I am creating a video stream from my headless raspberry pi using usb camera and opencv.
Ubuntu 18.04 LTS
Raspi OS: Bullseye
USB Camera
gst syntax test on terminal:
gst-launch-1.0 v4l2src device=/dev/video0 ! videoconvert! videoscale ! video/x-raw, width=640, height=480 ! autovideosink -v
In OpenCV C++:
string pipeline;
pipeline = "v4l2src device=/dev/video0 ! videoconvert! videoscale ! video/x-raw, width=640, height=480 ! autovideosink -v";
cv::VideoCapture cap(pipeline, cv::CAP_GSTREAMER);
When I launch the pipeline from terminal it creates a window with by usb webcam feed. However when I try to use the same pipeline from c++ it throws this error:
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (734) open OpenCV | GStreamer warning: Error opening bin: syntax error
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (501) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created
terminate called after throwing an instance of 'std::invalid_argument'
what(): cannot predict with an empty OpenCV image
Aborted
What am i missing in the syntax in the code?
Edit: After some trials I could get the pipeline generated, with this:
pipeline = "v4l2src device=/dev/video0 ! videoconvert! video/x-raw, width=640, height=480 ! appsink";
and warning:
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (961) open OpenCV | GStreamer warning: Cannot query video position: status=0, value=-1, duration=-1
. . . some stuff for that frame . .
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (509) isPipelinePlaying OpenCV | GStreamer warning: unable to query pipeline state
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (1824) handleMessage OpenCV | GStreamer warning: Embedded video playback halted; module v4l2src0 reported: Could not read from resource.
When searched for it, I found this post. Which led to a bug report here and here.
I am using OpenCV 4.5, and I assume that bug would have been fixed by later version as it was reported for OpenCV 3.4.
