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feat(mux): cut passthrough groups and sections on the epoch's grid - #5894
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Fallback cuts fall on a one-second grid of the unwrapped PCR timeline the epoch places, and the M2ts section's random_access and mux_rate are judged per two-second window on the same timeline, so importers sharing an epoch publish the same groups and the same section wherever each joined. Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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WalkthroughTS passthrough now selects fallback group starts on a PCR-time grid and publishes catalog sections by PCR window. A new tracker measures mux rates for individual windows. Tests cover window measurements, shared-timebase imports, grid alignment, and catalog publication. The M2 plan removes the raw TS cuts item, revises the catalog audit description, and deletes the related specification. Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to
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The title clearly and concisely describes the main change: aligning passthrough groups and sections to the epoch grid. |
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Docstring coverage is 88.10% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 42 functions across 5 files. (1 skipped: 1 … |
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The pull request description directly explains the epoch-grid group cuts, windowed MPEG-TS metadata, implementation approach, tests, known CI issue, and documented decisions. It is clearly related to … |
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The pull request description directly explains the epoch-grid group cuts, windowed MPEG-TS metadata, implementation approach, tests, known CI issue, and documented decisions. It is clearly related to the changeset.
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The draft and the catalog docs still described the fallback cut as one second from the group's start and randomAccess as latching false for the rest of the track. State the grid on the PCR count, whose wraps follow the catalog clock, the first-group watch, and that randomAccess and muxRate describe the latest two-second window. Pin where a window's edge falls: a layout change before the first PCR past a line counts in the window before. Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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Inline comments:
Review comments at @drafts/draft-lcurley-moq-mpegts.md:
- Line 310: Update the window-publication description to state that the
publisher evaluates each completed window but writes a catalog section only when
its fields change, so consecutive windows with identical values do not create
separate updates.
Review comments at @rs/hang/src/catalog/m2ts.rs:
- Around line 21-23: Update the `random_access` documentation to describe the
multiplex as having at most one video stream and clarify that, when the program
has no video, the clock PID’s random-access indicator can establish random
access.
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doc/concept/hang.mddrafts/draft-lcurley-moq-mpegts.mdrs/hang/src/catalog/m2ts.rsrs/moq-mux/src/container/ts/passthrough.rsrs/moq-mux/src/container/ts/passthrough_test.rs
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…nly program cuts on Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
A joiner whose first PCR lands exactly on a window line can start its first group at a random access point in the PCR interval where its partner already cut on the grid, and so described that window as random access the partner had lost. Describe a window only when it starts strictly after the PCR the first group follows, so every group start in it is one both importers made. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Review comments at @drafts/draft-lcurley-moq-mpegts.md:
- Line 312: Clarify the short-input semantics in the sentence about an input
ending before its first window: specify that randomAccess reflects the carried
content and muxRate, when present, reflects the window in progress, subject to
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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An unflagged repeated PCR exactly on a two-second line left the run's start on the line, so the window holding that empty interval was still measured without its packets. Track whether the window in progress missed an interval instead of where the run began. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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A same-epoch importer joining on the retransmitted copy of a flagged PCR on a grid line left its jump mark empty, so it fallback-cut a second later where its partner, which saw the original, did not. The first PCR's flag now marks the grid like any later jump. Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
A joiner whose first PCR is a flagged jump on a line can miss the flag: the PCR may be a retransmitted copy, or the flag may come in an earlier packet than the PCR. Its partner counted the jump there and skipped the next line's fallback cut, which the joiner made. Counting a flagged first PCR as a jump covered only the retransmitted copy. Requiring the watch to start strictly before the spacing covers both, so that special case goes; an importer whose first PCR lands on a line now waits for the second line after it. Maintainer decision 2026-10-19. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Problem
Two
moq import ts --passthroughinstances sharing one--epochpublish identical objects since#5625, but not identical groups or catalogs. The fallback cut counted
FALLBACKfrom the group'sstart, or from when the importer began waiting, so on a source with no random access points, or
rarer ones than
FALLBACK, each instance kept its own group phase for good. The M2ts section washistory: one non-random-access cut cleared
random_accessfor the importer's life, andmux_ratewas judged on windows starting at the importer's first PCR, with hysteresis. A joiner therefore
published sections its partner never did.
Approach
Per the quest's plan, every group start and both section fields are now a function of the content
and the epoch's timeline, never of when the importer started.
FALLBACKon the unwrapped PCR timeline, the one the epoch places,so a 33-bit wrap does not shift it. The first PCR at or past a line cuts there unless a random access
point or a flagged jump fell in the spacing before the line, each counted at the PCR before it. A
source marking random access more often than
FALLBACKis never cut away from it.point, or a line whose whole spacing the importer watched for random access (from its first PCR
after the PMT). A flagged jump before the first group still starts none, as before; it counts
against the grid either way, since a running partner cut there. Size cuts already counted from the
group's start.
that starts after the PCR the importer's first group follows, the section is written from that window
alone:
random_accesswhen every group it started was a random access point and the layoutallowed random access throughout it;
mux_ratewhen its PCRs arrived unbroken from the window'sstart and its half-second samples agree, rounded to 1 kb/s so PCR jitter does not churn the
catalog. The reservation is held until then, so the first catalog already describes a whole window
its partner described the same way. A new
Windowstype inmux_rate.rsmeasures the rate; thedemultiplexed importer keeps
Meter.carried and the rate of the window in progress, so a short file still lists its track.
