error setting pixformat: Input-/Output Error
libv4l1: error setting pixformat: Input-/Output Error
libv4l2: error setting pixformat: Input-/Output Error
libv4l1: error setting pixformat: Input-/Output Error
VIDEOIO ERROR: libv4l unable to ioctl VIDIOCSPICT

cam 4 not attached
sh: 1: reboot: not found
libv4l2: error setting pixformat: Input-/Output Error
VIDEOIO ERROR: libv4l unable to ioctl S_FMT
libv4l2: error setting pixformat: Input-/Output Error
libv4l1: error setting pixformat: Input-/Output Error
libv4l2: error setting pixformat: Input-/Output Error
libv4l1: error setting pixformat: Input-/Output Error
VIDEOIO ERROR: libv4l unable to ioctl VIDIOCSPICT


cam 1 attached
cam 2 attached
cam 3 attached
VIDEOIO ERROR: V4L: device /dev/video3: Unable to query number of channels
cam 4 not attached

The Cameras never disconnect and are always present within the device folder /dev/videoX all the time, i guess it is ok to assume it's not a power issue.

my part of the code causing the errors is the switch part repeating over and over again with a 5 seconds delay. My guess is a USB bandwith issue since the raspberry has only one USB 2.0 bus split up into 4 ports. I tried adding more time between closing and opening a capture again but nothing really helped. Am i missing something?

Here's my Code:

                switch(4)
                {
                    case 4:
                    {
                        VideoCapture cap4(3);
                        if(!cap4.isOpened())
                        {
                            cout<<"cam 4 not functional or attached!"<<endl;
                        }
                        else
                        {
                            //cap4.set(5, 30); //5=FPS settings
                            //cap4.set(38, 3); //38=Buffersize settings, Frames saved in Buffer
                            cap4.set(3,1280);//3=Width, Pixelcount
                            cap4.set(4,720); //4=Height, Pixelcount
                            Mat frame4;
                            cap4 >> frame4; // get a new frame from camera
                            waitKey(30); //wait for 2 Frames
                            cap4.release();
                            imshow("camera_4", frame4);                             

                            if(frame4.empty())
                            {
                                cerr<<"Something is wrong with the camera 4, could not get frame 4!"<<endl;
                            }
                            else
                            {
                                try
                                {
                                    if(save_next_file)
                                    {
                                        string name4 = "../cam4/cam4_image_"+currentDateTime()+".jpg";
                                        cout<<"saving file of frame 4.. '"<<name4<<"'"<<endl;
                                        imwrite(name4.c_str(),frame4);
                                        waitKey(30);
                                        gettimeofday(&last_save, NULL); //reset the time interval
                                    }
                                }   
                                catch(cv::Exception e)
                                {
                                    cout<<"error saving frame 4. >__<"<<endl;
                                }
                            }
                        }
                    }


                    case 3:
                    {
                        VideoCapture cap3(2);
                        if(!cap3.isOpened())
                        {
                            cout<<"cam 3 not functional or attached!"<<endl;
                        }
                        else
                        {
                            //cap3.set(5, 30); //5=FPS settings
                            //cap3.set(38, 3); //38=Buffersize settings, Frames saved in Buffer
                            cap3.set(3,1280);//3=Width, Pixelcount
                            cap3.set(4,720); //4=Height, Pixelcount
                            Mat frame3;
                            cap3 >> frame3; // get a new frame from camera
                            waitKey(30); //wait for 2 Frames
                            cap3.release();
                            imshow("camera_3", frame3);

                            if(frame3.empty())
                            {
                                cerr<<"Something is wrong with the camrea 3, could not get frame 3. >__<"<<endl;
                            }
                            else
                            {                   
                                try
                                {
                                    if(save_next_file)
                                    {
                                        string name3 = "../cam3/cam3_image_"+currentDateTime()+".jpg";
                                        cout<<"saving file of frame 3.. '"<<name3<<"'"<<endl;
                                        imwrite(name3.c_str(),frame3);
                                        waitKey(25);
                                        gettimeofday(&last_save, NULL); //reset the time interval
                                    }
                                }       
                                catch(cv::Exception e)
                                {
                                    cout<<"error saving frame 3."<<endl;
                                }
                            }
                        }
                    }


                    case 2:
                    {
                        VideoCapture cap2(1);
                        if(!cap2.isOpened())
                        {
                            cout<<"cam 2 not functional or attached!"<<endl;
                        }
                        else
                        {
                            //cap2.set(5, 30); //5=FPS settings
                            //cap2.set(38, 3); //38=Buffersize settings, Frames saved in Buffer
                            cap2.set(3,1280);//3=Width, Pixelcount
                            cap2.set(4,720); //4=Height, Pixelcount
                            Mat frame2;
                            cap2 >> frame2; // get a new frame from camera
                            waitKey(30); //wait for 2 Frames
                            cap2.release();
                            imshow("camera_2", frame2);

