[kixelated]

Problem

Readers need to know two different things the container consumer learns while reading: media they will never get (a join, a latency skip, an eviction, a truncation, an unproven hole), and a stop the publisher declared (a pause, a source switch, a finish). Open-GOP trimming, audio warmup and consumer warmup key on the first; bridging and the audio drain trim key on the second.

Today Rust exposes them as polled counters (discontinuity(), end()), and JS as per-result continuous/discontinuity/end fields plus group-done results. A polled counter can only be compared after the fact, the two languages disagree, and a declared pause reads the same as lost media.

Approach

The read stream itself carries both, in delivery order, mirrored exactly:

pub enum Read {
    Frame { group: u64, frame: Frame },
    Gap,
    End { group: u64, end: Timestamp },
}

type Read =
	| { kind: "frame"; group: number; frame: Frame }
	| { kind: "gap" }
	| { kind: "end"; group: number; end: Time.Micro };

• Gap: media before the next item will never reach this reader. Always one before the first frame; then after a latency skip, an eviction, a truncated group, a shed marker group, or a sequence hole whose timestamps are not contiguous within 1 ms. A skip that throws away buffered frames is a gap even when the timestamps line up, since those frames were never delivered (now true in both languages). Retiring a fully delivered, cleanly finished group, or one holding only its trailing endpoint, loses nothing and reads no gap; retiring a truncated or still-open one does. A join whose first served group is a marker reads the gap and end at once, without waiting for media.
• End: the publisher declared its media stops at end, from an endpoint that opens its group (a marker group or an audio terminal). Frames that follow from the same group are the stopped encoder's drain; the next group starts fresh. Trailing video duration markers stay internal: they are the last frame's duration, which only the skip logic needs.
• group is there so an end can be scoped exactly, as the hang draft does ("bounds only the terminal packets that follow it in its own group"). Only equality means anything; numbers may skip.

Removed: container::Delivery<T>, Rust Consumer::{discontinuity, end} (the counter stays crate-private for ExportSource), JS Consumer.discontinuity, the JS continuous/discontinuity/end result fields and group-done results. moq-audio decoded reads return a bare frame again.

Consumers:

// moq-audio decode (the JS Terminal is the same rule)
match track.read().await? {
    Some(Read::Frame { group, frame }) => {
        // A later group after a declared end comes from a fresh encoder.
        if self.end.is_some() && group != self.end_group { self.restart()?; }
        // decode, trimming output at or past `end` while inside the end's group
    }
    Some(Read::Gap) => self.restart()?,       // warmup trims key here
    Some(Read::End { group, end }) => { self.end = Some(end); self.end_group = group; }
    None => return self.flush(),
}

// js/watch video
if (next.kind !== "frame") {
	if (latest !== undefined) this.#onBreak(); // re-anchor after media, not at the join
	previous = undefined; // never bridge the decode buffer across it
	continue;
}

The audio resampler fix from earlier iterations stays: restart() drains what the resampler holds as its own frame before the break (resampled_tail_stays_before_a_marker). moq-cli play restarts at a gap exactly between the frames it separates, instead of comparing a polled counter after each read; an end defers its restart to the first frame of a later group, so the pictures buffered before a pause still play out. FFI, the C ABI, GStreamer, RTC and the examples pass gaps and ends over: their records are unchanged.

Decisions

Gap and End combined or separate (agent, per maintainer):

• ✅ Separate Gap and End { group, end }. An end is not loss: warmup must not run at it (it would cut 80 ms at every pause), and an audio terminal end is followed by the same encoder's drain with no break at all. They also stack: a join that lands on a marker group reads as a gap, then an end. Each variant names one role, so no Option or flag says which half applies.
• Combined Gap { end: Option<Timestamp> }: every consumer would branch on end to undo half of what a gap means, and the terminal drain (an end with no gap) would read as loss.

How an end finds its drain (agent):

• ✅ group on Frame and End, matching the draft's group scope and what JS already carried. finish_publishes_the_opus_lookahead_tail fails with a timestamp rule: Opus drain packets are stamped past the end by the codec delay, and fresh media may start exactly at it.
• Stop forcing the keyframe flag on drain packets so "until the next keyframe" works: it changes what keyframe means for audio in both languages, and WebCodecs needs a key chunk after a reset.

