How can I detect a dropped frame in OpenCV? Right now I am doing a check like the following:
int main() {
VideoCapture cap(-1);
if (!cap.isOpened()) {
cout << "Webcam is not open." << endl;
return -1;
}
Mat frame;
while (true) {
cap.read(frame);
if (!frame.empty()) {
imshow("frame", frame);
}
else {
cout << "No captured frame" << endl;
break;
}
}
}
But I still get messages saying "Camera frame dropped!" without my "No captured frame" message. What conditions result in the camera frame being dropped/how can I check for those conditions?
You can use this opencv function cap.get(CV_CAP_PROP_POS_MSEC) to obtain the presentation timestamp of a videoframe. This function returns an integer in multiples of time interval. If any frame drop, the timestamp would have skipped to (N+2)*time_interval instead of (N+1)*time_interval where N is your current frame number.
Related
I'm attempting to read an Azure Kinect recording and save images from the frames. But, it is not possible to set the color_format, which causes problems when using imwrite.
I have read the recording documentation here: https://learn.microsoft.com/en-us/azure/Kinect-dk/azure-kinect-recorder.
By default, the format seems to be K4A_IMAGE_FORMAT_COLOR_MJPG. But I am unsure what parameter to pass in when creating the material. For BGRA32 it is CV_8UC4 and for depth images it is CV_16U.
I assume there are two ways to solve this problem, either by setting the color_format or figuring out what parameter is correct for the default format made by the recording.
You can access the rgb with OpenCV as if it were a normal webcam:
VideoCapture cap(0); // open the default camera
cap.set(CV_CAP_PROP_FRAME_WIDTH, 3840);
cap.set(CV_CAP_PROP_FRAME_HEIGHT, 2160);
if (!cap.isOpened()) // check if we succeeded
return -1;
Mat frame, img;
for (;;)
{
cap >> frame; // get a new frame from camera
cout << frame.cols << " x " << frame.rows << endl;
resize(frame, img, Size(), 0.25, 0.25);
imshow("frame", img);
if (waitKey(30) >= 0) break;
}
No k4a function is called, no need to set the color format.
If you want to use their SDK with jpeg format, they provide a function in one of their sample codes:
long WriteToFile(const char *fileName, void *buffer, size_t bufferSize)
{
cout << bufferSize << endl;
assert(buffer != NULL);
std::ofstream hFile;
hFile.open(fileName, std::ios::out | std::ios::trunc | std::ios::binary);
if (hFile.is_open())
{
hFile.write((char *)buffer, static_cast<std::streamsize>(bufferSize));
hFile.close();
}
std::cout << "[Streaming Service] Color frame is stored in " << fileName << std::endl;
return 0;
}
You just call:
image = k4a_capture_get_color_image(capture);
WriteToFile("color.jpg", k4a_image_get_buffer(image), k4a_image_get_size(image));
Finally, you can set the format to RGBA32:
config.color_format = K4A_IMAGE_FORMAT_COLOR_BGRA32;
and convert it into a OpenCV Mat:
color_image = k4a_capture_get_color_image(capture);
if (color_image)
{
uint8_t* buffer = k4a_image_get_buffer(color_image); // get raw buffer
cv::Mat colorMat(Hrgb, Wrgb, CV_8UC4, (void*)buffer, cv::Mat::AUTO_STEP);
//do something with colorMat
k4a_image_release(color_image);
}
More details on the last option here: How to convert k4a_image_t to opencv matrix? (Azure Kinect Sensor SDK)
The data is slightly better with the last solution, but the buffer is significantly larger (33M vs ~1.5M) for 3840x2160.
This program captures video until I press Esc. But I need to modify this program and capture video for 30s.
After recording the video it plays very fast and the video length reduces. I tried to add waitKey at the end, but it still doesn't work. After recording the video length should be the same. How can I do that? Any suggestions?
int main( int argc, const char** argv )
{
using namespace std;
using namespace cv;
VideoCapture cap(0);
while(!(cap.isOpened() && cap.grab()))
{
cout << "Camera not ready" << endl;
}
VideoWriter Writer("D:/MyVideo.avi", CV_FOURCC('P','I','M','1'),20,Size(640,480), true);
while (waitKey(30)!= 27)
{
Mat frame;
cap >> frame;
Writer.write(frame);
imshow("D:/MyVideo", frame);
}
}
int64 t0 = cv::getTickCount();
while (waitKey(30)!= 27)
{
Mat frame;
cap >> frame; // read a new frame from video
Writer.write(frame); //writer the frame into the file
double t = (cv::getTickCount() - t0) / cv::getTickFrequency();
if (t > 30)
break;
...
