SMIL

A W3C XML-based markup language for describing multimedia presentations that combine audio, video, text, images, and other media with precise temporal and spatial synchronization. SMIL is significant for accessibility because it includes a MediaAccessibility module that defines attributes for alternative content such as alt text, long descriptions, and reading order for assistive devices. While SMIL as a standalone format has been largely superseded by HTML5 video and modern streaming technologies, its concepts of synchronized media tracks and accessibility metadata influenced how captioning, audio description, and alternative content are handled in current multimedia standards.