How to call OpenCV VideoCapture() with params (third) argument in Python

Question

Using OpenCV (4.5.4) on Ubuntu (Ubuntu Server 20.04.3 LTS (RPi 2/3/4/400) / 32-bit) in Python (3.9.7). Generally successful, but I do not know how to pass the third argument to the VideoCapture() call that has a C++ interface given as:

cv::VideoCapture::VideoCapture (
   const String & filename,
   int apiPreference,
   const std::vector< int > & params 
)

Specified here:

OpenCV Video I/O VideoCapture class

Current code looks like:

import cv2
cap = cv2.VideoCapture('/dev/video0', cv2.CAP_FFMPEG)

Which works fine, but I want to pass the third argument to the call so that I can set video parameters. I've tried passing the third argument as a list of tuples [(a1,v1), (a2,v2)] and as a dict {a1:v1, a2:v2} but neither works.

I can't find any examples in a lot of searching...

Dick Fox · Accepted Answer · 2021-12-07 01:16:30Z

1

Try like this:

cap = cv2.VideoCapture('/dev/video0', cv2.CAP_FFMPEG, (a1, v1, a2, v2))

Here's the relevant bit from the docs you linked:

The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...).

answered Dec 7, 2021 at 1:16

Dick Fox

2,9942 gold badges16 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

robohobo Over a year ago

Thank you, I had tried that but convinced myself it was not working. It does in fact seem to pass the parameters to the call. Remaining problem is that I still cannot properly open the capture device using FFMPEG UNLESS I set environment variables like this: export OPENCV_FFMPEG_CAPTURE_OPTIONS="input_format;rawvideo|video_size;640x480". Then all is well, but that really defeats the purpose of passing in video parameters as above.

Collectives™ on Stack Overflow

How to call OpenCV VideoCapture() with params (third) argument in Python

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related