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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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trackframeskeyframesnackplifirvideo

Frame and packet counters (feature)

Track-level cumulative counters (frames, key frames, QP sum, and NACK/PLI/FIR feedback) summarising a track's lifetime volume and loss recovery.

Description

Track-level features, extracted per media track into features_track, read from the last getStats.

Cumulative counters describing a track's lifetime:

Extracted by the open-source rtcstats-features package.

Why it matters

These counters are the raw material for loss and quality ratios. nackCount, pliCount, and firCount are recovery signals: they rise when packets are lost and the receiver has to ask for retransmissions or fresh key frames, so a high count per minute of video is a direct symptom of a lossy path. keyFrameCount relative to frameCount shows how often the stream had to reset (frequent key frames waste bitrate). qpSum divided by frameCount approximates average quantization, a rough encoded-quality proxy.

Common values

  • Interpret as rates (per second or per frame), not absolutes: a long call naturally accumulates large counts.
  • Elevated pliCount/firCount per minute indicates repeated key-frame requests, usually from packet loss.

SQL example

Average NACK/PLI/FIR per inbound video track, on connections that actually established:

SELECT
  AVG(track.nack_count) AS avg_nack,
  AVG(track.pli_count)  AS avg_pli,
  AVG(track.fir_count)  AS avg_fir
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 = 'inbound';  -- 'inbound' or 'outbound'

Related features

  • Freezes - the user-visible consequence when recovery fails.
  • Quality limitation - encoder-side constraints on outbound video.
  • Codec - which codec produced these frames.

See also