                            if(frame2.empty())
                            {
                                cerr << "Something is wrong with the camera 2, could not get frame 2!" << endl;
                            }
                            else
                            {
                                try
                                {
                                    if(save_next_file)
                                    {
                                        string name2 = "../cam2/cam2_image_"+currentDateTime()+".jpg";
                                        cout<<"saving file of frame 2..'"<<name2<<"'"<<endl;
                                        imwrite(name2.c_str(),frame2);
                                        waitKey(25);
                                        gettimeofday(&last_save, NULL); //reset the time interval
                                    }
                                }
                                catch(cv::Exception e)
                                {
                                    cout<<"error saving frame 2. >__<"<<endl;
                                }
                            }
                        }
                    }


                    case 1:
                    {
                        VideoCapture cap1(0);
                        if(cap1.isOpened())
                        if(!cap1.isOpened())
                        {
                            cout<<"cam 1 not functional or attached!"<<endl;
                        }
                        else
                        {
                            //cap1.set(5, 30); //5=FPS settings
                            //cap1.set(38, 3); //38=Buffersize settings, Frames saved in Buffer
                            cap1.set(3,1280);//3=Width, Pixelcount
                            cap1.set(4,720); //4=Height, Pixelcount
                            Mat frame1;
                            cap1 >> frame1; // get a new frame from camera
                            waitKey(30); //wait for 2 Frames
                            cap1.release();
                            imshow("camera_1", frame1);

                            if(frame1.empty())
                            {
                                cerr << "Something is wrong with camera 1, could not get frame 1!" << endl;
                            }
                            else
                            {
                                try
                                {
                                    if(save_next_file)
                                    {
                                        string name1 = "../cam1/cam1_image_"+currentDateTime()+".jpg";
                                        cout<<"saving file of frame 1.. '"<<name1<<"'"<<endl;
                                        imwrite(name1.c_str(),frame1);
                                        waitKey(25);
                                        gettimeofday(&last_save, NULL); //reset the time interval
                                    }
                                }
                                catch(cv::Exception e)
                                {
                                    cout<<"error saving frame 1!"<<endl;
                                }
                            }
                        }
                    }       
                }
eALduderino
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  • I am having the same problem ... have you solved it ? – Steven Nov 06 '18 at 22:43
  • Hey Steven, unfortunately no. I had a solution by adding more sleep time between each shot during the capture period. This was before when I was using python. Adding more time between the shots isn't an option for me though. I need the shots to be as close to each other as possible. – eALduderino Nov 07 '18 at 23:07
  • Thanks for your feedback. In my case, I am using the C++ openCV lib. I realised that the problem doesn't alwasys occurs. It works about 1 time over 5. Have you tried to play with v4l2-ctl --set-fmt-video to try other video formats ? – Steven Nov 08 '18 at 07:09
  • actually I tried, but still same errors. the errors also occur when trying to imshow directly more than one camera. I guess it's usb bandwidth related and maybe also response time related, meaning that the cameras need more time to start and end a capture before another camera starts a capture :/ :? – eALduderino Nov 08 '18 at 10:50
  • Before using OpenCV I tried Qt with QCamera and didnt have any device opening problem. If you just need to take simultaneous pictures, this can probably do the trick for you. – Steven Nov 09 '18 at 06:36

2 Answers2

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Just found this post : https://stackoverflow.com/a/53472812/3643138 Try to open your device with a file name instead of an index ! This did the trick for me !

Steven
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So guys late Update. I found out last year it was all Raspberry Pi related. USB Bandwith and The Raspberry pi 3B+ are simply underpowered. I ran the same codes I used on my Raspberry also on my computer and had no issues there. I was even able to run 4 camera streams simultaneously while multi-threading the tasks. The Pi can handle one low res webcam at once but as soon another is going to be used, simultaneously streaming or even single image captures won't work.

eALduderino
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