Reading RTCStatsReport for AI Voice Agents: 2026 Field Guide

Server logs lie about audio quality. The only ground truth is what the receiver's jitter buffer experienced — and that is exclusively in `RTCStatsReport`. For AI voice in 2026, getStats is the SLO data plane.

Why getStats matters more for AI voice

Old-school voice apps measured MOS at the SBC. AI voice agents do not have an SBC at the user edge — the browser is the edge. A 2% packet-loss spike in the user's coffee-shop Wi-Fi never appears in your server traces. It only appears in `getStats` on the browser, and only the values that come from the receiver-side report tell you what actually played.

The W3C Statistics API (webrtc-stats) defines stable identifiers for every relevant metric: `inbound-rtp`, `outbound-rtp`, `remote-inbound-rtp`, `candidate-pair`, `media-source`, and `media-playout` (the new one, important for jitter-buffer health). The 2026 update added `ecn-ce-marks-received` for L4S detection and finalized `audioLevel` semantics across browsers.

Architecture pattern

```mermaid flowchart LR Browser -- getStats every 2s --> Collector Collector -- diff over time --> Metrics[(Prometheus / Datadog)] Metrics --> SLO[Voice SLO dashboard] Metrics --> Alert[PagerDuty if p99 jitter > 30ms] ```

You poll `pc.getStats()` once every 2 seconds, diff the cumulative counters against the previous sample, and emit gauge metrics. Sub-second polling does not help — the underlying counters update at most once per RTCP report (every 1–5 s).

Key fields to track

• inbound-rtp: `packetsLost`, `jitter`, `packetsReceived`, `bytesReceived`, `audioLevel`.
• media-playout: `totalSamplesReceived`, `concealedSamples`, `silentConcealedSamples`. Concealed samples are the smoking gun for "did the user hear glitches?"
• remote-inbound-rtp: `roundTripTime`, `fractionLost`. Tells you what the agent sees coming from the user.
• candidate-pair (selected): `currentRoundTripTime`, `bytesSent`, `bytesReceived`, `localCandidateId` / `remoteCandidateId` (use to detect TURN relay).
• media-source: `audioLevel`, `totalAudioEnergy`. Use sparingly — they leak speaker activity.

CallSphere implementation

CallSphere ships getStats collection in the browser SDK that powers all six verticals (real estate, healthcare, behavioral health, legal, salon, insurance). Polling at 2 s, we ship 14 fields per call to a Prometheus pushgateway routed through our Pion Go gateway 1.23 over NATS to the 6-container pod (CRM, MLS, calendar, SMS, audit, transcript).

The single most useful derived metric is `concealedSamples / totalSamplesReceived` — anything above 1.5% means the AI agent's response was audibly degraded, regardless of how clean the model output was. Across 37 agents, 90+ tools, 115+ database tables we alert on p99 RTT, p99 jitter, and concealment ratio. Real Estate (OneRoof, /industries/real-estate) sees the lowest concealment because of the noise-suppression worker described in the Insertable Streams post. SOC 2 + HIPAA logs only carry derived numbers — never raw audio level. Pricing $149/$499/$1499; affiliates 22% — see /affiliate.

Code snippet

```ts let prev = new Map(); setInterval(async () => { const stats = await pc.getStats(); for (const [id, report] of stats) { if (report.type === "inbound-rtp" && report.kind === "audio") { const last = prev.get(id); if (last) { const dPackets = report.packetsReceived - last.packetsReceived; const dLost = report.packetsLost - last.packetsLost; const lossRate = dLost / Math.max(1, dPackets + dLost); emit("voice.inbound.lossRate", lossRate); emit("voice.inbound.jitter", report.jitter); } prev.set(id, report); } if (report.type === "media-playout") { emit("voice.playout.concealed", report.concealedSamples / Math.max(1, report.totalSamplesReceived)); } if (report.type === "candidate-pair" && report.selected) { emit("voice.rtt", report.currentRoundTripTime); emit("voice.relay", report.remoteCandidateId.includes("relay") ? 1 : 0); } } }, 2000); ```

