Metrics help you explain what a client is sending, receiving, and playing. Start with the overview measurements, then follow the affected track or stream when something looks wrong. A missing measurement means the browser or current interval did not supply enough evidence; it does not mean the value is zero.

When interpreting a value, distinguish its origin: browser stat, adapted/inferred stat, derived measurement, declared context, detector/score result, identity/lifecycle metadata. Application-defined measurements belong to application extensions.

Monitor ownership#

The authoritative raw-stat families and exact field sets are in the schema inventory. Their monitor ownership is:

The full field inventory is intentionally not reduced to the above examples.

Core formulas#

Let Δx = positiveDelta(current, previous), dtMs = current.timestamp − previous.timestamp, dt = dtMs/1000. positiveDelta returns undefined, not zero, on missing inputs or a backwards counter. Each consumer may handle that differently; some explicitly coalesce to zero. Read the formula appendix for every assignment and its guards.

Aggregates and transport stability#

PC sums distinguish audio/video/data-channel directions. Quality-loss averages include streams that actually carried relevant packets; missing measurement differs from zero loss. RTT paths are kept separate (rtcpRttInSec, iceRttInSec), with current RTT preferring RTCP and falling back to ICE. Root avgRttInSec averages PC values and returns -1 with no PCs. PC legacy loss sums and newer per-stream means are not interchangeable.

transportStability is the normalized MOS-like value produced by utils/transportStability.ts: effective latency is RTT/2 + 2×jitter +10 ms; a piecewise latency impairment and 2.5×loss-percent reduce R; a cubic maps clamped R to MOS; normalized against this model’s best/worst MOS. It requires all three measurements. It is not a direct measurement of user satisfaction or a selected-pair-switch counter. client-monitor-js/src/utils/transportStability.ts.

Missing values and resets#

There is no single universal nullification pass. The current code uses several distinct mechanisms:

• Missing raw inputs: InboundRtpMonitor explicitly replaces known fields, including undefined; several other monitors use Object.assign and can retain omitted properties. Derived assignments are conditional, so some previous derived values can remain. Do not promise universal freshness without checking the owner.
• Backwards counters: positiveDelta returns undefined; MediaPlayoutMonitor explicitly converts some such deltas to zero. Remote RTCP repeated/stale timestamps clear interval readings. Inbound repeated timestamps replace raw fields but return before recomputing derived values; outbound returns earlier.
• Shared windows: SlicedWindow uses null for unavailable totals, rejects repeated timestamps, resets across excessive gaps and requires full slices. N samples span N−1 intervals. Detection/recovery are different slices; inspect their configured offsets rather than assuming a trailing duration in milliseconds.
• Paused/ended/background/muted tracks: individual detectors stand down according to their own guards. There is no blanket rule that every detector handles every gate identically. Missing-input branches can preserve an open issue while publishing inputsUnavailable, whereas some detectors resolve it.
• Zero score: full-scale deductions clamp the affected component to zero. Connectivity issues are deliberately not charged again on the PC; dry-track issues can zero media components. There is no global “any network fault nullifies every score” rule.
• Aggregate absent dimensions: undefined/null dimensions are omitted from client RMSE; no measurable dimensions causes calculator early return, leaving the root’s previous/default score, which starts at 5. This differs from documentation saying the root necessarily becomes undefined.
• Wire absence: undefined properties disappear under JSON serialization; Avro nullable fields and generated TS optional fields are separate representations. On-change ICE omissions must be retained by the receiver, but current observer code does not retain them (known limitations).

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