The audio capture loop runs at ~50Hz publishing every buffer's peak via overwrite; the UI stats poll reads at 1Hz. With overwrite semantics the UI sees one of every ~50 audio frames per second — loud transients between reads were invisible to the VU meter.
New design: NdiReceiver maintains an atomic high-water mark, max-updated on each audio frame via CompareExchange CAS loop. IsoPipeline.GetStats now calls ConsumeAudioPeak() which atomically reads + resets to 0, so the next UI tick reflects the loudest sample seen in the next 1s window.
Added PeekAudioPeak() for non-consuming reads (e.g. external diagnostics dashboards that poll faster than the UI).
FakeNdiInterop gained a ReceiverAudioPeaks queue + CaptureAudioPeak override so tests can drive the audio path. 4 new tests in NdiReceiverTests cover: empty case, single-frame consume+reset, max-hold across 3 frames, no-frame leaves high-water mark untouched. 104 + 46 + 9 = 159/159 passing.
Adds an NdiGroupSettings record carrying optional comma-separated NDI group lists for the finder and the senders. Extends INdiInterop.CreateFinder / CreateSender with optional groups arguments and populates NDIlib_find_create_t.p_groups and NDIlib_send_create_t.p_groups via P/Invoke. IsoController reads the settings on construction, threads DiscoveryGroups into NdiDiscoveryService and OutputGroups into IsoPipelineConfig, and exposes SetGroupSettingsAsync for runtime updates (group changes apply on next process restart so live pipelines aren't orphaned).
This unblocks the 'transcoder' topology where Teams broadcasts NDI on a private group (e.g. teamsiso-input) and TeamsISO re-emits clean normalized streams on Public — keeping raw, wrong-framerate Teams sources off the production network.
EngineConfig schema is JSON-back-compat: existing config.json files (no NdiGroups field) deserialize with NdiGroups=null and load as NdiGroupSettings.Default. UI surface for these settings comes in a follow-up.
Tests: 72/72 passing (was 69) — added IsoController coverage that group settings are read from ConfigStore on startup, passed to the finder, threaded into per-pipeline config, and round-trip through SetGroupSettingsAsync/Save/Load.