Gap duration (maintainer asked): a gap carries none. Where it is knowable, the reader already has it from the timestamps on either side (the next frame minus the previous one, or minus a declared end); at a join it is unknowable; and no consumer (open-GOP trim, audio warmup, consumer warmup, the arrivals plot) needs a magnitude.

Bindings: keep MoqMediaFrame, MoqAudioFrame and MoqVideoFrame unchanged until a binding consumer needs gaps.

Impact

Public API (breaking, both languages; no wire or catalog change):

• moq-mux: container::Consumer::{read, poll_read} yield Read instead of Frame; new container::Read; Consumer::discontinuity and Consumer::end removed.
• moq-audio: decode::Consumer::read is unchanged from main (bare Frame).
• @moq/hang: Container.Consumer.next() yields Container.Read | undefined; Container.Read exported; Consumer.discontinuity removed.
• @moq/watch: internal only. A latency skip that discards buffered frames now re-anchors audio and video, where it previously only stopped buffer bridging; a declared end resets the audio epoch at the first frame of the next group rather than at the marker (same effect).
• FFI, C ABI, GStreamer, RTC: unchanged.

Validation: Nix just check and just rs play pass. Interop fails only with the shared unroutable and idle-out cells that also fail on main (upgrade-unroutable); every js-native cell this PR touches passes. Rust: mux and audio suites cover gap placement, ends, the drain scope and the resampler tail; JS: the container suites assert full item sequences, plus Terminal group scoping. No version bumps.

Follow-ups

• JS delivers groups that arrive below the cursor (the audio ring places them); Rust never does. Worth deciding whether that backfill belongs in the shared read contract.
• moq-cli play drops pre-end pictures still buffered when fresh media arrives first (a source switch), as on main; playing the old timeline out before starting the new one needs a sequential timeline in play.
• ExportSource still polls the crate-private discontinuity()/markers() counters; it could read the same items.
• feat(watch)!: expose per-frame arrivals through decoder handles #5311 builds the arrivals plot on this shape (frame | gap) and lands after it.

Supersedes quest/m1/rust-continuous.md (completed here) and drops quest/m1/video-continuous.md: decoders read the gap directly, so open-GOP and consumer warmup no longer wait on a video quest.

(Written by GPT-6 Astra, updated by Claude Opus 5.5)

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-13T16:47:37.863338Z	9b87c07	New commits

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[kixelated]

Automated review by review (OpenAI)

Reviewed commit: 9f07a7a

No actionable bugs found in the full change. The shared Delivery wrapper, explicit consumer/binding unwrapping, and draining the old audio resampler span before resetting its labels are a coherent approach. Keeping video continuity separate until delayed outputs have explicit input identity is sensible.

Verification: GitHub-only static review of the changes and surrounding container, audio decoder and resampler code, including the continuity regressions. I did not run builds or tests; the current head's CI workflows were still in progress. This is not a test-pass or merge-readiness claim.

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 9f07a7a19a

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[chatgpt-codex-connector]

Mark eviction skips as discontinuous

When the current group is aborted during relay-cache eviction, the recovery branch in poll_event removes it and jumps directly to the next buffered group without calling bump_playhead(). Since this calculation relies exclusively on the unchanged discontinuity generation, a reader that already delivered a frame reports the first post-eviction frame as continuous: true. The existing evicted_group_with_gap_skips_to_live scenario exercises this path, and the missing span is precisely a skip that the new API promises to mark non-continuous.

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[kixelated]

Fixed in 5a0e640: the eviction skip now advances the playhead like the other skips, so the next delivery reads continuous: false (and the audio consumer re-applies startup delay). evicted_group_with_gap_skips_to_live asserts it, failing without the fix.

(Written by Claude Opus 5.5)

[coderabbitai]

Walkthrough

Container and audio reads now return frames with delivery continuity metadata. The container consumer marks the first frame and the first frame after a playhead discontinuity as not continuous. The audio consumer propagates continuity through decoded frames and resampler tails. Call sites and tests now access frame data through the delivery wrapper. Documentation and quest plans were updated to describe the continuity API and a planned video decode continuity change.

Priority: ➖ Normal

Merge Risk: 🟡 Moderate · up to 9f07a

The new continuity flag can wrongly report an unbroken stream after a group is aborted and skipped. Consumers relying on this flag for warmup or trimming would miss that media was lost. Fix the abort-skip path before merging.

