mediamtx: substitute hostname/IP before start#977
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The shipped mediamtx.yaml uses placeholder values (raspberrypi, 192.0.2.1) for webrtcAdditionalHosts that lib/mediamtx.js is supposed to replace at runtime. Previously the substitution only ran on the backend's wired_controller observable, so any reset or redeploy of /etc/mediamtx.yaml left the placeholders advertised in WebRTC ICE candidates. Browsers cannot resolve "raspberrypi", silently fail peer-connection negotiation, and the dashboard preview spins forever with no visible error. Run lib/mediamtx.js as ExecStartPre so every mediamtx start unconditionally substitutes the real values into the file before mediamtx loads it. Also order the unit after network-online.target so the IP detection in getWiredAddress() is valid when the script runs. Verified on Node 24.15 (the version that ships): the IIFE at the bottom of lib/mediamtx.js gates on import.meta.main, which Node now supports natively, so no source change to lib/mediamtx.js is needed.
Run lib/mediamtx.js from the cam path's runOnInit hook in mediamtx.yaml rather than a systemd ExecStartPre, so the hostname/IP substitution also runs when mediamtx is started outside systemd (e.g. `just dev`). mediamtx watches the config file and hot-reloads after the rewrite; runOnInit fires once because lib/mediamtx.js only edits the global webrtcAdditionalHosts, leaving the cam path config unchanged. Keep network-online.target so the wired IP is available when it runs.
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ammended-mediamtx: use runOnInit instead of ExecStartPre for yaml substitution |
sonnyp
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Summary
An error I found in testing this week. This is to fix the silent WebRTC failure that causes the dashboard preview iframe to spin forever after any reset or redeploy of
`/etc/mediamtx.yaml`.
Root cause
`os/mediamtx/mediamtx.yaml` ships with placeholders in `webrtcAdditionalHosts`:
```yaml
webrtcAdditionalHosts: [
192.0.2.1, # placeholder IP
raspberrypi, # placeholder hostname
raspberrypi.local, # placeholder hostname.local
...
]
```
These are runtime-substituted by `lib/mediamtx.js`, called from the backend's `network.js` whenever its
`wired_controller` observable emits. If the substitution hasn't happened (boot race, image redeploy, manual revert,
config reset), MediaMTX advertises `raspberrypi` in WebRTC ICE candidates. Browsers try to resolve it, get `no such
host`, and silently fail peer-connection negotiation — the dashboard preview just shows an infinite spinner with no
visible error.
The failure surfaces in mediamtx logs as:
```
INF [WebRTC] [session ...] closed: lookup raspberrypi on :53: no such host
```
…but HTTP-level probes (curl on `/cam/`, `/cam/index.m3u8`) all return normal content, so the bug is invisible to
anything but a real browser doing WebRTC ICE.
Fix
Run `lib/mediamtx.js` as `ExecStartPre` so the YAML is always rewritten with the device's real hostname/IP before
MediaMTX loads it. Also bump the unit's network dependency from `network.target` to `network-online.target` so
`getWiredAddress()` can read the IP when the script runs.
No change needed to `lib/mediamtx.js` — its trailing IIFE already gates on `import.meta.main`, which Node 24 (the
version we ship) supports natively. Invoking the file directly runs the substitution and exits.