What VICIrecGateway does: stereo recording on a separate box

VICIrecGateway is designed to run on a stand-alone Asterisk server and record calls in Stereo recording. Instead of mixing both sides of a conversation into a single mono file, it writes carrier audio and dialer audio into separate channels — giving you clean, side-isolated recordings that are much easier to analyze, transcribe, or audit.

How the gateway intercepts calls

Calls are routed through the gateway box before reaching the dialer. The gateway runs agi-VICIrecGateway.agi, which sets two channel variables: CARRIER_FILENAME and DIALER_FILENAME. Those variables are then passed to MixMonitor with the r() and t() flags, which write the receive and transmit audio streams into separate file paths.

For inbound calls, the stereo-rec-inbound context in extensions.conf looks like this:

MixMonitor(,r(${CARRIER_FILENAME})t(${DIALER_FILENAME})S)

For outbound calls, the stereo-rec-outbound context swaps the r() and t() arguments so that CARRIER_FILENAME still captures the carrier (far) side and DIALER_FILENAME captures the dialer (near) side, keeping the channel mapping consistent regardless of call direction.

The header injection handler

To pass the recording ID back to the main dialer, the gateway uses a PJSIP header. A small handler context adds the X-VICIrecGatewayID header on outbound legs:

Set(PJSIP_HEADER(add,X-VICIrecGatewayID)=${VICIrecGatewayID})

This allows the dialer to associate the stereo recording files with the correct call record even though the recording happened on a different physical server.

Call flow through the gateway

sequenceDiagram
  participant Car as Carrier trunk
  participant GW as Gateway Asterisk
  participant Dial as Main VICIdial server
  Car->>GW: Call arrives on trunk
  GW->>GW: AGI sets CARRIER_FILENAME and DIALER_FILENAME
  GW->>GW: MixMonitor starts stereo capture
  GW->>Dial: Dial PJSIP with X-VICIrecGatewayID header
  Dial->>GW: Agent audio returns
  GW->>GW: Write carrier and dialer audio to separate channels
  GW->>GW: MixMonitor closes files on hangup

What you get in the recording files

The CARRIER_FILENAME file holds what the carrier sent into the system — the customer's voice on inbound calls. The DIALER_FILENAME file holds what the dialer transmitted — the agent's voice. A transcription or Voice analytics tool that understands stereo can then process each channel independently, which eliminates the crosstalk that plagues mono recordings.

**Heads up:** The gateway box must be configured with PJSIP and a working trunk back to your main dialer. Because all call audio passes through this server, its network latency and CPU headroom directly affect call quality. Size it as you would a production Asterisk server, not a minimal VM.

For the full recording background, see VICIdial call recording explained. To understand when a gateway server makes sense for your operation, see when to move recording onto a dedicated gateway server.

VICIfast can provision gateway recording servers as part of your deployment. See VICIfast pricing to find the right plan.