NMOS

bilbycast-edge implements the broadcast-audio subset of the AMWA NMOS specifications:

Spec	Endpoint	Coverage
IS-04 v1.3	/x-nmos/node/v1.3/	self, devices, sources, flows, senders, receivers
IS-05 v1.1	/x-nmos/connection/v1.1/	single sender/receiver staged + active + transporttype + constraints
IS-08 v1.0	/x-nmos/channelmapping/v1.0/	io, map/active, map/staged, map/activate (active map persists to disk)
BCP-004	embedded in IS-04 receiver caps	constraint_sets for ST 2110 audio inputs
mDNS-SD	_nmos-node._tcp	best-effort registration via the mdns-sd crate

Format detection

Each flow’s input is classified at IS-04 list time:

• InputConfig::St2110_30 / St2110_31 → urn:x-nmos:format:audio
• InputConfig::St2110_40 → urn:x-nmos:format:data
• everything else → urn:x-nmos:format:mux

The same classifier drives the receiver caps block. Audio receivers advertise BCP-004 constraint sets keyed by urn:x-nmos:cap:format:* URNs (sample_rate, channel_count, sample_depth) so NMOS controllers can reject incompatible senders before activation.

BCP-004 receiver capabilities

{
  "caps": {
    "media_types": ["audio/L16", "audio/L24"],
    "constraint_sets": [{
      "urn:x-nmos:cap:format:media_type": { "enum": ["audio/L16", "audio/L24"] },
      "urn:x-nmos:cap:format:sample_rate": { "enum": [{ "numerator": 48000 }] },
      "urn:x-nmos:cap:format:channel_count": { "enum": [2] },
      "urn:x-nmos:cap:format:sample_depth": { "enum": [24] }
    }]
  }
}

ST 2110-40 receivers advertise media_types: ["video/smpte291"]. Non-ST-2110 receivers continue to advertise the historical video/MP2T shape so existing NMOS controllers don’t break.

PTP clocks

When any flow on the node sets clock_domain, the IS-04 /self resource includes a single PTP clock entry (name: "clk0", ref_type: "ptp"). Sources whose flow has clock_domain set reference this clock by name. The locked field is reported as false until live PTP integration lands; the manager UI uses FlowStats.ptp_state.lock_state for the real view — see ST 2110 for the PTP architecture.

IS-08 audio channel mapping

The IS-08 endpoints expose every ST 2110-30/-31 audio input and output under /io. The active map is persisted to <config_dir>/nmos_channel_map.json (next to config.json) and reloaded on startup. Both staged and active maps support the standard PUT/POST + activate workflow.

Bilbycast does not currently re-route channels internally — the map is a passthrough — but the endpoints exist so external NMOS controllers can stage and activate maps and the manager UI can render the channel layout.

Bounds: at most 1024 outputs per map, at most 64 channels per output. Controllers exceeding these limits receive a 413 PAYLOAD_TOO_LARGE response.

mDNS-SD registration

On startup the edge calls a small mdns-sd helper to register _nmos-node._tcp on the local link. Failures (no multicast on the selected interface, daemon errors) are logged once and swallowed; flow startup is never blocked. The handle is dropped on process exit, which unregisters the service cleanly.

Backward compatibility

Multi-essence audio + data resources are additive — old NMOS controllers that only consumed format:mux continue to work because mux flows are still classified the same way. The IS-08 router is mounted under a fresh URL prefix and is invisible to controllers that don’t speak it. The mDNS-SD registration is supplementary to manual NMOS registry configuration.

Pending external validation

The following items are deferred until matching tooling becomes available in the test lab:

• AMWA NMOS Testing Tool runs against IS-04, IS-05, IS-08, BCP-004. Expected pass matrix:
  • IS-04: pass on test_01 (resources have valid UUIDs / formats / transports) through test_19 (clocks).
  • IS-05: pass on staged/active round-trip for sender + receiver, with transport-file SDP advertisement for ST 2110 senders.
  • IS-08: pass on io, map/active, map/staged, map/activate happy paths.
  • BCP-004: pass on receiver caps containing media_types plus a constraint_sets block matching the configured sample rate / channel count / bit depth.
• Sony NMOS Commissioning Tool end-to-end smoke against a real Lawo or Riedel device.