Build a Video Call App with Subtitles

This guide aims to bring the convenience of subtitles to video calls by leveraging Agora's Real-Time Transcription service, which transcribes spoken audio in real-time. The app uses a backend server to control the transcription process and ensures that only one instance of Real-Time Transcription runs within each channel. The `startTranscription` function is called after the join call method to initiate transcription as soon as the first user joins the channel, while the `stopTranscription` function is used to stop the transcription when the call ends. The app uses Protocol Buffers to decode and serialize the transcription data, which contains an array of words with transcribed sentences. The subtitle is updated in real-time using the `onStreamMessage` event, allowing users to view subtitles as they speak.