Direct answer
Inspect the audio track before changing volume controls. AAC and G.711 are different codecs and payload formats; select a camera profile the viewer supports, then verify that the microphone is enabled and permitted for the account.
Why this happens
A camera can send valid video with an audio codec the client does not decode. Some models also disable audio per stream, omit it from substreams or restrict it by regional setting.
Inspect the advertised tracks and codec parameters before assuming a viewer or network problem.
A controlled test
Probe the exact main and substream URLs, note codec and sample rate, and test playback with one trusted diagnostic client.
Change one variable at a time. Keep the camera model, firmware, endpoint and account recorded; then test network reachability, protocol response, media transport and decoding as separate layers.
Use a dedicated view-only account and a trusted local diagnostic tool. Redact credentials, private addresses and identifying data before sharing output.
Diagnostic sequence
| Check | Action | Evidence of progress |
|---|---|---|
| Track | Confirm an audio media section is advertised. | The stream contains an audio track. |
| Codec | Identify AAC, PCMU, PCMA or another format. | The viewer supports the exact payload. |
| Camera | Enable the microphone and audio for that profile. | Packets arrive on the audio track. |
| Permissions | Verify the view-only account can access audio. | Playback succeeds without administrator rights. |
Evidence to keep
Record codec, sample rate, channel count and which profile contains audio. That evidence is more precise than “microphone does not work.”
Boundary and safety note
Listening and two-way talk are separate features; a playable inbound audio track does not prove talkback support.
For remote viewing, use a managed VPN instead of exposing RTSP or camera administration ports directly to the public internet.
SmartRTSP
SmartRTSP is a camera-focused RTSP and ONVIF viewer for Apple devices, Windows and Android. It fits direct viewing, discovery and multi-camera checks; keep a dedicated NVR or VMS when continuous recording, evidence export or centralized enterprise controls are required.
Frequently asked questions
What are PCMU and PCMA?
They are G.711 variants commonly used by IP cameras, with different companding laws.
Why does the main stream have audio but the substream does not?
Audio can be enabled per profile or omitted by the camera implementation.
Does ONVIF discovery guarantee audio?
No. Profile and optional-feature support must be verified for the exact device and client.
Primary references
- IETF RFC 7826 — Real-Time Streaming Protocol 2.0
- ONVIF — Profile T for advanced video streaming
- FFmpeg — RTSP protocol options and examples
Related SmartRTSP guide
Open related guideCompare common camera audio codecs and diagnose silent playback without confusing microphone settings with decoder support.