[kixelated]

Summary

Since moq-dev/moq#6757, TS import admits SI only once the program clock has a valid interval, and it places whole PES and sections only between PCRs on that clock. Our export laid out its first slot as PCR, PAT, PMT, then SI and media. A reader learns the clock PID from the PMT, so it can't use that first PCR; anything that needs placing in the first couple of slots was dropped until it repeated. On bbb.ts the re-import counted the first NIT and SDT as unplaced.

The export now opens its timeline: PAT and PMT go first, then a PCR interval (the next two slots' PCRs, one forward step of 25 ms, well within MAX_INTERVAL), then everything the reader places on the program clock.

• Schedule::open (called from build_psi unless the tables continue an earlier program's clock, i.e. a pcr_discontinuity handoff) records the gate: OPENING (2) slots after the slot the first tables finish in.
• Placed units (whole PES and sections) release no earlier than the gate.
• Until the gate's slot is out, the schedule doesn't skip past it, even across a gap after the first frames. The held SI always follows two consecutive PCRs, never a PCR jump the reader can't measure.
• SI muxed while the gate may still be ahead, or while earlier SI is still held (Schedule::clocking), goes to Schedule::push_clocked instead of riding ahead of the frame's PES. The schedule queues it as a late unit in the first slot at or past the gate, so it goes out as soon as it can. Until that unit has fully gone out, later SI is held behind it. The SI keeps the order it was muxed in, even when it spans several slots.
• Decoded audio and video keep their slots, deadlines and pacing. The opening slots are the ones the export already laid; nothing goes out earlier or later than before.

Public API: none. Wire: the first SI and placed PES move a few slots later, after the opening's PCR interval.

Tests

• New export_test::a_reimport_keeps_the_first_si: bbb.ts plus a NIT and SDT, exported unpadded and at 5 Mb/s. It checks that no SI packet precedes the PMT's second following PCR, and that the re-import has no unplaced row, the same PES unit counts as the source, and the NIT and SDT byte-for-byte. It fails without the fix (SI at packet 3, the second PCR at packet 8).
• New schedule::tests::an_opening_holds_placed_units_for_a_pcr_interval and clocked_packets_follow_the_opening_without_the_media: unpadded and padded. Each checks that the held unit goes OPENING slots after the tables while the media keeps its slot.
• New export_test::a_reimport_keeps_the_first_si_across_a_gap and schedule::tests::clocked_packets_follow_the_opening_across_a_gap cover a gap longer than a skip after the first frames. The export test is zero-delay, unpadded and at 5 Mb/s, and checks that the PCR step before the first SI is valid and that the re-import has no unplaced row. The schedule test checks that the slots run 0..=OPENING and that clocking() holds until the SI goes out. Both fail without the fix: the PCR stepped about 3.95 s, and the slots skipped [0, 360]. These cover Codex's and CodeRabbit's findings on the first head.
• New schedule::tests::clocked_packets_stay_ahead_until_they_finish: a 100-packet held SI, unpadded and padded. It checks that clocking() holds until the last packet is out. Without the fix it fails at 16 of 100 out by slot 2. This covers Codex's finding on the second head.
• Updated tests that asserted the old ordering:
  • si_revision_after_final_media_frame_is_flushed: v1 is now found in the slices after the media frame rather than with it.
  • late_join_matches_a_running_exporter_without_video: compares from the PAT refresh after the joiner's held SDT, since the joiner's opening defers its first SDT past the first refresh.
  • Removed the now-unused is_pcr_frame helper.
• just check origin/main passed on the current head: clippy, fmt, rustdoc, and nextest across moq-mux and its dependents (4145 + 126 + 10 tests).

Choices made without asking

• Only what the reader must place waits, not decoded media. I tried holding all media first. Laying the tables two slots early to keep media deadlines made paced exports send the opening slots in one burst; slices_go_out_on_the_clock, a_joiner_runs_at_the_delay_from_its_first_output and a_joiner_keeps_the_system_clock_in_tolerance failed, and a_backlog_stays_in_the_source_until_due timed out. Holding media in place made media that starts near t=0 miss its decode deadlines (late_audio_still_arrives_on_time, a_late_frame_is_dropped_and_the_rest_keep_their_order). Our importer times decoded audio and video by PTS and doesn't need a PCR, so only placed PES/sections and SI wait. See the decision below.
• SI is held aside rather than skipped or placed. Skipping SI until the clock was out lost it entirely in short exports (a_selected_programs_si_survives_export). Placing it at its frame's decode time trailed media that goes out a window early, and that stretched output past a test's drain (repointed_si_entry_resubscribes).
• A program handoff that continues a clock doesn't reopen, keyed on the existing pcr_discontinuity flag. A replacement whose predecessor never got tables out still opens. Schedule::clear keeps a pending opening for that reason. CodeRabbit suggested resetting it; I declined in a comment on the PR.

Decisions

1. Decoded media isn't held (settled by the maintainer, 2026-10-28, taking the recommendation). Ordinary decoded audio and video do not wait for the first PCR; only SI and whole PES/sections are held, as implemented. This narrows the quest Plan's "The first media PES also waits for that PCR": our importer places decoded media by PTS, and holding it would cost either pacing at start or deadlines for media near t=0 (see above).

Follow-ups

None found beyond the decision above.

Closes nothing (the quest lists no issue).

