GStreamer + OpenCV video processing problem

Question

I am planning on doing VideoCapture from OpenCV for video file stream/live rtsp stream. However, the VideoCapture has alot of latency when used in my program so i decided to use the gstreamer pipeline instead. For example, i used

VideoCapture capVideo("filesrc location=CarsDriving.mp4 ! qtdemux ! h264parse ! nvv4l2decoder ! nvvidconv ! video/x-raw, format=BGRx ! videoconvert ! video/x-raw, format=BGR ! appsink ", CAP_GSTREAMER);

My program is able to run but if i were to do something like

capVideo.get(CAP_PROP_FRAME_COUNT)

It always returns -1 because GStreamer has this warnings

[ WARN:0] global /home/nvidia/Downloads/opencv-4.4.0/source/modules/videoio/src/cap_gstreamer.cpp (898) open OpenCV | GStreamer warning: unable to query duration of stream [ WARN:0] global /home/nvidia/Downloads/opencv-4.4.0/source/modules/videoio/src/cap_gstreamer.cpp (935) open OpenCV | GStreamer warning: Cannot query video position: status=1, value=1, duration=-1

How do i get the frame count in opencv if i use gstreamer for the video pipeline? I need the framecount for exceptions and also video processing techniques.

Answer 1

This is a bug which @alekhin mentioned here and here. Also mentioned how to fix. After changing you should rebuild opencv.

Also you said:

However, the VideoCapture has alot of latency when used in my program so i decided to use the gstreamer pipeline instead.

rtsp cameras generaly streams as h264/h265 encoded data. If you are trying to decode that data via on CPU but not GPU, it will not give you much increasing about speed. Why don't you choose CAP_FFMPEG flag instead of CAP_GSTREAMER? CAP_FFMPEG will be faster than CAP_GSTREAMER