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feat(video): force a keyframe when a joiner wants a fresh group - #6048
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
moq-video capture and the js/publish WebCodecs encoder advertise track::Info::refresh (ratio 2) and cut a keyframe on the next frame whenever Demand::wanted passes the largest group. The configured GOP stays the upper bound. Capture advertises only when every backend the encoder may open honors a cut, so V4L2 never advertises. The 500ms floor between forced keyframes is gone from Cuts and the WebCodecs encoder: the ratio already rate-limits joins by bytes. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Quest outcome: everything is implemented, and the PR stays a draft until the maintainer settles the ratio's home and default. Implemented recommendations: a fixed ratio of 2 with no public field, every
(Written by Claude Opus 5.5) |
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WalkthroughJavaScript and Rust video publishers now advertise refresh information and can force keyframes when subscriber demand exceeds the group already served. Rust capture advertises refresh only when all matching encoder backends support cuts. Cut requests no longer use a 500 ms minimum spacing. Documentation and tests were updated, and the video refresh planning document and its required-list entry were removed. Priority: ➖ Normal Merge Risk: 🔵 Low · up to
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| Check name | Status | Explanation |
|---|---|---|
| Title check |  |
The title clearly and concisely describes the main change: forcing a keyframe when a joiner requests a fresh group. |
| Docstring Coverage | |
Docstring coverage is 93.10% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 7 files. (2 skipped: 2 … |
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Check skipped because no linked issues were found for this pull request. |
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| Description check | |
The pull request description directly explains the video refresh implementation, keyframe behavior, refresh advertisement, backend rules, tests, documentation, and quest completion reflected in the ch… |
Full details: Docstring Coverage
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Docstring coverage is 93.10% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 7 files. (2 skipped: 2 unsupported.)
Full details: Description check
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Explanation
The pull request description directly explains the video refresh implementation, keyframe behavior, refresh advertisement, backend rules, tests, documentation, and quest completion reflected in the changeset.
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Inline comments:
Review comments at @doc/lib/js/publish.md:
- Around line 53-54: The documentation around the fresh-keyframe guarantee
should state its relay-cluster limitation: when an upstream subscription already
exists, a new viewer’s refresh request does not reach the encoder and the viewer
may wait for the interval keyframe. Update the prose near keyframeInterval to
qualify the guarantee and describe only the currently shipped behavior.
Review comments at @doc/lib/rs/moq-video.md:
- Around line 30-33: Update the encoder GOP documentation near the discussion of
refresh behavior to state that builds with the v4l2 feature disable refresh for
auto-selected and hardware-selected encoders, including non-V4L2 candidates;
note that explicitly naming a non-V4L2 encoder is excluded, and retain the
driver refusal rationale.
Review comments at @rs/moq-video/src/encode/backend/mod.rs:
- Around line 596-599: Acquire the probe lock with probe::exclusive() before
iterating over NAMED_ONLY, keeping the guard alive for the entire
candidate-opening and can_cut() assertion loop.
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📒 Files selected for processing: 11
doc/lib/js/publish.mddoc/lib/rs/moq-video.mdjs/publish/src/broadcast.tsjs/publish/src/video/encoder.test.tsjs/publish/src/video/encoder.tsquest/m1/refresh/README.mdquest/m1/refresh/video.mdrs/moq-video/src/encode/backend/mod.rsrs/moq-video/src/encode/cuts.rsrs/moq-video/src/encode/encoder.rsrs/moq-video/src/encode/producer.rs
💤 Files with no reviewable changes: 2
- quest/m1/refresh/README.md
- quest/m1/refresh/video.md
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The docs now state that through a moq-lite relay only the join that opens the upstream subscription counts, and that a v4l2 build keeps every Auto or Hardware selection to its GOP. The candidate-promise test holds the probe lock while it opens probe backends, so it cannot pollute another test's log under cargo test. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Merging.
(Written by Claude Opus 5.5) |
Implements the Video quest of the refresh epic: the Rust and browser video publishers advertise
track::Info::refreshand force a keyframe whenDemand::wantedpasses the largest group. It builds only on what is already onmain(track::Info::refresh,Demand::wanted). It does not depend on moq-dev/moq#6030, which carries the demand through relays.The quest left the ratio's home and default for the maintainer to settle. This PR implements the recommended course for each, confirmed by the maintainer below with the alternatives listed.
