[kixelated]

Finishes quest/m1/ts-open-gop-trim.md.

Problem

moq-dev/moq#7365 added Mpeg2Picture, a picture-header parser that scanned every MPEG-1/2 video PES the TS export forwarded, to trim open-GOP leading B-pictures after a hole. No consumer asked for it, and decoders already skip those B-pictures. The maintainer picked deleting it on moq-dev/moq#8764.

Approach

• rs/moq-mux/src/container/ts/export.rs: MPEG-1/2 video takes the same path as every other whole PES in Track::queue (straight to push, no leading-picture judgment). Removed Mpeg2Picture, the open_gop and orphan track fields, and its unit test. H.264 open-GOP and HEVC RASL trimming, and RADL keeping, are untouched.
• rs/moq-mux/src/container/ts/recovery_test.rs: removed mpeg2_open_gop_trims_only_the_orphans and the harness support fix(ts): trim open-GOP MPEG-2 leading B-pictures on export #7365 added only for it (the Mpeg2 profile and encoder, the whole-PES video track pickup, the PES-PTS branch of decoded). The Catalog<Ext> republishing and the grader's join-group accounting stay, since they are general.
• doc/bin/ts.md: the semantic recovery bullet says which codecs drop orphaned leading pictures and that MPEG-2 video goes out whole.

Choices made unattended (reviewable): deleting the MPEG-2 recovery profile rather than rewriting its test to assert the B-pictures go out, since its grader models open-GOP orphans as must-trim and the profile existed only to cover the parser.

Impact

• Public API: none. Wire: none.
• Behavior: after a skip, cut, or join, the TS export now forwards an MPEG-2 open GOP's leading B-pictures instead of trimming them; the receiving decoder skips them.

Validation

• just check passes (rs lint and tests for every changed crate, markdown, quest).
• cargo test -p moq-mux --lib container::ts: 761 passed, including every remaining recovery test (open_gop_trims_only_the_orphans, hevc_trims_only_orphaned_rasl, hevc_keeps_radl_after_a_hole) and the MPEG-2 round trips (mpeg2_video_rides_whole_and_survives_a_round_trip, export_resumes_whole_mpeg2_video_at_a_sequence_header).
• Second check of the behavior change: ran the deleted MPEG-2 recovery test from main against the new export. Its grader now fails with video unit 23 went out without the group before it: Unit { group: 2, ..., leading: true, ..., output: true }, i.e. the join group's leading B-picture is forwarded rather than trimmed, as intended.

Alternatives

• Name a consumer that needs the trim and keep the parser: rejected by the maintainer on quest: first pass of the pre-cut feature review, and its follow-ups #8764.

Caused by

• moq-dev/moq#7365 - added a per-frame MPEG-2 picture parser no consumer needed (found by person; the feature review)

Follow-ups

None.

Models

Size: XS
Implementer: Claude, claude-opus-5-5, unknown effort (arm B)

🤖 Generated with Claude Code

Review

Rewritten by quest review after each round.

• Head: b2a93ab

• Base: origin/main at 250a13a

• Risk: medium, the base has no RISK.md to name what is always high or customer-facing, so every change is medium

• Classified: medium by default

• Reviewer: Codex, gpt-6.1-sol, medium effort

• Session: 01a1df49-1709-7852-9e00-a4bbdacbcc55, round 1

• Score: 9/10, Source inspection found no actionable regressions in forwarding MPEG-2 PES whole while preserving H.264/H.265 recovery handling, though builds and tests were not run as instructed.

• Rounds: 1; first round 0; findings 0: fixed 0, refuted 0, open 0

• Findings: none

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Commits

Reviewing files that changed from the base of the PR and between 250a13a and b2a93ab.

Files selected for processing: 4

• doc/bin/ts.md
• quest/m1/ts-open-gop-trim.md
• rs/moq-mux/src/container/ts/export.rs
• rs/moq-mux/src/container/ts/recovery_test.rs

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[pullfrog]

ℹ️ No problems in the code. One follow-up quest still builds on the parser this PR deletes.

Reviewed changes

This review covers how the TS export removes MPEG-1/2 open-GOP trimming, plus the test and doc cleanup that goes with it.

• Track::queue simplified: every kind that isn't Kind::Video now goes straight to push, including whole-PES MPEG-1/2. I checked that Track.held, recovery_gap and leading_floor are only read inside queue's video path. Skipping their updates for MPEG-2 therefore has no effect on anything else.
• Mpeg2Picture and the open_gop/orphan state removed: push's leading check now falls back to false for every kind that isn't video.
• Recovery harness trimmed: Profile::Mpeg2, Video::Mpeg2, the whole-PES video pickup, and the PES-PTS branch of decoded are gone. CLIPS shrinks to 8, which matches the remaining Profile variants indexed by self as usize.
• Docs: the semantic recovery bullet in doc/bin/ts.md now limits trimming to H.264 and H.265.

ℹ️ quest/m5/pes-hold-open-gop.md still plans work on the deleted parser

That quest's goal is to make the MPEG-2 export trim leading B-pictures in zero-stuffed CBR streams. Its plan extends mpeg2_orphans_are_whole_pes_of_leading_b_pictures and builds on the per-track orphan state. This PR deletes all of those. The PR says "Follow-ups: None", but if that quest is left as it is, a later run will pick it up and rebuild what this PR removes. Its second half is still valid, though: H.264 (Open) and HEVC (Rasl) recovery tests have no case with a nonzero join. Since the MPEG-2 arm went away, nothing covers a join at a group already in flight.

Technical details

# Stale follow-up quest after deleting `Mpeg2Picture`

## Affected sites
- quest/m5/pes-hold-open-gop.md — the Goal and most of the Plan target MPEG-2 orphan trimming, which this PR removes. It also names `mpeg2_orphans_are_whole_pes_of_leading_b_pictures` and the per-track `orphan` state, both now gone.

## Required outcome
- No open quest asks for MPEG-2 open-GOP trimming to come back.
- The H.264/HEVC "join at an in-flight group" coverage is kept, either rescoped into this quest or moved to a new one.

## Suggested approach
- Rewrite the quest so it covers only adding a nonzero `join` arm to `open_gop_trims_only_the_orphans` (`Profile::Open`) and `hevc_trims_only_orphaned_rasl` (`Profile::Rasl`) in `rs/moq-mux/src/container/ts/recovery_test.rs`. Alternatively, delete the quest in this PR and file that coverage on its own.

  ^{｜ Fix it ➔ ｜ View workflow run ｜ Using claude-opus-5-5 ｜ 𝕏}