Decisions a reviewer may want to revisit: rounding the rate to 1 kb/s (unrounded churns the catalog
every window; hysteresis would bring history back); the 2 s window (the meter's); keeping a jump
before the first group from starting it.
Impact
at it, which a restarted importer's subscribers wait for. The quest asks for it: earlier, a joiner
cannot know a section its partner published. The cost is a supervisor's republish: fix(ts): hold the catalog until the initial mux rate is measured #5287's hold
adds 1.2 s of programme to each one of a demultiplexed import, on a flagged-rewind rig with
--stitch, and this hold should add its own 2 to 4 s to a passthrough one.random_accessrecovers once a window carries only random-access cuts on one program. A relay maystill hold groups from the window that lost it for a while after.
FALLBACKspacings without a random access point (one before),when a random access point falls just after a line.
epoch-anchorandhop-aligned-import.Results
just checkpasses, 3,478 tests.Each new or strengthened test, run against #5625's head with only the tests applied:
importers_sharing_an_epoch_cut_the_same_groups: random access every 1.44 s, none, and two programs on one clock, joined at 2.52, 4.72 and 7.36 s, after a grid cut and (the later two) a recorded rateimporters_sharing_an_epoch_split_full_groups_alike: the object ceiling inside every secondthe_grid_runs_on_across_a_wrap: no random access, joined after the wrapthe_catalog_waits_for_a_whole_windowrandom_access_returns_once_a_window_carries_one_programWindows:a_window_is_measured_alone,a_break_spoils_only_its_own_windowa_joiner_on_a_window_line_describes_the_window_after: the joiner's first PCR exactly on a 2 s line, where the partner cut on the grid just before a random access pointrandom_accesstrue, the partner falsea_joiner_on_a_jump_it_cannot_see_waits_out_the_spacing: the joiner's first PCR is a flagged jump on a 1 s line whose flag it misses, as a retransmitted copy or with the flag in the packet beforets_passthrough_crosses_a_relay_through_a_flagged_jumpwaited for the catalog after one 3 s copyof the capture; its input now carries a copy straight on before the jump, so a whole window passes
first.
the_section_goes_with_the_importerruns on a stream long enough for one window.a_layout_change_before_the_first_pcr_past_a_line_counts_before_itpins the window edge: a PCRinterval belongs to the window it starts in.
CI's one failure on 4345aa4, TS validation's full-multiplex step, is the MP2 join hole
quest/m1/test-flakes-2/ts-mp2-join-hole.mdtracks (PID 0x101, 96 ms at 2.390 s,skipped=120ms),on the demultiplexed exporter's path, which this PR does not touch.
Iteration (quest-iterate)
The maintainer was away, so these calls were made unattended:
for windows starting at or after the PCR the first group follows. When that PCR sits exactly on a
2 s line, the partner may have cut on the grid earlier in the same PCR interval, before the
joiner could start, and the joiner then published random access the partner had lost. Now only
windows starting strictly after it count. The cost is one extra window before the catalog, only
when a first group's PCR lands on a line to the tick.
thread). A PCR interval belongs to the window it starts in, for
random_accessandmux_ratealike, and both importers see it the same way.
random_accessdescribes the latest completed window. It can stay true for up to onewindow after a non-random-access group starts, where the old latch flipped it at once. Nothing in
the repo reads it yet.
Windowskept thestart of the unbroken run, which a repeated PCR exactly on a line left on the line, so that
window was still measured without the interval's packets. It now tracks whether the window in
progress missed an interval (
an_empty_interval_on_a_line_spoils_its_windowfails without it).randomAccessfrom every group it carriedand
muxRatefrom the window in progress (CodeRabbit).first PCR as a jump, which covers a retransmitted flag but not one carried in the packet before
the PCR. The watch before the first group now has to start strictly before a line's spacing, which
covers both, so that special case was removed. An importer whose first PCR lands on a line to the
tick now waits for the line after next (
a_source_without_random_access_groups_every_secondstarts its PCRs at 0, so its first group moves from 1 s to 2 s).
origin/main, including fix(rs): match wasm-bindgen to the nix dev shell's 0.2.129 CLI #5911.Maintainer decisions (2026-10-19)
since + FALLBACK_TICKS < line, with a regression test.Not taken: keeping the mark for a flagged first PCR (f621c6c), or accepting the edge.
randomAccessdescribing the latest completed window. Not taken: clearing it as soonas a non-random-access group starts.
(Written by Claude Opus 5.5)