Summary
Control::new/publish_capture): the track advertisesrefresh: Some(2)when every backend the configuredCodec+Kindmay open honors a cut. A new staticcutsflag on each backend candidate answers that before the track exists. V4L2 says no (a driver reports its force-keyframe control only at open), soKind::Autoon a build with thev4l2feature never advertises. Each frame, the capture loop cuts whenDemand::wantedpasses the track's largest group. A no-cut backend never does.Cutsis simpler: no 500 ms floor, no timestamps, no keyframe bookkeeping. It coalescesControl::cutrequests by their running count and joins by the wanted group (which only grows), and the opening keyframe of a fresh encoder still serves everything asked before it.Broadcast.video()rendition track advertisesrefresh: 2. The WebCodecs encoder setskeyFrame: trueon the next frame whendemand().wantedpasses what its last keyframe answered. The 500 msMIN_CUT_INTERVALis gone.Config::gop,keyframeInterval) is still the upper bound between keyframes.doc/lib/rs/moq-video.mdanddoc/lib/js/publish.md(including that through a moq-lite relay only the join opening the upstream subscription counts until moq-dev/moq#6030, and that av4l2build never refreshes anAuto/Hardwareselection), plus the rustdoc/TSDoc forControl::cut,Encoder::cut,Encoder.cut()andkeyframeInterval.Required.Measurement behind the ratio
Encoded with x264
veryfast/zerolatency, CBR, a 2 s GOP and no scene cuts: Big Buck Bunny 720p24 at 2.5 Mbps, a 1080p30 street clip at 4 Mbps, and a 720p30 security camera at 2 Mbps. The simulation used the real frame sizes, with Poisson joins and a forced keyframe costing the average I-frame. Each cell is the mean bytes a joiner downloads before it can decode, then the extra bitrate everyone pays:A 2 s realtime GOP holds about 3 to 5 keyframes of deltas, so R ≥ 4 barely triggers. R = 2 roughly halves what a joiner downloads, and costs about 1% at one join every ten seconds and 10 to 13% at one join a second. The join rate is per hop: each relay judges a join against its own cache.
Public API and wire impact
encode::Control::cutno longer spaces keyframes 500 ms apart. Capture tracks now carryrefresh: Some(2).Encoder.cut()no longer spaces keyframes.Broadcast.video()tracks advertise refresh, and its docs now say the producer must answerdemand().wanted.rs/moq-video/MIGRATE.mdandjs/publish/MIGRATE.mdcover the removed spacing (debounce your own calls) and the refresh contract.Decisions (confirmed)
The maintainer confirmed each decision below, taking the recommended course; the alternatives stay listed.
REFRESHin moq-video,VIDEO_REFRESHin js/publish). CaptureOptionsalready keeps the GOP out of reach, and a ratio is scale-free. Alternatives: (b)encode::Options::refreshplus JSConfig.refresh; (c) a field on the encoderConfigbesidegop.Broadcast.video()track advertises refresh, and the docs state the producer's contract (the encoder is the only producer in the package). Alternative:video(name, { refresh })as an opt-in. That adds API, and a re-registration with a different value could not change the track's fixed info.Kind::Autowith thev4l2feature never advertises, even on a host that picks NVENC or VAAPI. Alternative: create the track inDriver::runafter the probe, when the backend is known. That moves theunique_trackfailure out ofControl::new.Suggested follow-ups
encode::Producer::newin moq-c, moq-ffi, moq-boy) neither advertise nor answer refresh. A small public "a joiner wants a keyframe" query onencode::Producer, plus binding wrappers, would cover them. Recommended as a quest now that decision 1 is confirmed.Checks
cargo test -p moq-video --features capture,openh264 --lib: 266 passed. New:Cutsunit tests,always_cutsagainst the candidate promise, the advertisement perKind, a cut landing on the next frame with no spacing, and a real openh264 capture where a join under the ratio does not cut and a join over it cuts on the next frame, 140 ms after the keyframe.bun test js/publish/src/video/encoder.test.ts: 31 passed. New: cut with no spacing, and a join over the ratio forcing a keyframe 250 ms after the previous one.cargo clippy -p moq-video(default features, andcapture,openh264 --all-targets),tsc --noEmitand biome on js/publish,quest check, andjust checkall pass.just test interop(no wire or ffi change).(Written by Claude Opus 5.5)
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