feat(mux): export ts --passthrough writes the m2ts track back on a fixed delay

[t0ms]

Implements the mode that the TS passthrough export quest plans: the export half of #5003's passthrough import. It does not retire the quest. #5327 rewrites that quest's acceptance, and this PR meets part of it (listed below). It touches no quest file, so it does not conflict with #5327.

moq export ts --passthrough --delay <dur> reads the track named by the catalog's m2ts section. From the first group it releases, it writes that track's packets back out unchanged. Each object (the packets from one PCR to the next) goes out --delay after its PCR time on the TS export's jitter buffer. The output therefore keeps the source's PCR pacing, and two exporters write the same bytes. An object past its deadline is dropped and counted, which leaves a continuity error. A flagged forward jump opens a new clock instead of being waited out. --passthrough conflicts with --linger, --stitch and --mux-rate, and doc/bin/cli.md documents the flag. Only the hang catalog carries the m2ts section, so Release::new refuses CatalogFormat::Msf rather than wait forever; an .msf broadcast needs --catalog-format hang.

Tests (rs/moq-mux/src/container/ts/release_test.rs, run on in-repo captures):

• a_capture_is_released_byte_identical_on_its_own_pcr: from the first released group, the output is the input, in order. Each object goes out within 1 ms of its PCR time.
• releases_fed_with_different_skew_write_the_same_bytes
• an_object_past_its_deadline_is_a_gap_in_that_release_only: late objects are counted and are missing from that release only. The rest go out on their PCR schedule.
• a_flagged_jump_crosses_without_holding_the_output
• an_msf_catalog_is_refused

Each release drains in its own task, so one waking never polls another. Under tokio::join! the stalled release was polled whenever the steady one woke, which hid a late object being timed by the last empty poll instead of its read.

Against the quest as #5327 rewrites it, this covers four of its checks: byte and packet-order identity from the first released group on a complete path, the release schedule, identical output from releases fed with different skew, and a missed deadline. It leaves:

• the T-STD verdict on output and input as a CI test (checked by hand below);
• the fixture set (null and unknown PIDs, split PES, clock wrap, an MPTS with unaligned program recovery points), explicit accounting of the importer's acquisition prefix, and a reusable packet-position and release-schedule oracle (the helpers here are local to the test);
• deterministic group omissions, including counting them. dropped counts objects that arrive late, but a group the relay ends never arrives, so it is logged and not counted;
• automated TSDuck and FFmpeg runs, and the nightly impairment test.

On real captures (manual grading, which #5327 treats as supplementary): loopback on a dedicated Linux host, --delay 1s, 120 s, two subscribers, one joining 8 s late, graded with this repo's test/ts tools.

	CNN International (passes the strict T-STD)	TNT Sports 4 cut (fails it)
Output against the source	every packet in order, 0 gaps, 0 dropped	the same
Late leg against the first, over their overlap	identical (125 MB)	identical (302 MB)
compliance.py tstd, output / source span	pass / pass	fail / fail, identical detail
pcr-timing.py --live pcr-release-timing	0 of 4,380 outside ±10 ms, worst 1.8 ms	0 of 4,179, worst 1.9 ms
pcr-rate	−0.13 ppm	+0.16 ppm

The #4613 rig (10 % loss on the relay-to-subscriber link, 25 ms each way, BBRv3 on noq, 120 s): no process died, and the output is only source bytes, with each gap a whole number of groups. It delivers about 6 % of the video. The relay ends most group streams as Old, and the consumer logs each one (current group evicted). This is not specific to passthrough. Graded on content, the demultiplexed export ts --delay of the same build delivers 3.5–8.2 % of the video in the same rig, with 90–95 % of its output null packets, and --delay 6s helps neither export.

just check passes.

(Written by Claude Opus 5.5, updated by Claude Opus 5.5 for the review fixes)

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-12T14:47:50.723268Z	0da3a77	PR opened

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[kixelated]

Automated review by review (OpenAI)

Reviewed commit: 0da3a77

No actionable bugs found in this review. The dedicated passthrough release path is a sensible, small addition: it reuses the existing catalog subscription, group consumer and jitter clock while leaving packet payloads untouched. I checked the CLI wiring and conflicts, acquisition and late-drop behavior, discontinuity handling, end-of-track draining, and the added tests against the surrounding importer and buffer code.

Verification limits: source review through GitHub only; I did not run builds, tests, or the manual TS compliance experiments. The explicitly deferred whole-group omission accounting and broader conformance/impairment fixtures remain coverage gaps, so this does not establish full quest acceptance.

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📒 Files selected for processing (5)

• doc/bin/cli.md
• rs/moq-cli/src/args.rs
• rs/moq-cli/src/main.rs
• rs/moq-mux/src/container/ts/release.rs
• rs/moq-mux/src/container/ts/release_test.rs

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Walkthrough

The change adds PCR-timed release of MPEG-TS passthrough frames with a configurable delay and late-frame counting. The CLI gains a --passthrough option that selects this release path for TS export and writes released payloads to stdout. The change also adds tests for replay timing, PCR discontinuities, arrival skew, and stalled delivery, and documents timing behavior and incompatible options.

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to 75379

TS passthrough export is wired through the CLI, with no identified issue requiring a fix before merge.

Pre-merge checks · 4 · 1

Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 73.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 30 functions across 6 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the primary change: adding fixed-delay MPEG-TS passthrough export.
Description check		The description is directly related to the changeset and explains the new passthrough mode, behavior, constraints, tests, and remaining scope.
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 73.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 30 functions across 6 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 1

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Inline comments:
Review comments at @rs/moq-mux/src/container/ts/release.rs:
- Around line 119-140: In Release::poll_next, set Arrival::arrived to the
current read timestamp so late passthrough objects are detected correctly.
Remove the obsolete self.empty field and its initialization and updates when
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📒 Files selected for processing (7)

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• rs/moq-cli/src/subscribe.rs
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• rs/moq-mux/src/container/ts/release.rs
• rs/moq-mux/src/container/ts/release_test.rs

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[kixelated]

Automated review by review (OpenAI)

Reviewed commit: 75379e9

No new actionable bugs found. Both independently reported issues are fixed: late objects use their read timestamp, with independent release tasks preventing the regression test from masking the bug, and MSF is rejected before catalog subscription, with a refusal test. The main merge leaves the passthrough implementation unchanged.

The dedicated release path remains a reasonable scoped addition, reusing catalog discovery and clock recovery without rewriting payloads. Whole-group omission accounting and broader conformance/impairment coverage remain explicitly deferred; this does not establish full quest acceptance.

Verification: GitHub source review only. I did not run builds, tests, or manual capture experiments.

(Written by OpenAI)

[kixelated]

Merge summary. Review fixes in 6d8dc5a:

• Release times each object by its read rather than by the last empty poll, so an object landing past its deadline is dropped and counted instead of going out late. The stall test now drains each release in its own task, which is what had masked this under tokio::join!.
• Release::new refuses CatalogFormat::Msf, which carries no m2ts section, rather than waiting forever. Refusing was chosen over forcing hang so that an explicit --catalog-format msf is not silently overridden. doc/bin/cli.md says an .msf broadcast needs --catalog-format hang.

Main is merged in, including #5305; its doc/bin/cli.md and args.rs changes merged cleanly alongside --passthrough. OpenAI reviewed this head with no findings. Local just check passes. Enabling auto-merge pinned to 75379e9.

(Written by Claude Opus 5.5)