PSA: More standardized getStats() metrics in M76

[Henrik Boström]

For quite some time, several important metrics have only been available in the non-standard getStats() API (goog-stats), preventing applications from migrating to the promise-based getStats() API that shipped over two years ago.

In M76, the key metrics identified in Issue 10428: Unblock Migration to new getStats() API have been implemented (see issue for more details).

The new M76 stats are:

- insertedSamplesForDeceleration, removedSamplesForAcceleration (makes googExpandRate and googAccelerateRate obsolete)

- silentConcealedSamples (makes googPreemptiveExpandRate obsolete)

- fecPacketsReceived, fecPacketsDiscarded (makes googSecondaryDecodedRate and googSecondaryDiscardedRate obsolete)

- roundTripTime and other RTCRemoteInboundRtpStreamStats metrics (makes googRtt obsolete)

- totalEncodedBytesTarget (makes googTargetEncBitrate obsolete)

- jitterBufferDelay and jitterBufferEmittedCount for video (audio-equivalent already exists; together makes googJitterBufferMs obsolete)

- qualityLimitationReason (makes googBandwidthLimitedResolution, googCpuLimitedResolution obsolete)

- RTCMediaSourceStats including width, height and framesPerSecond before encoding (makes googFrameWidthInput, googFrameHeightInput and googFrameRateInput obsolete; and goog*[Sent/Received] are already obsolete)

- totalPacketSendDelay (makes googBucketDelay obsolete)

In previous milestone, M75:

- retransmittedBytesSent, retransmittedPacketsSent (makes googActualEncBitrate obsolete by subtracting from bytesSent)

- totalEncodeTime (makes googAvgEncodeMs obsolete and googEncodeUsagePercent unnecessary)

- lastPacketReceivedTimestamp (together with framesDecoded/framesReceived allows detecting freezes, similar to googInterframeDelayMax but not as good for smaller glitches)

- contentType (makes googContentType obsolete)

A follow-up PSA will contain a guide to aid developers in migrating to the standard API; the old and new metrics don't map 1:1.

[Henrik Boström]

See also,

Spec: https://w3c.github.io/webrtc-stats/

Implementation Status: https://cs.chromium.org/chromium/src/third_party/webrtc/api/stats/rtcstats_objects.h

[Henrik Boström]

See the Chrome Standard getStats() Migration Guide for mappings between the legacy and standard metrics.

[Xiaosha Xing]

Where do we find `insertedSamplesForDeceleration`? Is it supposed to be in audio receiver track from M76?

On Wednesday, June 12, 2019 at 2:05:24 PM UTC+2, Henrik Boström wrote:

[MFC Alerts]

ssrc.googNacksReceived

Only applicable to outbound video ssrcs.

inbound-rtp.nackCount

Shouldn't this be outbound-rtp.nackCount?

From https://w3c.github.io/webrtc-stats:

inbound-rtp.nackCount - Count the total number of Negative ACKnowledgement (NACK) packets sent by this receiver.

whereas

outbound-rtp.nackCount - Count the total number of Negative ACKnowledgement (NACK) packets received by this sender.

[Dennis]

using the test page https://webrtc.github.io/samples/src/content/peerconnection/constraints/ , I do not see 'fecPacketsReceived' in any report.