cudacodec::VideoReader::get returns incorect frame index for CAP_PROP_POS_FRAMES

[cudawarped]

System information (version)

• OpenCV => 4.8.0:
• Operating System / Platform => Windows 11
• Compiler => Visual Studio 2022

Detailed description

Due to the multi-threaded implementation of VideoReader, calling cudacodec::VideoReader::get() with CAP_PROP_POS_FRAMES will return the latest frame which has been input to the parser not the latest decoded frame as a user would expect.

The easiest fix would be to internally store the decoded frame index in VideoReaderImpl and intercept queries for CAP_PROP_POS_FRAMES in VideoReader::get before they are internally passed to VideoCapture.

Steps to reproduce

cv::Ptr<cv::cudacodec::VideoReader> reader = cv::cudacodec::createVideoReader(inputFile, {}, params);
double iFrame  = 0;
reader->get(cv::VideoCaptureProperties::CAP_PROP_POS_FRAMES, iFrame);

iFrame should be zero but it is guaranteed to be greater due to the fact that createVideoReader doesn't return until the decoder is initialized.

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc