If the camera stacking mode is used (many frames with a slight focus shift, which the camera does automatically), then, in many cases, such series have a common series identifier (BurstID, ImageSequenceID, etc).In such a case, exiftool is a utility that will help solve the problem with one command: https://exiftool.org/
If you want to rely only on the time delta between frames, you may need some more advanced scripting (on top of exiftool or not).
In any case, the logic you describe is outside the FastRawViewer's scope
If the camera stacking mode
If the camera stacking mode is used (many frames with a slight focus shift, which the camera does automatically), then, in many cases, such series have a common series identifier (BurstID, ImageSequenceID, etc). In such a case, exiftool is a utility that will help solve the problem with one command: https://exiftool.org/
If you want to rely only on the time delta between frames, you may need some more advanced scripting (on top of exiftool or not).
In any case, the logic you describe is outside the FastRawViewer's scope
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Alex Tutubalin/FastRawViewer team