*Contact emails* h...@chromium.org, h...@chromium.org *Background* I attempted to remove this feature before but had forgotten to file an intent to deprecate, background here <https://groups.google.com/a/chromium.org/g/blink-dev/c/RsIktnGhHqw/>.
*Specification* The getStats() API spec is here <https://w3c.github.io/webrtc-stats/> and it contains all the metrics. The deprecated metrics are also listed, but in the obsolete section <https://w3c.github.io/webrtc-stats/#obsolete-rtcmediastreamtrackstats-members>. There's an open issue to remove obsolete metrics from the spec as soon as they are unshipped from modern browsers. This is considered a blocker for the document to reach Proposed Recommendation status. *Summary* WebRTC is a set of JavaScript APIs (spec <https://w3c.github.io/webrtc-pc/>) that allow real-time communication between browsers. For the relevant metrics being removed, we're only talking about the WebRTC use case that is sending or receiving audio or video (typically Video Conferencing use cases), not the data channel use cases that is a popular WebRTC use case, since data channel only use cases would never have any tracks/streams. RTCPeerConnection.getStats() returns a map of string-to-objects, where each object is one of the dictionaries defined in the stats spec. The reason an app calls getStats() is mostly to report quality metrics (send and receive resolutions, bitrates, glitches, video QP, etc) which can be important for A/B experimentation. It can also be used in a way that impacts app logic or even UX inside the app. Most common use case I can think of: poll getStats() at 10 Hz and render volume bars for each participant based on volume levels from stats objects. The deprecation in question is to remove some stats objects that were made obsolete several years ago: all metrics on the "track" dictionary have been moved to non-obsolete objects ("inbound-rtp", "outbound-rtp", "media-source"). Reasons for wanting to deprecate include: - Spec-compliance: needed for browser implementations to align and for the spec to become Proposed Recommendation. - Web compat: Firefox never implement "track" or "steam" <https://wpt.fyi/results/webrtc-stats/supported-stats.https.html?label=experimental&label=master&aligned> due to them being obsolete. - Performance: the duplicated metrics make up ~40% of the stats report size, which can be a significant number of bytes in larger meetings and it is common for apps to poll getStats() 10 times per second. - Tech debt: unblock removal of 1400 LOC. In the meantime, the obsolete metrics is duplicated in several places of the stats report. *Risks* *- Impossible to properly measure usage* Because stats objects are exposed as JavaScript dictionaries, and because apps have to iterate all objects of the stats report in order to find the ones they are interested in or if they just dump all the data without filtering, there is no way to measure how big the dependency is on track in the real world. While we lack use counters, we have some positive signs: - Because Firefox does not have "track" or "stream" stats, any app that can run on Firefox already exercises the paths of these not existing. - An experiment to "unship deprecated metrics" has been running at 50% Canary since October <https://groups.google.com/a/chromium.org/g/blink-dev/c/RsIktnGhHqw/m/3iqjODsMBwAJ>, giving developers testing Canary a heads-up. Nobody complained until the experiment reached Stable. - We got to 50% Stable in M109 and while we're in the process of rolling it back now due to breaking twilio-video.js <https://github.com/twilio/twilio-video.js/issues/1968>, it's interesting to note that this is the only breakage we are aware of (that does not mean there aren't more breakages, but I believe this at least says something about the severity). *- Selenium et al typically starts browsers from fresh profiles and hence does not know the finch trial seed* The most likely explanation for breakage is not testing Canary or test environments not having access to Finch experiments. This makes the behavior on Stable a surprise. *- To have a Reverse Origin Trial or not to have a Reverse Origin Trial?* Migrating should require so few lines of code (look for stats.type == 'inbound-rtp' instead of stats.type == 'track', for example) that it seems to be a bigger hurdle for a developer to enroll in the trial than to simply fix their code. *- Compatiblity risk* There is one particular metric out of all metrics that, if you run Safari, does not exist on "inbound-rtp" yet. This can be a problem, but again is probably not a big problem because this particular metric was never implemented on Firefox so apps already need to survive without it, and it is very easy to write a fallback path for the Safari case: let trackIdentifer = null; // In Firefox this will never be set regardless. if (inboundRtp.trackIdentifier) { // Spec-compliant browser. trackIdentifier = inboundRtp.trackIdentifier; } else if (inboundRtp.trackId) { // Fallback-path for Safari or 1+ year old Chromium browsers. trackIdentifier = report.get(inboundRtp.trackId).trackIdentifier; } *Proposal* Rollback to 0% Stable but keep the "unship deprecated" experiment at 50% Canary/Beta. Wait for Twilio to fix their issue and do another rollout attempt. Keep a slower rollout pace next time. I see limited amount of value in a Reverse Origin Trial since it appears to be more effort to register to the trial than to fix the issue, if you are affected. I do prefer to have the feature enabled-by-default in M111+ and overwrite that default via Finch rather than the other way around as to not "turn off the fire alarm" for non-Finch testing environments. I realize that is not perfect (what if you run in a non-Finch environment) but it would reduce overall risk. -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscr...@chromium.org. To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/5ecf1ea6-c16c-464a-b529-439e05e4feedn%40chromium.org.
