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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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trackcodecvideoaudiosdp

Codec (feature)

Last updated Applies tortcstats-serverrtcstats.com

Track-level features recording the negotiated codec MIME type and its SDP fmtp parameters for each media track.

Description

Track-level features, extracted per media track into features_track.

These features record which codec a track actually used, read from the first getStats:

  • codecMimeType - the MIME type of the negotiated codec (e.g. video/VP8, video/H264, audio/opus).
  • codecSdpFmtpLine - the SDP fmtp parameters for that codec ('' if none).

Extracted by the open-source rtcstats-features package.

Why it matters

codecMimeType tells you what your endpoints negotiated, which is not always what you offered. After a codec rollout (say, enabling AV1 or VP9), this is how you confirm real-world adoption across browsers and versions. Codec distribution also explains quality and CPU differences between cohorts, and codecSdpFmtpLine exposes profile-level detail (H.264 profile-level-id, Opus FEC/DTX flags) that can differ subtly between clients and cause interop surprises.

Common values

  • Video: video/VP8, video/VP9, video/H264, video/AV1.
  • Audio: audio/opus, audio/PCMU, audio/PCMA.
  • codecSdpFmtpLine: codec-specific parameter string, or empty.

SQL example

Codec distribution across all outbound tracks on connections that actually established:

SELECT
  track.codec_mime_type,
  COUNT(*) AS tracks
FROM features_track AS track
JOIN features_connection AS connection ON connection.id = track.connection_id
WHERE track.codec_mime_type IS NOT NULL
  AND connection.connected          -- only connections that reached 'connected'
  AND track.direction = 'outbound'  -- 'inbound' or 'outbound'
  AND track.kind = 'video'          -- 'audio' or 'video'
GROUP BY track.codec_mime_type
ORDER BY tracks DESC;

See also