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Learn how to efficiently detect scene changes in videos using `FFmpeg`, while ignoring distracting elements like timers or overlays. Follow our step-by-step guide for better results in your video projects.
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Detecting Scene Changes in Video While Ignoring On-Screen Elements with FFmpeg

Are you working with a video file that contains on-screen elements, such as a timer, that complicate your ability to detect scene changes effectively? If you're looking to save images of each slide from a video lecture or presentation and need to ignore distractions present in the frame, you're in the right place! In this post, we’ll show you how to utilize FFmpeg to analyze only a specific portion of your video frame, allowing you to capture the essential elements while excluding unwanted changes.

Understanding the Problem

When you have a video consisting of slides, it's important to pick up changes between those slides without being misled by other movements or transitions—like a changing timer on the right side of the frame. If the threshold set for detecting scene changes is too low, any small change caused by the timer can lead to false positives. This is a common problem that can hinder the efficiency of slide extraction for lectures or presentations.

The Solution: An Optimized One-Command Approach

You might be tempted to create a complex script involving cropping and multiple analyses. However, there’s a more straightforward solution that you can implement in a single command using FFmpeg. Here’s how it works:

Step-by-Step Breakdown of the Command

The command outlined below simplifies the process of analyzing only a portion of the frame while retaining the full image for output.

[[See Video to Reveal this Text or Code Snippet]]

How This Works:

Split the Video: The command starts by creating two copies of the input video (split=2)—one of these ([full]) contains the full frame, and the other ([no_timer]) will be modified to ignore changes on the right side.

Draw the Box: The drawbox filter is applied to the [no_timer] copy. This effectively covers the right 25% of the frame (the area where the timer typically appears), allowing you to ignore any changes within this section. The box is painted solid black (drawbox=w=0.25*iw:h=ih:x=0.75*iw:y=0), which effectively masks the timer.

Select Scene Changes: Now that the distracting element is masked, the select filter analyzes the [no_timer] video for scene changes using the specified threshold (gt(scene,0.011)). It also records the timestamps of these changes to an output file.

Overlay the Frames: Finally, the command overlays the full unpainted frames with the selected frames, ensuring that only relevant slides are saved with the full background intact.

Result

This command efficiently analyses the left 75% of the frame for scene changes while ignoring any changes that occur on the right side. The scenes detected are saved as high-quality images (frames/img%03d.jpg) along with their respective timestamps in a .txt file. This approach is not only cleaner but also saves time and effort compared to scripting multiple steps.

Conclusion

Detecting scene changes while excluding certain on-screen elements does not have to be a complicated process. With FFmpeg, you can efficiently segment and analyze your video in a single command. This method allows you to maintain a high quality of output while simplifying your workflow. Whether you are working on academic projects or creative video editing, mastering these techniques can enhance your productivity and ensure you achieve the desired results without unnecessary distractions.

Give this command a try for your next project and see how it streamlines your video processing tasks!