I have problem with plying video file, why it is slow motion ?
How can I make it normal speed?
#include"opencv2/opencv.hpp"
using namespace cv;
int main(int, char**)
{
VideoCapture cap("eye.mp4");
// open the default camera
if (!cap.isOpened())
// check if we succeeded
return -1;
namedWindow("Video", 1);
while (1)
{
Mat frame;
cap >> frame;
imshow("Video", frame);
if (waitKey(10) == 'c')
break;
}
return 0;
}
VideoCapture isn't built for playback, it's just a way to grab frames from video file or camera. Other libraries that supports playback, such as GStreamer or Directshow, they set a clock that control the playback, so that it can be configured to play as fastest as possible or use the original framerate.
In your snippet, the interval between frames comes from the time it takes to read a frame and the waitKey(10). Try using waitKey(0), it should at least play faster. Ideally, you could use waitKey(1/fps).
Related
I have purchased an ELP-1MP2CAM001 which shows up as two webcam devices on Windows. If I open the Windwos default "Camera" app and Skype I can display the feeds from both the left and right camera at the same time. I don't think therefore it is a USB Bandwidth issue with two cameras coming into the same port
I'm using fairly standard code (shown below) to open both of these feeds and it works successfully if I use two standard Microsoft HD3000 webcams instead of the single stereo camera.
I've tried a range of numbers inside the cap2() arguments so I don't think it's hiding at number 10 or anything weird like that.
My questions are:
There must be some sort of on board hub for the ELP cameras, do I need to do something different in OpenCV?
Could it be that both frames are accessible through cap(0)? This seems unlikely to me.
This questions says I don't need to do anything special? but obviously I'm missing something.
Any help on this would be great.
Code:
#include <opencv2/opencv.hpp>
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
VideoCapture cap2(1); // open the default camera
cap.set(CV_CAP_PROP_FRAME_WIDTH, 240);
cap.set(CV_CAP_PROP_FRAME_HEIGHT, 120);
cap2.set(CV_CAP_PROP_FRAME_WIDTH, 240);
cap2.set(CV_CAP_PROP_FRAME_HEIGHT, 120);
if (!cap.isOpened()) // check if we succeeded
return -1;
if (!cap2.isOpened()) // check if we succeeded
return -1;
Mat frame;
Mat frame2;
namedWindow("Frame", 1);
namedWindow("Frame2", 1);
for (;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
imshow("Frame", frame);
Mat frame2;
cap2 >> frame2;
imshow("Frame2", frame2);
if (waitKey(30) >= 0) break; // Finish on "esc" key
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
I have the same camera as this, and I ran into the same problem before. Try change the order of your code as below:
VideoCapture cap(0);
cap.set(CV_CAP_PROP_FRAME_WIDTH, 240);
cap.set(CV_CAP_PROP_FRAME_HEIGHT, 120);
VideoCapture cap2(1);
cap2.set(CV_CAP_PROP_FRAME_WIDTH, 240);
cap2.set(CV_CAP_PROP_FRAME_HEIGHT, 120);
I think it's a problem with USB bandwidth. In your code, you opened two cameras in full resolution at the beginning, then you change the resolution of two cameras.
When you call VideoCapture cap(0); // open the default camera, cap has resolution 1280*720. cap already occupied the bandwidth. Thereby, VideoCapture cap2(1); won't open camera cap2 sucessfully.
Hope it helps.
According to VideoCapture documentation, there is a function called cv::VideoCapture::grab:
The primary use of the function is in multi-camera environments, especially when the cameras do not have hardware synchronization. That is, you call VideoCapture::grab() for each camera and after that call the slower method VideoCapture::retrieve() to decode and get frame from each camera
You can try that, with:
cap.grab();
cap.retrieve(...);
I'm using OpenCV 3.1, I try to run a simple code as the following one (main function):
cv::VideoCapture cam;
cv::Mat matTestingNumbers;
cam.open(0);
if (!cam.isOpened()) { printf("--(!)Error opening video capture\n"); return -1; }
while (cam.read(matTestingNumbers))
{
cv::imshow("matTestingNumbers", matTestingNumbers);
cv::waitKey(5000);
}
When I move the camera it seems that the code does not capture and show the current frame but shows all the captured frames from the previous position and only then from the new one.
So when I capture the wall it shows the correct frames (the wall itself) in the correct delay, but, when I twist the camera to my computer, I first see about 3 frames of the wall and only then the computer, it seems that the frames are stuck.
I've tried to use videoCapture.set() functions and set the FPS to 1, and I tried to switch the method of capturing to cam >> matTestingNumbers (and the rest of the main function according to this change) but nothing helped, I still got "stuck" frames.
BTW, These are the solutions I found on web.
What can I do to fix this problem?
Thank you, Dan.
