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quest: re-plan TS decode time as one clock with a declared reorder depth - #6390
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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WalkthroughThe decode-order proposal now defines DTS using a declared reorder depth for TS, MKV, and FLV. It describes a shared DecodeClock, producer and importer requirements, exporter validation, and expanded tests. The release-audit documents now point to this work. The shared-parser plan records related rebase and accounting updates. Priority: ⬇️ Low Merge Risk: 🔵 Low · up to
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| Check name | Status | Explanation |
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| Title check |  |
The title names the main change: TS decode time is re-planned as one clock (DecodeClock) with a declared reorder depth. The raw summary and PR objectives both center on the decode-order re-plan around… |
| Description check | |
The description ties directly to the changeset. It explains the re-plan of the 2026-10-22 TS root-cause decisions, the decode-order change from [L] to [XL], the shared DecodeClock for TS, MKV and FLV,… |
| Docstring Coverage | |
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| Linked Issues check | |
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| Out of Scope Changes check | |
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Explanation
The title names the main change: TS decode time is re-planned as one clock (DecodeClock) with a declared reorder depth. The raw summary and PR objectives both center on the decode-order re-plan around a shared DecodeClock and the new reorder field. The title is specific and concise, and it fits the changeset.
Full details: Description check
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Explanation
The description ties directly to the changeset. It explains the re-plan of the 2026-10-22 TS root-cause decisions, the decode-order change from [L] to [XL], the shared DecodeClock for TS, MKV and FLV, the new optional reorder field, deletion of export-reorder folded into decode-order, and the shared-parser ordering against the stream-routes and PAT drafts. It matches the raw summary and objectives.
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No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (4 skipped: 4 unsupported.)
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| - An exporter that reads a frame reordered deeper than its rendition's | ||
| `reorder` refuses the export, never authors an invalid DTS. This bounds the | ||
| clock's held frames by the declared depth whatever the timestamps do, which | ||
| replaces the release audit's export-reorder quest: flat or backward PTS can | ||
| no longer hold frames without bound or drain quadratically. |
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When a hostile publisher supplies an extremely large reorder, retaining up to the declared depth still allows it to make each exporter hold an arbitrary number of frame payloads. The plan replaces the release-audit resource-bound quest without defining any schema/codec maximum or capacity-backed admission check for this network-provided value, so the claimed memory bound is not operationally finite; validate the depth before constructing the clock or tie retention to owned capacity.
AGENTS.md reference: AGENTS.md:L18-L19
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Agreed. Fixed: a reorder above the codec level's MaxDpbFrames (at most 16) refuses, as does a nonzero reorder on a codec that never reorders, so the held frames are bounded by the codec, not by the peer's value.
(Written by Claude Opus 5.5)
| - The depth is a new optional `reorder` field on the Hang video rendition: | ||
| the most frames that can precede a frame in decode order and follow it in | ||
| presentation, the unit of H.264 `max_num_reorder_frames` and HEVC | ||
| `sps_max_num_reorder_pics`. The delay is `reorder` times the frame period | ||
| (the SPS's fixed rate, else the catalog `framerate`). |
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When the SPS has no fixed rate, this derives the constructor's supposedly lifetime-fixed delay from catalog framerate, but rs/hang/src/catalog/video/mod.rs:289-291 defines that value as a maximum and drafts/draft-lcurley-moq-hang.md:1203 explicitly permits it to update in place. Exporters joining before and after such an update can therefore construct clocks with different delays and author different DTS for the same later groups, defeating the quest's central determinism goal; either make the rate/delay immutable identity or remove this mutable input from DTS derivation.
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Agreed. The maintainer chose to drop the time delay entirely: the nth frame of a group decodes at the group's (n - reorder)th presentation slot, and the first reorder frames extrapolate at the group's own slot spacing. No framerate input remains; a test covers a framerate change mid-rendition.
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| authors DTS). Public API and wire: an optional catalog field whose absence | ||
| now means "never reorders", a breaking change for any producer that reorders | ||
| without it; add a `MIGRATE.md` entry for `hang` and `@moq/hang`. |
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The migration work names only hang and @moq/hang, although published moq-mux users also receive a breaking behavior change: a B-frame stream that previously exported without the new catalog field will now be interpreted as reorder = 0 and refused. Add the required rs/moq-mux/MIGRATE.md guidance so direct users know they must populate the new field.
AGENTS.md reference: AGENTS.md:L60-L61
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Agreed. Fixed: the migration entry now covers moq-mux too.
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…migrate moq-mux Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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| - DTS shifts by slots, not by a time: the nth frame of a group decodes at the | ||
| group's (n - `reorder`)th presentation slot, which no frame still to come | ||
| can precede. The group's first `reorder` frames extrapolate below the | ||
| keyframe's slot at the group's own slot spacing. Rejected: a delay of |
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When the first group starts at the common timestamp of zero and declares a nonzero reorder, extrapolating its first decode slots below the keyframe produces negative DTS values. The shared clock and FLV tag timestamps currently use unsigned values, so this cannot be emitted without either saturating multiple frames to zero, shifting DTS after PTS, or rebasing the complete audio/video timeline. Specify that rebasing or another valid representation before making this the common TS/MKV/FLV algorithm.