Build steps

1. Poll every 2 s; diff cumulative counters; never store absolute values.
2. Tag every metric with `agentId`, `vertical`, `sessionId`, `browser`.
3. Route raw values through a server you control before any third-party APM. Browser-emitted PHI in stats is a real concern.
4. Build SLO dashboards on three numbers: RTT, jitter, concealment ratio.
5. Alert on concealment > 1.5% sustained for 30 s. That is the user-noticed bar.
6. Cross-reference `localCandidateId` / `remoteCandidateId` with the candidate-pair report to detect when a session is on TURN.
7. Persist a 24-hour rolling sample for forensic playback; engineers will need it.

Common pitfalls

• Polling `getStats` from the main thread — it is a fast call but during garbage collection it can spike to 30 ms. Schedule on `requestIdleCallback` if you can.
• Treating absolute counters as gauges — `packetsLost` is monotonic. Always diff.
• Ignoring `media-playout` — the smoking gun for user-perceived audio glitches lives only here.
• Cross-tab leakage — multi-tab apps may have multiple PeerConnections. Tag stats per PC.
• Privacy via `audioLevel` — do not ship raw `audioLevel` to a third-party APM; it leaks speaker activity timing.

FAQ

Is concealedSamples in every browser? Yes — `media-playout` is in Chrome 110+, Safari 17+, Firefox 122+.

Why not poll faster? RTCP only updates the underlying counters every 1–5 seconds; polling faster gives no new data.

What about MOS? No browser computes MOS for you. Compute it server-side from packet loss, jitter, and RTT using ITU-T G.107.

Are stats privacy-sensitive? `audioLevel` can leak whether someone is speaking. Strip it from anything that hits a third-party APM.

Is there a single field that summarizes call quality? No — combine RTT, jitter, and concealment. A weighted score works well.

What is the cost of `getStats`? Sub-millisecond on modern hardware; safe to call every 2 s.

Does it work in workers? No — `getStats` is on the main thread or the document only. Pull the data out, then ship to a worker for analysis.

Can I correlate stats with model latency? Yes — emit `response.first_audio_delay` from the DataChannel side and join with `getStats` server-side.

Production playbook for AI voice teams in 2026

Three rules from shipping getStats observability across 37 agents:

1. Compute MOS server-side. ITU-T G.107 plus packet loss, jitter, and RTT gives you a reliable per-call MOS proxy. Do not trust client-side approximations.
2. Tag the candidate type. `relay` vs `srflx` vs `host` is the single best predictor of call quality. Tag every metric with it.
3. Sample, do not aggregate, on the client. Send raw per-second samples; aggregate in your TSDB. Aggregation on the client throws away the noise pattern that points at the actual problem.

The most underrated metric is `media-source.totalAudioEnergy` divided by elapsed time — silent calls have a known energy-vs-time signature, and "user said nothing for 30 s" is a very specific failure mode that needs a dedicated alert.

Watch list 2026

• `ecn-ce-marks-received` lands in Chromium 132 and lights up L4S adoption tracking — see the L4S post.
• `media-playout.delay` is being added to the spec; it gives you the actual playout delay, not just concealment.
• `remote-outbound-rtp` becomes mandatory in the 2026-Q3 spec update; previously many browsers omitted it, breaking RTT calculations in some flows.
• Privacy guidance is being formalised in webrtc-stats — expect tighter rules on what `audioLevel` and `totalAudioEnergy` you can ship to third parties without consent.

Sources

• https://www.w3.org/TR/webrtc-stats/
• https://bloggeek.me/getstats/
• https://www.100ms.live/blog/measuring-webrtc-call-quality-part-1
• https://www.webrtc-developers.com/interpreting-webrtc-statistics-with-rtcstats/
• https://github.com/peermetrics/webrtc-stats
• https://github.com/oanguenot/webrtcmetrics

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