@seydx/rtsp / BackchannelInfo

Interface: BackchannelInfo

Defined in: types.ts:151

Describes the upstream's talkback (ONVIF backchannel) audio format.

Present only when the upstream accepts audio sent back to it (for example an RTSP camera that exposes an ONVIF backchannel). The codec and clock fields describe exactly what the upstream expects to receive, so a sink can encode or repackage viewer audio into a compatible stream before forwarding it.

Example

import { Source, supportsBackchannel } from '@seydx/rtsp';

if (supportsBackchannel(source) && source.backchannel) {
  const { codec, clockRate, channels } = source.backchannel;
  console.log(`talkback expects ${codec} @ ${clockRate}Hz x${channels}`);
}

See

BackchannelSource For the source capability that exposes this

Properties

channels

channels: number

Defined in: types.ts:198

Number of audio channels in the backchannel.

Typically 1 for the mono talkback streams cameras expect.

---

clockRate

clockRate: number

Defined in: types.ts:191

RTP clock rate of the backchannel, in Hz.

Used to compute RTP timestamps for outbound packets at the rate the upstream expects (e.g. 8000 for G.711, 48000 for Opus).

---

codec

codec: string

Defined in: types.ts:166

Lower-case codec name expected by the upstream.

Examples include pcm_mulaw, pcm_alaw, and aac. Reported in the canonical FFmpeg short-name form.

---

codecId?

optional codecId?: AVCodecID

Defined in: types.ts:175

node-av AVCodecID for the backchannel codec.

Provided so a transcoder can construct a matching encoder when the viewer audio must be converted into the upstream's expected format. Absent when the id is not available.

---

payloadType

payloadType: number

Defined in: types.ts:183

RTP payload type advertised for the backchannel.

The dynamic or static payload type number that must be stamped on outbound RTP packets so the upstream associates them with the backchannel stream.

---

streamIndex

streamIndex: number

Defined in: types.ts:158

Upstream stream index used to send packets back.

Identifies the backchannel stream on the upstream connection (e.g. the RTSP track to which outbound RTP packets are written).