DTMF

DTMF (telephone-event, RFC 4733) is always negotiated on every endpoint. DTMF packets are never transcoded — they bypass the audio transcode pipeline and are forwarded directly between endpoints, with payload type remapping if needed.

Detection

When a remote endpoint sends DTMF via telephone-event RTP packets, rtpbridge automatically detects the completed digit and emits a dtmf event:

{
  "event": "dtmf",
  "data": {
    "endpoint_id": "...",
    "digit": "5",
    "duration_ms": 160
  }
}

Supported digits: 0-9, *, #, A-D.

Injection

endpoint.dtmf.inject

Send a DTMF digit into an endpoint's outbound stream.

{
  "id": "1",
  "method": "endpoint.dtmf.inject",
  "params": {
    "endpoint_id": "...",
    "digit": "5",
    "duration_ms": 160,
    "volume": 10
  }
}

Param	Type	Default	Description
endpoint_id	string	required	Target endpoint
digit	string	required	"0"-"9", "*", "#", "A"-"D"
duration_ms	u32	160	Duration in milliseconds (max 10,000)
volume	u8	10	Volume in dBm0 (0-63, RFC 4733 6-bit field)

The digit is sent as RFC 4733 telephone-event RTP packets with proper start/continuation/end signaling (3x redundant end packets per the RFC).

Forwarding

DTMF packets received from one endpoint are forwarded to all other endpoints in the session according to the routing table. If the source and destination endpoints negotiated different payload types for telephone-event, the PT is remapped automatically.