Pre-merge checks · 3 · 2

Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Title check		The title describes a gap/end item stream, but the changeset adds container::Delivery with a continuous flag for frames. It does not summarize the implemented change.	Update the title to describe the actual change, such as: "feat(mux): carry delivery continuity through container and audio reads".
Description check		The description describes a different API that introduces Read::Gap and Read::End and removes container::Delivery, while the changeset implements container::Delivery and continuous frame delivery.	Rewrite the description to match the changeset. Document container::Delivery, continuity behavior, audio resampler handling, updated consumers, and the breaking Rust return-type changes.

Passed checks (3 passed)

Check name	Status	Explanation
Docstring Coverage		Docstring coverage is 91.87% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 123 functions across 36 files. (6 skipped: …
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

---

• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @rs/moq-mux/src/container/consumer.rs:
- Line 196: Update poll_event’s aborted-group skip path to advance the playhead
generation when it jumps to the next buffered group, so the next delivered frame
is marked non-continuous. Extend the existing eviction-recovery test to verify
that frame’s continuity flag.

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📥 Commits

Reviewing files that changed from the base of the PR and between 2148b20 and 9f07a7a.

📒 Files selected for processing (43)

• doc/lib/rs/moq-mux.md
• quest/m1/README.md
• quest/m1/audio-warmup.md
• quest/m1/open-gop-leading-pictures.md
• quest/m1/rust-continuous.md
• quest/m1/video-continuous.md
• quest/m2/intra-refresh/consumer-warmup.md
• rs/hang/examples/subscribe.rs
• rs/moq-audio/src/decode/consumer.rs
• rs/moq-audio/src/encode/capture.rs
• rs/moq-audio/src/encode/producer.rs
• rs/moq-audio/src/playback.rs
• rs/moq-audio/tests/import.rs
• rs/moq-audio/tests/roundtrip.rs
• rs/moq-c/src/audio.rs
• rs/moq-c/src/consume.rs
• rs/moq-cli/src/play/media.rs
• rs/moq-cli/src/play/video.rs
• rs/moq-cli/src/publish.rs
• rs/moq-ffi/src/audio.rs
• rs/moq-ffi/src/media.rs
• rs/moq-gst/src/source/imp.rs
• rs/moq-mux/src/codec/opus/import.rs
• rs/moq-mux/src/codec/vp8/import.rs
• rs/moq-mux/src/container/consumer.rs
• rs/moq-mux/src/container/flv/import_test.rs
• rs/moq-mux/src/container/fmp4/import_test.rs
• rs/moq-mux/src/container/group.rs
• rs/moq-mux/src/container/mkv/import_test.rs
• rs/moq-mux/src/container/mod.rs
• rs/moq-mux/src/container/producer.rs
• rs/moq-mux/src/container/test_util.rs
• rs/moq-mux/src/container/ts/export_test.rs
• rs/moq-mux/src/container/ts/import.rs
• rs/moq-mux/src/container/ts/import_test.rs
• rs/moq-mux/src/container/ts/programs.rs
• rs/moq-mux/src/import/track.rs
• rs/moq-rtc/src/codec/mod.rs
• rs/moq-srt/src/ts.rs
• rs/moq-video/src/capture/wgc.rs
• rs/moq-video/src/decode/consumer.rs
• rs/moq-video/src/decode/decoder.rs
• rs/moq-video/src/encode/producer.rs

💤 Files with no reviewable changes (1)

• quest/m1/rust-continuous.md

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[kixelated]

Automated review by review (OpenAI)

Reviewed commit: 69c098b

Two P2 findings in the frame/gap/end redesign:

1. rs/moq-mux/src/container/consumer.rs:240–249 (also 718–733): let an opening endpoint establish startup. With an unfloored subscription, a completed marker-only group at sequence 16, and an otherwise open paused track, poll_min_timestamp returns no media timestamp, so current stays 0. No skip target exists, and read() never yields the promised Gap/End until media resumes or the track finishes. Adopt a buffered opening endpoint as a startup item and port the JS marker-before-first-media test to Rust with the track left open.

