Video Startup Time is a crucial metric in video analytics that measures the time it takes for a video to start playing after a viewer's intent to watch. It can be influenced by factors such as page load times, pre-roll ads, and pre-loading of videos. Mux offers solutions like splitting metrics into Video Startup Time and Aggregate Startup Time, providing detailed tracking, and offering a comprehensive overview of the viewer experience. Accurate measurement of this metric is essential for understanding audience engagement and optimizing video performance.