open-standards/wai/extensions/packaging.md

# WAI Extension: Packaging

> Status: Draft. A packager turns sources into WAI objects under a declared policy;
> this extension fixes what a verifier recomputes. This revision defines the policy,
> its digest and what it may ask a packager to emit (§3), how a source is cut into
> pieces (§4), the objects a packager writes, refinements and stills among them, and a
> piece's ladder (§5), the stage index (§6), the floor, one or several, supplied as OBU
> streams or as an existing ladder's CMAF files (§7), what each class is offered
> over HTTP and MoQ and how its delivery is simulated (§8), the package receipt and live
> windows (§9), the package, its verification and a re-pack from a parent (§11), and
> where each step of a pack or a verify may run (§11.6).
> Reference impl: `wai-pack` —
> `policy`, `capcheck`, `source`, `scenecut`, `classify`, `plan`, `encode`, `png`,
> `floor`, `cmaf`, `cmaf_read`, `catalog`, `files`, `pack`, `live`, `delivery`, `verify`,
> `fabric`, `fabric_meter`, `floor_decode`, and `wai-pack-gpu` for the steps a GPU runs;
> in `wai-rs`, the
> encoder `int_video_enc`, the refinement encoder `staged::wir1`, the stage index
> `stage_index`, the receipt `package` and the delivery simulator `stage_measure::sim`;
> the corpus [`pack-conformance/`](../pack-conformance/). Keywords **MUST**, **MUST NOT**,
> **SHOULD**, **MAY** are RFC 2119/8174.

## 1. Scope

A **packager** turns one or more sources into WAI objects, stage indexes, catalogs
and a package receipt, under a declared **policy**. This extension fixes what a
package contains and what a verifier recomputes. It fixes an encoder's choices only
where it names them.

## 2. Terms

- **Component**: one media stream of a package (for example video, or audio).
- **Piece**: a span of a component that decodes with no reference outside itself.
- **Stage**: one object of a piece in staged order: the base is layer 0, refinement
  *k* is layer *k* ([staged-delivery](staged-delivery.md)).
- **Rung**: one entry of the policy's ladder: a capability a component's pieces are
  coded in, with its role (base, refinement or floor) and parameters.
- **Class**: a delivery profile the policy names.
- **Moment**: a declared span of presentation time with tags.
- **Floor**: a rendition in a standard codec, for sinks that lack the primary.
- **Floor name**: the name a floor rung's files and catalog entries carry (§7.1): its
  component's id when the component has one floor rung, the rung's id when it has
  several.
- **Timebase** of a component: `num / den` units per second. For video one unit is
  one frame; for audio, one sample.
- **Step**: one of the computations of a pack or a verify (§11.6), such as the base's
  motion search or an object's content hash.
- **Fabric**: the kind of processor a step runs on: `cpu`, `gpu`, `media` (a hardware
  video engine) or `npu` (a neural processor) (§11.6).

## 3. Policy

**3.1** A package is made under exactly one policy, a TOML 1.0 document of schema
`wai.pack.policy/1`, in UTF-8 with no byte-order mark.

**3.2** The **effective policy** is the policy with every default written in (§3.3)
and every override the packager applies (such as a command line forcing
`royalty_free_only`). An override only ever forces `royalty_free_only` on; it never
turns off what the policy asks for. Its JSON form is §3.3's members, with an optional member that
has no default omitted when absent, and arrays of tables in document order. Its
**policy digest** is

    BLAKE3("wai:pack-policy\x01" ‖ JCS(effective policy as JSON))

where JCS is RFC 8785. Two spellings of one policy (member order, inline or standard
tables, dotted keys, string or integer notation, comments, an omitted default or the
default written out) therefore have one digest; the order of an array of tables is
part of the policy.

A packager **MUST** refuse with `policy-toml`, before anything else, a policy whose
bytes are not UTF-8, that begins with a byte-order mark, that is not TOML 1.0 (an
integer outside TOML's 64-bit range included), or that nests arrays and tables more
than 32 deep: the document's own table is at depth 1, and an array or a table
directly inside one at depth *k* is at depth *k* + 1. Then, before it reads any key, it
**MUST** refuse one holding anywhere a float (`policy-float`), a date or time
(`policy-datetime`), a negative integer (`policy-negative`), or an integer above
`2^53 − 1` (`policy-integer-range`), visiting members in byte order of their keys and
arrays in order.