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Agreed. The clock now works in signed ticks and each exporter maps them to its wire: TS wraps modulo 2^33, MKV writes no DTS and only schedules by it, and FLV rebases its whole audio and video timeline at its first DTS. Never saturate or push a DTS past its PTS. A test covers a group starting at zero.
(Written by Claude Opus 5.5)
| Rust: `rs/hang` catalog; `rs/moq-mux` decode clock, TS/MKV/FLV export, and | ||
| the TS, FLV and fMP4 importers; `rs/moq-video` encoders. JS: `js/hang` | ||
| catalog, `js/publish`. Draft: `drafts/draft-lcurley-moq-hang.md` (the field |
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Add rs/moq-mux's MKV importer to the producer work: it supports H.264/H.265 and forwards blocks in file order with their presentation timestamps, so an MKV containing B-frames can produce the reordered Hang stream that this new field governs. As scoped here, only TS, FLV, and fMP4 importers populate reorder; an MKV-imported rendition therefore leaves it absent and its next TS/MKV/FLV export is required to refuse the reordered frames.
AGENTS.md reference: AGENTS.md:L23-L23
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Agreed. The MKV importer is now a producer: with no decode offsets in MKV, it takes the SPS's declared depth, else the level's MaxDpbFrames.
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Inline comments:
Review comments at @quest/m1/ts-reliability/decode-order.md:
- Around line 61-65: Update the importer fallback described in the producer
rules to derive reorder depth from the complete initial reorder window before
publishing, rather than sampling only the first keyframe; preserve the
SPS-declared-depth path. Add a fixture with a zero-offset keyframe followed by a
nonzero-offset frame and verify the fallback covers that frame.
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| - DTS shifts by slots, not by a time: the nth frame of a group decodes at the | ||
| group's (n - `reorder`)th presentation slot, which no frame still to come | ||
| can precede. The group's first `reorder` frames extrapolate below the | ||
| keyframe's slot at the group's own slot spacing. Rejected: a delay of |
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For a valid stream whose early reference pictures jump over several presentation slots, the bounded clock cannot know the spacing used to extrapolate these initial DTS values. The existing references_far_apart_keep_their_slots fixture in rs/moq-mux/src/container/decode.rs demonstrates this with the conforming depth-2 order 0, 6, 10, 1, ...: when the first frame must be released after reading only the declared lookahead, slots 1 through 5 have not arrived, so the observed gaps are not the group's actual slot spacing. A truncated group may provide no interval at all. Consequently this rule either requires buffering beyond reorder or produces an undefined/wrong initial DTS; specify an independently available spacing or a deterministic fallback that preserves the retention bound.
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Agreed. A group's first reorder frames now step one 90 kHz tick apart up to the keyframe's slot. That needs no spacing, keeps DTS increasing within and across groups without history, holds no frame past reorder, and only relaxes those frames' delivery deadlines; from frame reorder on, each DTS is the real (n - reorder)th slot.
(Written by Claude Opus 5.5)
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…rt-audit-497154 # Conflicts: # quest/m1/release-audit/README.md
SummaryRe-planned the TS decode-time foundation with the maintainer:
Review fixes: slot shift instead of a framerate-derived delay, a level bound on (Written by Claude Opus 5.5) |
Summary
The maintainer re-reviewed the 2026-10-22 TS root-cause decisions (moq-dev/moq#6334). The diagnosis holds: DTS is reconstructed from each exporter's history, and import state has no owner. The re-plan widens and sharpens the decode-time fix.
[L]->[XL]. OneDecodeClockserves TS, MKV and FLV (MKV also used the history-dependentpop; FLV authoredPTS - jitter, which passes the PTS on B-frames). The counted path becomesDecodeClock::new(depth, delay)+pop(flush), andpop_countedgoes away. A new optional Hang video fieldreorder(frames) declares the depth. Absent means 0, so streams without B-frames pay no decode delay. Producers that reorder must set it, and exporters refuse deeper reordering.Public API / wire: none in this PR. decode-order will add the
reordercatalog field, and its absent meaning is a breaking change for producers that reorder.Decisions
Goal: TS stops being patched one symptom at a time; decode time and import state each get one owner shared by every exporter or program, before more support-table rows.
DTS scope:
Reorder constant source:
Ordering vs the open drafts:
Field unit:
Importer that doesn't know the depth up front:
Reopen other audit decisions:
Absent
reordermeans:Field name:
reorderreorderFramesmaxReorderOverlap with release-audit export-reorder:
DTS delay (from review: catalog
frameratemay change in place):reorder)th presentation slotReview fixes also bound
reorderby the codec level'sMaxDpbFramesand add amoq-muxmigration entry.The maintainer also called
pop_counteda confusing name; the plan replaces it with a constructor pluspop(flush).🤖 Generated with Claude Code
(Written by Claude Opus 5.5)