EDIT:
I tried to retrieve frames as the following:
#include "opencv2/opencv.hpp"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat frame;
namedWindow("edges",1);
for(;;)
{
cap.grab();
if (waitKey(11) >= 0)
{
cap.retrieve(frame);
imshow("edges", frame);
}
}
return 0;
}
But, it gave the result (when I pointed the camera on one spot and pressed a key it showed one more of the previous frames that were captured of the other point).
It is just like you're trying to picture one person then another but when you picture the second you get the photo of the first person what doesn't make sense.
Then, I tried the following:
#include "opencv2/opencv.hpp"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat frame;
namedWindow("edges",1);
for(;;)
{
cap >> frame;
if (waitKey(33) >= 0)
imshow("edges", frame);
}
return 0;
}
And it worked as expected.
One of the problems is that you are not calling cv::waitKey(X) to properly freeze the window for X amount of milliseconds. Get rid of usleep()!
I am using console linux and I have a camera capture application. I need to capture an image without GUI(The camera should start and capture some images, save it to disk and close). The following code works well on my laptop but doesn't start on console. Any suggestions?
#include "cv.h"
#include "highgui.h"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
Mat frame;
namedWindow("feed",1);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
imshow("feed", frame);
imwrite("/home/zaif/output.png", frame);
if(waitKey(1) >= 0) break;
}
return 0;
}
After the release of OpenCV 2.4.6 there were bug fixes for video capture on Linux. Go straight to 2.4.6.2 and you should get the fixes. Specifically, this revision is probably the relevant fix for you, although there were a number of other revisions pertaining to video capture on android that might effect Linux compilation too.
I'm trying to set the camera parameters using the following codeand it is not working at all.
using namespace cv;
int main(int argc,char *argv[])
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
bool value = cap.set(CV_CAP_PROP_FRAME_WIDTH,10);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
imshow("frame", frame);
unsigned char *dad = (unsigned char*)frame.data;
if(waitKey(30) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
OpenCV tries to set this size directly in the camera, so it doesn't need to resize the frame.
The problem with this approach is that if your camera doesn't support this size natively, OpenCV will fail setting the value, leaving you the task to resize the frame after it is retrieved.
cap.set() seems to return the success of the function, I suggest you check it.
I recommend taking a look at another thread: how to change the capture resolution in OpenCV.
from opencv is using directshow for video capture. however, your camera only support a few of the resolution settings like, 480*320, 640*480, 720p, 1080p. if you set something else, it would not work at all.
if you want to check what kinds of resolution your camera support.
download the graphedt and check in the capture pin property.
the above code is not using for changing the camera parameters. I think it usu full for showing the video in your machine. May be this link is useful to you http://opencv.willowgarage.com/wiki/CameraCapture
I need a program to capture pictures from multiple webcams and save them automatically in Windows Vista. I got the basic code from this link. The code runs in Window XP, but when I tried using it on Vista it says "failed." Different errors pop up every time it is executed. Would it help if I used the SDK platform? Does anyone have any suggestions?
I can't test this on multiple webcams since I only have one, but I'm sure OpenCV2.0 should be able to handle it. Here's some sample code (I use Vista) with one webcam to get you started.
#include <cv.h>
#include <highgui.h>
using namespace cv;
int main()
{
// Start capturing on camera 0
VideoCapture cap(0);
if(!cap.isOpened()) return -1;
// This matrix will store the edges of the captured frame
Mat edges;
namedWindow("edges",1);
for(;;)
{
// Acquire the frame from cap into frame
Mat frame;
cap >> frame;
// Now, find the edges by converting to grayscale, blurring and then Canny edge detection
cvtColor(frame, edges, CV_BGR2GRAY);
GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
Canny(edges, edges, 0, 30, 3);
// Display the edges and the frame
imshow("edges", edges);
imshow("frame", frame);
// Terminate by pressing a key
if(waitKey(30) >= 0) break;
}
return 0;
}
Note:
The matrix edges is allocated during
the first frame processing and unless
the resolution will suddenly change,
the same buffer will be reused for
every next frame’s edge map.
As you can see, the code is quite clean and readable! I lifted this from the OpenCV 2.0 documentation (opencv.pdf).
The code not only displays the image from the webcam (under frame) but also does real-time edge detection! Here's a screenshot when I pointed the webcam at my monitor :)
screenshot http://img245.imageshack.us/img245/5014/scrq.png
If you want code to just display the frames from one camera:
#include <cv.h>
#include <highgui.h>
using namespace cv;
int main()
{
VideoCapture cap(0);
if(!cap.isOpened()) return -1;
for(;;)
{
Mat frame;
cap >> frame;
imshow("frame", frame);
if(waitKey(30) >= 0) break;
}
return 0;
}
If the program works with UAC off or when running administrator, make sure the place you choose to save the results are in writable places like the user's my documents folder. Generally speaking root folders and the program files folder is read only for normal users.