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WebRTC Metrics

A comprehensive overview of WebRTC statistics, derived calculations, extracted features, and observable signals, to better understand call quality, connectivity, and user experience in rtcStats

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trackvideooutboundcpubandwidthquality

Quality limitation (feature)

Track-level features breaking down why outbound video was degraded (CPU, bandwidth, or other) as a fraction of the track's lifetime, plus resolution-change count.

Description

Track-level features, extracted per outbound video track into features_track, from last-getStats ratios.

These features decompose why the encoder had to reduce quality, as a fraction of the track's lifetime:

  • cpuQualityLimitationPercentage - fraction of time the encoder was CPU-limited.
  • bandwidthQualityLimitationPercentage - fraction of time it was bandwidth-limited.
  • otherQualityLimitationPercentage - fraction limited by other.
  • qualityLimitationResolutionChanges - cumulative count of resolution changes triggered by quality limits.

Extracted by the open-source rtcstats-features package.

Why it matters

When outbound video looks bad, the first question is always whose fault is it: the machine or the network? These features answer it directly. A high cpuQualityLimitationPercentage means the encoder couldn't keep up (an underpowered device, or too many concurrent streams); a high bandwidthQualityLimitationPercentage means the network couldn't carry the target bitrate. The two demand opposite responses (lower resolution/framerate vs. improve the path), so splitting them at the population level tells you where to invest. qualityLimitationResolutionChanges counts how often the encoder had to renegotiate resolution, a marker of unstable conditions.

Typical values

  • Good: all limitation percentages near 0.
  • Concerning: a sustained CPU or bandwidth fraction above ~0.2 across a cohort.
  • Many qualityLimitationResolutionChanges indicates volatile CPU or network conditions.

SQL example

Average limitation breakdown for outbound video, on connections that actually established:

SELECT
  AVG(track.cpu_quality_limitation_percentage)       AS avg_cpu_limited,
  AVG(track.bandwidth_quality_limitation_percentage) AS avg_bw_limited,
  AVG(track.other_quality_limitation_percentage)     AS avg_other_limited
FROM features_track AS track
JOIN features_connection AS connection ON connection.id = track.connection_id
WHERE connection.connected           -- only connections that reached 'connected'
  AND track.kind = 'video'           -- 'audio' or 'video'
  AND track.direction = 'outbound';  -- 'inbound' or 'outbound'

Related features

See also