I'm trying to choose a different from the default VideoCapture backend in Python. The code is the following:
cap = cv2.VideoCapture("my_video.avi", apiPreference=cv2.CAP_GSTREAMER)
But the capture is not opening:
cap.isOpened()
False
I checked the available backends using the following:
[cv2.videoio_registry.getBackendName(b) for b in cv2.videoio_registry.getBackends()]
['FFMPEG', 'GSTREAMER', 'INTEL_MFX', 'V4L2', 'CV_IMAGES', 'CV_MJPEG']
Querying cap.getBackendName() results in an error:
opencv-4.1.1/modules/videoio/src/cap.cpp:220: error: (-215:Assertion failed) api != 0 in function 'getBackendName'
I also tried to do the same with CAP_V4L2, and got the same result. The only option works is CAP_FFMPEG.
Why cannot I use a different backend?
OpenCV version: 4.1.1, Python 3.7. The backends were found during the build:
Video I/O:
-- DC1394: NO
-- FFMPEG: YES
-- avcodec: YES (57.107.100)
-- avformat: YES (57.83.100)
-- avutil: YES (55.78.100)
-- swscale: YES (4.8.100)
-- avresample: YES (3.7.0)
-- GStreamer: YES (1.14.5)
-- v4l/v4l2: YES (linux/videodev2.h)