🤖 Generated with Claude Code

(Written by Claude Opus 5.5)

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-28T18:46:03.157386Z	abf2d6d	New commits

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[kixelated]

Automated review by review (OpenAI)
Reviewed commit: 82b9ccb

No actionable bugs found in the changed areas. Holding SI and placed PES/sections until the PMT's following PCR interval is a focused fix; keeping decoded media on its existing schedule avoids unnecessary startup pacing/deadline changes. The scheduling gate and separate SI queue are justified by those different timing requirements, and the padded/unpadded round-trip coverage checks the intended first-emission behavior.

Verification: static inspection of the scheduler, export integration, and regression tests only. I did not run tests or independently verify the reported CI results.

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Walkthrough

TS scheduling now delays placed units and clocked packets until the opening PCR interval has passed. TS export opens the schedule and queues SI bytes while clocking. Tests cover padded and unpadded scheduling, SI export and re-import, including across a media gap, and related output checks. The quest link and design document for SI ordering were removed.

Priority: Normal

Severity of issue fixed: Medium

Merge Risk: Minimal · previous review 25ebd

Initial SI waits for a PCR interval. PCR-PID-changing handoffs can still lose SI, as before; no new merge-blocking risk was found.

Pre-merge checks: 5

Check name	Status	Explanation
Description check		The description clearly explains the MPEG-TS export ordering change, the opening PCR interval, affected scheduling behavior, and validation tests.
Title check		The title is concise and accurately identifies the primary change: placing the first SI after the PMT and a PCR interval.
Docstring Coverage		Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 17 functions across 3 files.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @rs/moq-mux/src/container/ts/schedule.rs:
- Line 1049: Update Schedule::clocking() to remain true while unclocked contains
held bytes, so mux appends later SI revisions to the opening data until it is
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[kixelated]

Automated review by review (OpenAI)
Reviewed commit: a5af3eb

Reviewed the substantive delta from 82b9ccb, separating the main-branch merge. The independently reported opening-PCR gap and held-SI ordering issues are fixed: the pending opening caps the skip target, and clocking remains true while SI is held. My earlier review missed these cases.

No new actionable bugs found in this update. The small scheduler changes preserve the existing design rather than adding another timing mechanism; the padded/unpadded gap tests cover the missed opening sequence.

Verification: static code and test inspection only. I did not run tests or independently verify CI.

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⚠️ Outside diff range comments (1)

Minor · clear() must also reset opening. · schedule.rs:975-976

rs/moq-mux/src/container/ts/schedule.rs:975-976
🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

clear() must also reset opening.

rewind() calls clear(), then sets pcr_discontinuity. A timeline that follows a rewind skips open(). clear() does not reset opening, so a rewind between open() and the first laid slot can leave the flag set. The first slot of the new timeline then consumes it and sets clocked to hold placed units and SI for a PCR interval. The PR states that a pcr_discontinuity handoff does not reopen the timeline, so this hold conflicts with that intent. The effect is a delay of one PCR interval, not data loss.

Reset the flag in clear(), so each timeline decides it through open().

Proposed fix

 		self.lead = None;
+		self.opening = false;
 		self.clocked = 0;
 		self.unclocked.clear();

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Review comment at @rs/moq-mux/src/container/ts/schedule.rs around lines 975 -
976:
Update clear() to reset the opening flag alongside the other timeline state, so
a rewind does not carry an opening hold into the next timeline.

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Review comments at @rs/moq-mux/src/container/ts/schedule.rs:
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[kixelated]

Re CodeRabbit's outside-diff finding on clear() (#7048 (review)): declining. A rewind only runs once the schedule is empty. If opening is still set at that point, the first tables never went out. The reader then has no clock for the next timeline to continue, even though pcr_discontinuity is set. Keeping the flag is what makes that timeline still open. Resetting it would let the first SI go out before the reader can place it. In 25e97be I added a comment in clear() that says this.

(Written by Claude Opus 5.5)

[kixelated]

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(Written by Claude Opus 5.5)

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[kixelated]

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Reviewed commit: 25ebd81

The independently reported deferred-SI tail ordering issue is fixed: the barrier now tracks the queued unit until it drains, and later held SI cannot be enqueued ahead of it. This closes a case my previous review's ordering assessment missed; the opening-PCR gap fix remains intact.

No new actionable bugs found in this delta. Tracking the existing sequence ID is a contained solution without changing media pacing or introducing a second queue scheduler. The new multi-slot test covers the barrier's lifetime.

Verification: static code/test inspection only; tests were not run.

[kixelated]

Merge summary:

• Merged main into the branch as abf2d6d. The only conflict was in the Required link list of quest/m1/ts-reliability/README.md, and the quest merge driver resolved it: this PR's removal of the export-si-order entry plus main's rewritten entries. export.rs and export_test.rs merged cleanly with main's PAT-lifecycle and stitch changes (moq-dev/moq#6689, moq-dev/moq#7049).
• just check origin/main passed locally on the merge: 4160 tests and the full lint set. CI passed on the new head, and Codex reviewed it with no findings.
• quest check --base origin/main passed: this PR finishes export-si-order.md and removes every link to it.
• Settled decision, unchanged: decoded audio and video aren't held behind the opening. Only SI and whole PES/sections wait for the PCR interval.

(Written by Claude Opus 5.5)