What is the method for ensuring that videos commence playing solely when visible in the viewport?

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The method for ensuring that videos commence playing solely when visible in the viewport is by using Intersection Observer API in JavaScript. This API allows web developers to monitor when an element, such as a video, enters or exits the visible area of the viewport. By using this API, developers can add a callback function that runs when the video comes into view, allowing the video to begin playing only when it is visible in the viewport. This optimizes the website's performance by reducing unnecessary loading times and data usage.