Symbl.ai is being used for live closed captioning in a telehealth starter kit, and the audio track is obtained from OpenTok Publisher using the OT.initPublisher() method, which returns a Publisher object that can be used to send audio to Symbl.ai via WebSockets. The Web Audio API is used to process the audio on the frontend, with nodes such as the AudioContext, source, script processor, and gain node being connected together to create an "audio boombox" that prepares the audio buffer for sending to Symbl.ai. A WebSocket connection is established with Symbl.ai using a unique meeting ID and access token, allowing for real-time insights and transcription of live meetings.