# Audio Recording & Streaming Architecture

This project implements an asynchronous and real-time audio messaging system using Phoenix Channels for binary streaming and Oban for background processing.

## 1. Components & Data Flow
- **Capture**: `AudioRecorder` JS Hook (`assets/js/hooks/audio_recorder.js`) utilizes the `MediaRecorder` API with `audio/webm;codecs=opus`.
- **Transport**: Binary chunks are transmitted via Phoenix Channels (`audio:lobby`).
- **Persistence**: The server appends incoming chunks to a `.webm` file located in `priv/static/uploads/`.
- **Finalization**: An `audio_end` event triggers an **Oban** job (`RiverConnect.Workers.ProcessRecording`) to verify the file and update the database status.
- **Serving**: Static audio files are exposed via a dedicated `Plug.Static` entry in `RiverConnectWeb.Endpoint`.

## 2. Channel Protocol (`AudioChannel`)
- **`audio_start`**: `%{"id" => id}`. Initializes the server-side recording state and creates the target file.
- **`audio_chunk`**: `{:binary, payload}`. Appends binary data to the file and broadcasts the chunk for real-time consumption.
- **`audio_end`**: `%{"duration_ms" => ms, "id" => id}`. Persists the `AudioMessage` record and enqueues the processing worker.

## 3. Real-time Streaming
- During an active recording session, the channel broadcasts `audio_chunk` events to all subscribers.
- Subscribed clients use `AudioContext.decodeAudioData` to process and play the binary stream with minimal latency.

## 4. Database Schema (`AudioMessage`)
- `user_id`: Identifies the sender (Guest or Authenticated).
- `file_path`: Relative URL to the static resource.
- `duration_ms`: Integer representing the length of the audio.
- `status`: State machine values (`"processing"`, `"ready"`).
- **Note**: The schema must `@derive {Jason.Encoder, ...}` for binary serialization over the socket.

## 5. Environment & Infrastructure
- **Windows Support**: `mix` commands in background processes may require explicit PATH configuration for Erlang/Elixir binaries.
- **Static Configuration**: Dynamic directories in `priv/static` require explicit inclusion in the `Endpoint` configuration to be served correctly.

## 6. Implementation Notes
- **Server Restarts**: Modifications to `endpoint.ex` or `UserSocket` require a server restart to take effect.
- **Hardware Access**: Web-based recording requires secure context (HTTPS/Localhost) and explicit browser microphone permissions.
- **Latency Management**: Real-time playback relies on prompt chunk processing; production environments may require a jitter buffer for consistency.