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Merge pull request #28844 from 0lekW:videoio-image-seq-start

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Add CAP_PROP_IMAGE_SEQ_START #28844

Resolves https://github.com/opencv/opencv/issues/28843

New CAP_PROP_IMAGE_SEQ_START as an open only property for setting the first frame index when a VideoCap is opening with pattern, squashes test_images TODO.

`CAP_FFMPEG`: forwarded to the image2 demuxers "start_number" option.

`CAP_IMAGES`: Now a WithParams variant so the value reaches open() before probe runs, replaces 0 or 1 auto probe for sequence start.

Property is opt in so default behavior is not affected.  
Please note that G_STREAMER is not considered here as I think its out of scope, it already has a "start-index" property and its backend is driven by the pipeline strings rather then these printf patterns.

If an alternative solution is preferred that will not involve a new property or promoting CAP_IMAGES to a "WithParams" variant I don't mind implementing.  

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake
This commit is contained in:
Alex
2026-04-28 19:18:50 +12:00
committed by GitHub
parent 597c360b9d
commit 46ee0f7954
5 changed files with 80 additions and 12 deletions
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modules/videoio/include/opencv2/videoio.hpp
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@@ -210,6 +210,7 @@ enum VideoCaptureProperties {
CAP_PROP_N_THREADS = 70, //!< (**open-only**) Set the maximum number of threads to use. Use 0 to use as many threads as CPU cores (applicable for FFmpeg back-end only).
CAP_PROP_PTS = 71, //!< (read-only) FFmpeg back-end only - presentation timestamp of the most recently read frame using the FPS time base. e.g. fps = 25, VideoCapture::get(\ref CAP_PROP_PTS) = 3, presentation time = 3/25 seconds.
CAP_PROP_DTS_DELAY = 72, //!< (read-only) FFmpeg back-end only - maximum difference between presentation (pts) and decompression timestamps (dts) using FPS time base. e.g. delay is maximum when frame_num = 0, if true, VideoCapture::get(\ref CAP_PROP_PTS) = 0 and VideoCapture::get(\ref CAP_PROP_DTS_DELAY) = 2, dts = -2. Non zero values usually imply the stream is encoded using B-frames which are not decoded in presentation order.
CAP_PROP_IMAGE_SEQ_START = 73, //!< (**open-only**) Start number for image sequences opened with a printf-style pattern (e.g. `frame_%05d.dpx`). Sets the initial frame number and disables automatic first-frame detection. Applicable to \ref CAP_FFMPEG (passed as the image2 demuxer `start_number`) and \ref CAP_IMAGES backends. Default: not set (automatic detection).
#ifndef CV_DOXYGEN
CV__CAP_PROP_LATEST
#endif