ITVDesk supports the ONVIF audio back channel specification

ITVDesk now supports the ONVIF audio back channel specification, leveraging the RTSP protocol to facilitate bidirectional audio streams. This advanced functionality allows clients to not only receive audio and video streams from their surveillance cameras but also send audio back to the camera or the surveillance system. Here’s how it works within our application:

### Understanding the ONVIF Audio Back Channel

The audio back channel feature utilizes RTSP, as outlined in RFC 2326, enhanced with specific feature-tags indicating the initiation of a backchannel connection. This is particularly useful for devices supporting two-way audio or metadata connections, enabling users to communicate directly through the surveillance system.

### Implementing RTSP Require-Tag in ITVDesk

1. **RTSP Require-Tag Utilization**: ITVDesk incorporates additional header objects to the RTSP standard for extending functionality. The "Require" tag is a critical addition, signaling the support for backchannel features. When setting up a connection that includes audio output capabilities, ITVDesk recognizes and processes the backchannel tag (`www.onvif.org/ver20/backchannel`) as specified in the RTSP requests.

### Setting up a Bi-Directional Connection

2. **Bi-Directional Connection Setup**:
   - When initiating a connection, ITVDesk users can include the feature tag within their DESCRIBE request, indicating the establishment of a bidirectional data connection.
   - Upon receiving a request with the correct "Require" tag, ITVDesk configures an additional media stream within its SDP (Session Description Protocol) file, adhering to the specified Media Profile. This setup ensures the inclusion of both sending and receiving media directions, facilitating two-way audio communication.
   - In instances where the backchannel feature tag is unrecognized or unsupported, ITVDesk responds with a standard RTSP error code (551 Option not supported), guiding users to proceed without the backchannel setup.

### Session Description and Codec Selection

- ITVDesk's SDP file meticulously details the session parameters, including the direction of media data (`sendonly` for client-to-server streams and `recvonly` for server-to-client streams) and the supported decoding codecs. This comprehensive description enables the server (ITVDesk) to correctly interpret and process the audio streams sent by the client.

By integrating the ONVIF audio back channel specification, ITVDesk enhances its surveillance capabilities, offering users a robust platform for not only monitoring but also interacting with their environment through two-way audio communications. This feature underscores ITVDesk's commitment to providing advanced surveillance solutions that meet the evolving needs of its users.