Merge pull request #28176 from shahkarnav115-beep:docs-animation-frame-duration

Docs(imgcodecs): clarify animation frame duration units #28176

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- [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
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Docs-only change. No code or tests affected.

doc/tutorials/app/animations.markdown

@@ -67,6 +67,9 @@ Explanation
 
    Each frame in the `animation.frames` vector can be displayed as a standalone image. This loop iterates through each frame, displaying it in a window with a short delay to simulate the animation.
 
+> **Note:** Frame durations in `cv::Animation` are expressed in milliseconds.
+> When displaying frames manually using `cv::waitKey`, make sure to use the corresponding duration value to preserve the original animation timing.
+
 @add_toggle_cpp
 @snippet cpp/tutorial_code/imgcodecs/animations.cpp show_animation
 @end_toggle