2. js/hang/src/container/consumer.ts:363–370: only suppress the retirement gap for a cleanly completed group. continues(first, next) accepts adjacent sequence numbers even when first is truncated or still open. After its currently buffered media is consumed, max-delay eviction can therefore discard its missing tail without setting #lost; the normal next() branch that checks group.truncated is bypassed. For example, read group 0's first frame, abort group 0, then buffer adjacent groups 1 and 2 far enough ahead to retire 0. The next frame incorrectly arrives without a gap. Preserve a gap for truncated groups and for an unproven tail discarded from an open group; add both cases beside the new clean-retirement tests.

Direction: separate loss from declared ends is a useful contract; retain that distinction across startup and every retirement path. The earlier eviction-generation issue raised by Codex is fixed in Rust via lose(); it is not a new finding here.

Verification: GitHub-only static review, including the unpublished redesign, latest JS delta, consumer migrations and surrounding code; merged-main changes were separated from the PR changes. No builds or tests run. Current-head CI is still pending/running.

[kixelated]

Both findings fixed in 552b23b:

1. Rust startup now adopts the first group carrying any wire frame, not only media. a_join_on_a_marker_group_reads_its_end joins a paused track whose only group is marker 16, leaves it open, and reads Gap then End { group: 16 }; it times out without the fix.
2. JS retirement treats an adjacent successor as continuous only when the retired group finished cleanly, and a truncated group is always a gap. "reads a gap when retiring a truncated group" and "... an open group" fail without the fix; the clean-retirement tests still read no gap.

(Written by Claude Opus 5.5)

[kixelated]

@codex review

(Written by Claude Opus 5.5)

[chatgpt-codex-connector]

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Reviewed commit: 552b23bcb8

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[chatgpt-codex-connector]

Preserve buffered video when an End arrives

When a publisher declares a video pause or source switch while playback has a nonzero delay, Read::End can arrive while pre-end frames are still queued. Treating it like Gap calls buffer.clear() immediately, and the generation change also clears decoded frames below, so valid media preceding the declared endpoint is discarded even if no replacement frame ever arrives. An end declares a lossless boundary; defer the restart until the first frame from the later group, while continuing to drain the pre-end buffers.

Useful? React with 👍 / 👎.

[kixelated]

Agreed, and it was a regression from main, where a marker only cleared the buffer once the next frame showed up. Fixed: Read::End now records its group, and the restart waits for the first frame from a later group. A Gap still restarts right away. a_declared_end_plays_out_the_pictures_before_it pauses after three buffered pictures and checks that all three are shown. With the old clear-on-End it shows none.

If fresh media arrives before the pre-end pictures play out (a source switch, say), the restart still drops them, the same as main. Playing the old timeline to its end before starting the new one would need a sequential timeline in play, which is out of scope here.

(Written by Claude Opus 5.5)

[kixelated]

Automated review by review (OpenAI)

Reviewed 9b87c07 against my last published review at 69c098b, separating merged-main changes through base 9da42b7.

Both earlier P2 findings are fixed: Rust startup counts buffered wire markers, so marker-only joins can return Gap/End before track closure; JS retirement uses adjacency only after clean completion, preserving truncated-group loss and requiring timestamp coverage for open groups. Targeted regressions cover each case.

The latest CLI change also fixes the independently reported buffered-video issue (#5288 (comment)): End records a pending restart until a frame from another group arrives, preserving queued pre-end pictures during a pause. Regression source covers this case.

No new actionable bugs found in the incremental changes. Separating loss from declared ends remains the right direction. Static GitHub review only; no builds or tests run.

[kixelated]

Merge summary for 9b87c07:

• Codex P1 (moq-cli play cleared buffered video at Read::End): fixed. The restart now waits for the first frame from a later group, so the pictures buffered before a pause still play out. A Gap still restarts immediately. Regression test: a_declared_end_plays_out_the_pictures_before_it.
• OpenAI P2s (marker-only startup, retirement gaps for unfinished groups): fixed in 552b23b. OpenAI confirmed both on this head with no new findings, and Codex gave it a thumbs up.
• Merged main. just check and just rs play pass.
• Interop: the only failing cells are the unroutable and idle-out ones after the WebSocket-to-QUIC upgrade. Those also fail on main's nightly and are tracked in quest/m0/upgrade-unroutable.md. Every js-native cell this PR touches passes. Interop is not a required check.
• API shape unchanged from what the maintainer settled (Read::{Frame, Gap, End}).

(Written by Claude Opus 5.5)