ONVIF plugin: Axis cameras (A8004-VE) talkback fails - no ONVIF Profile T backchannel, but Axis VAPIX transmit.cgi / simplex=receiver RTSP available as fallback

[patikoija]

Summary

Axis A8004-VE doorbell does not support ONVIF Profile T backchannel (www.onvif.org/ver20/backchannel). The camera's GStreamer RTSP server returns 551 Option not supported when the DESCRIBE request includes Require: www.onvif.org/ver20/backchannel. This is a firmware limitation (firmware 1.65.14, latest available).

One-way audio (doorbell mic → phone speaker) works correctly after adding audio encoder to the ONVIF H264 profile. Only the talkback direction (phone mic → doorbell speaker) is broken.

Camera Details

• Model: Axis A8004-VE Network Video Door Station
• Firmware: 1.65.14 (Dec 19 2024, latest)
• ONVIF Services: Media 1 only (http://www.onvif.org/ver10/media/wsdl) — no Media 2 / Profile T
• Audio mode: Full duplex (root.Audio.DuplexMode=full)

What the camera DOES support for talkback

1. VAPIX HTTP audio push (tested — endpoint accepts connections):

   POST http://camera/axis-cgi/audio/transmit.cgi
   Content-Type: audio/basic  (G.711 mu-law) or audio/mpeg4-generic (AAC)
   [streaming audio body]
   

2. Axis RTSP simplex=receiver (tested — DESCRIBE returns SDP):

   rtsp://camera/axis-media/media.amp?simplex=receiver&audio=1&video=0
   

   Requires ANNOUNCE→SETUP→RECORD flow (not DESCRIBE→SETUP→PLAY)

Suggested Fix

When checkIntercom() fails with "ONVIF audio backchannel not found", fall back to:

1. VAPIX HTTP POST (for Axis cameras — detectable by manufacturer in ONVIF device info)
2. Or: a configurable user-specified talkback URL / mechanism in the ONVIF plugin Advanced settings

A plugin setting like "Two-Way Audio URL override" (similar to how some NVRs allow specifying a custom talkback RTSP URL) would be a general solution for cameras that support non-standard talkback methods.

Logs

[doorbell] Require: www.onvif.org/ver20/backchannel
[doorbell] Unsupported: www.onvif.org/ver20/backchannel

Camera RTSP response:

RTSP/1.0 551 Option not supported
Unsupported: www.onvif.org/ver20/backchannel
Server: GStreamer RTSP server

[patikoija]

Resolved this ourselves with a custom patch to the ONVIF plugin.

Root cause: Axis A8004-VE has no ONVIF Profile T / backchannel support at all (firmware limitation). The RTSP server returns 551 unconditionally.

Solution: Patched main.nodejs.js in the ONVIF plugin to catch the 551 error and fall back to Axis VAPIX HTTP audio push (/axis-cgi/audio/transmit.cgi). ffmpeg reads from the Scrypted RTSP relay (Opus 48kHz stereo) and POSTs G.711 mu-law 8kHz mono to the VAPIX endpoint.

One-way audio (doorbell mic → phone) works via the standard ONVIF RTSP stream after adding an audio encoder to the H264 profile.

For anyone hitting this with other Axis cameras: the VAPIX transmit.cgi endpoint is the way to go. A configurable talkback URL override in the ONVIF plugin advanced settings (as suggested in the original issue) would make this cleaner without needing a manual patch.

[bzoel]

Hey @patikoija - care to share the edits you made to use transmit.cgi?