The Video API broadcast sample app is a powerful tool for building live streaming applications on the web, utilizing the Vonage Video API's broadcasting capabilities to stream live video to multiple viewers. It is built using the Video API JavaScript SDK and allows developers to create real-time communications applications with features such as video chat, voice, and messaging. The app can scale to handle hundreds or thousands of viewers and provides customization options for developers to tailor the experience to their needs. It has roles defined for host, guest, viewer, and experience composer, allowing for flexibility in building live streaming applications.