// now, we need to adjust to the desired framerate of 20fps,
// so we need to sleep for 1000/20 = 50 milliseconds
// either have a window, and use waitKey():
// imshow("lalala", frame);
// waitKey(50);
// or just sleep(), unfortunately system dependant ;(
// win:
// Sleep(50);
// linux, etc.:
// usleep(50);
}
I am using opencv 2.4.7, windows 7 and vc++2010 to stream mjpeg from a foscam ip camera. cap.isOpened is not null but only the first frame is displayed and breaks from loop in the second round. this is part of the code I am using:
VideoCapture cap("http://IP:PORT/cgi-bin/CGIProxy.fcgi?cmd=snapPicture2&usr=X&pwd=Y&.mjpg"); // open the video file for reading
if ( !cap.isOpened() ) // if not success, exit program
{
std::cout << "Cannot open the video file" << std::endl;
return -1;
}
cap.set(CV_CAP_PROP_POS_MSEC, 30); //start the video at 300ms
double fps = cap.get(CV_CAP_PROP_FPS); //get the frames per seconds of the video
std::cout << "Frame per seconds : " << fps << std::endl;
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
int cnt=0;
Mat frame;
for(;;)
{
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
std::cout << "Cannot read the frame from video file" << std::endl;
break;
}
imshow("MyVideo", frame); //show the frame in "MyVideo" window
if(waitKey(33) == 27) //wait for 'esc' key press for 30 ms. If 'esc' key is pressed, break loop
{
std::cout << "esc key is pressed by user" << std::endl;
break;
}
}
}
I appreciate any help in advance.
look at your url:
"IP:PORT/cgi-bin/CGIProxy.fcgi?cmd=snapPicture2&usr=X&pwd=Y&.mjpg"
snapPicture2 looks suspicious, no ?
i'm pretty sure, there's no problem with your opencv code,
it's more like the url you choose only retrieves 1 frame
please lookup your manual for the correct stream url
http://www.ispyconnect.com/man.aspx?n=foscam
I am reading a avi file, and do some background subtrcation work. The wierd thing is when I use cvRetrieveFrame, I got a strange image, like below:
origin:
cvRetrieveFrame returns:
I don't know what's the problem. Here is my code snippet.
CvCapture* readerAvi = cvCaptureFromAVI( filename.c_str() );
if(readerAvi == NULL)
{
std::cerr << "Could not open AVI file." << std::endl;
return 0;
}
// retrieve information about AVI file
cvQueryFrame(readerAvi); //....get some information, width, height, ....
// grad next frame from input video stream
if(!cvGrabFrame(readerAvi))
{
std::cerr << "Could not grab AVI frame." << std::endl;
return 0;
}
frame_data = cvRetrieveFrame(readerAvi);
I run a program similar to the one in this question: https://stackoverflow.com/a/8719192/26070
#include <opencv/highgui.h>
#include <iostream>
/** #function main */
int main( int argc, char** argv )
{
cv::VideoCapture vcap;
cv::Mat image;
const std::string videoStreamAddress = "rtsp://192.0.0.1:8081/live.sdp";
//open the video stream and make sure it's opened
if(!vcap.open(videoStreamAddress)) {
std::cout << "Error opening video stream or file" << std::endl;
return -1;
}
for(;;) {
if(!vcap.read(image)) {
std::cout << "No frame" << std::endl;
cv::waitKey(500);
} else {
cv::imshow("Output Window", image);
}
if(cv::waitKey(1) >= 0) break;
}
}
The program runs fine for a certain amount of time (about one minute or so) and then the call to read() (method from cv::VideoCapture) always returns false.
The output is as follows:
[mpeg4 # 00da27a0] ac-tex damaged at 22 7
[mpeg4 # 00da27a0] Error at MB: 309
No frame
No frame
No frame
Note: the first two lines are not always present.
So, how can I determine what the root of the problem is?