Accessing gstreamer timestamp from python

[Michael Gruner]

Hello Letty

The limitation here is OpenCV rather than Python. The way the GStreamer VideoCapture works is that it will make a copy of the GstBuffer’s data into a newly allocated cv::Mat. As such, once you do a cap.read(), you don’t have access to the GstBuffer nor its timestamp anymore.

Having said that, if you’re looking for a workaround, here’s the precise line that makes the copy:
https://github.com/opencv/opencv/blob/125b9f60574d40cbd59f5927646c385bba96f526/modules/videoio/src/cap_gstreamer.cpp#L1937

Maybe you can read the timestamp from there and embed this info in the first bytes of the image. Not the prettiest solution though ¯\_(ツ)_/¯.

You’ll need to build OpenCV from source, here are some instructions:
https://developer.ridgerun.com/wiki/index.php?title=Compiling_OpenCV_from_Source

Make sure to enable the GStreamer option.

Michael
www.ridgerun.com

> On 2 Apr 2021, at 04:26, Letty <letizia.mariotti at gmail.com> wrote:
> 
> Apologie but my code didn't show up. Here it is
> 
> This is my gstreamer pipeline:
> 
> gst_in =  ('nvarguscamerasrc sensor-id=0 ! '
>    'video/x-raw(memory:NVMM), height=1080, width=1920,
> framerate=(fraction)30/1, format=NV12 ! '
>    'nvvidconv ! video/x-raw, height=1080, width=1920, format=BGRx ! '
>    'videoconvert ! video/x-raw, format=BGR ! '
>    'appsink')
> 
> which then I call through VideoCapture
> 
> cap = cv2.VideoCapture(gst_in, cv2.CAP_GSTREAMER)
> 
> while True:
>    ret, frame = cap.read()
> 
> 
> 
> --
> Sent from: http://gstreamer-devel.966125.n4.nabble.com/
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