**3.3** *Schema.* Within each table, a key this section does not define is refused
first (`policy-unknown-key`, the first in byte order), then each member in the order
listed: a required member that is absent (`policy-missing-key`), a member of another
type (`policy-type`), a value outside its range or vocabulary (`policy-value`). An
absent table reads as empty.

| Member | Type | Default | Range |
|---|---|---|---|
| `schema` | string | required | `wai.pack.policy/1` (else `policy-schema`) |
| `asset_id` | string | required | 1 to 255 bytes |
| `royalty_free_only` | boolean | `false` | |
| `lead` | string | required | 1 to 255 bytes |
| `component` | array of tables | required | |
| `component.id` | string | required | 1 to 255 bytes |
| `component.media` | string | required | `video`, `image`, `audio`, `world`, `feed`, `avatar`, `film` |
| `component.source` | string | absent | |
| `component.timebase` | table | required | members `num`, `den`, each 1 to `2^32 − 1`, required |
| `component.profile` | string | absent | `floor-only` (§7.8); absent, the standard profile |
| `segmentation.target_ms` | integer | 2000 | |
| `segmentation.min_ms` | integer | 1000 | |
| `segmentation.max_ms` | integer | 4000 | |
| `segmentation.scene_cut` | string | `wai.pack.scenecut/1` | `wai.pack.scenecut/1` |
| `segmentation.cut_abs_permille` | integer | 300 | 1 to 1000 |
| `segmentation.cut_rel_permille` | integer | 3000 | 0 to 1000000 |
| `segmentation.cut_window` | integer | 8 | 3 to 64 (a window of fewer than 3 scores never applies `cut_rel_permille`, §4.3) |
| `segmentation.lookahead_frames` | integer | 6 | 0 to 64 |
| `segmentation.closed` | boolean | `true` | |
| `ladder` | array of tables | empty | |
| `ladder.id` | string | required | 1 to 255 bytes |
| `ladder.component` | string | required | 1 to 255 bytes |
| `ladder.capability` | string | required | |
| `ladder.role` | string | required | `base`, `refinement`, `floor` |
| `ladder.refines` | string | absent | |
| `ladder.params` | table | empty | by capability, below |
| `floor.supplied_listing` | string | absent | 64 lowercase hexadecimal digits |
| `floor.extra_keyframes` | boolean | `false` | |
| `floor.supplied_form` | string | absent | `cmaf` (§7.7); absent, the OBU form (§7.3) |
| `live.layer_lag_ms` | array of integers | one 0 per layer | §3.4 |
| `class` | array of tables | empty | |
| `class.id` | string | required | 1 to 255 bytes |
| `class.max_layer` | integer | 0 | 0 to 255 |
| `class.max_kbps` | integer | absent | 1 to `2^32 − 1` |
| `class.floor_only` | boolean | `false` | |
| `moment` | array of tables | empty | |
| `moment.id` | string | required | 1 to 255 bytes |
| `moment.from_ms`, `moment.to_ms` | integer | required | `to_ms` above `from_ms` |
| `moment.tags` | array of strings | empty | |
| `rule` | array of tables | empty | |
| `rule.id` | string | required | 1 to 255 bytes |
| `rule.when.piece_kind` | array of strings | absent | `natural`, `static`, `synthetic`, `motion_high` |
| `rule.when.moment_tag` | array of strings | absent | |
| `rule.then.ladder` | array of strings | absent | |
| `rule.then.max_layer` | integer | absent | 0 to 255 |
| `rule.then.deadline_ms` | integer | absent | 1 to `2^32 − 1` |
| `defaults.deadline_ms` | integer | 1500 | 1 to `2^32 − 1` |
| `classify.static_permille` | integer | 5 | 0 to 1000 |
| `classify.static_mad_milli` | integer | 300 | |
| `classify.synthetic_bins` | integer | 12 | 0 to 64 |
| `classify.motion_high_milli` | integer | 9000 | |

A rung's `params` are those of its capability; every other capability takes none.

| Capability | Parameter | Default | Range |
|---|---|---|---|
| `wai.video.int_motion` | `block` | 16 | 4, 8, 16, 32 |
| | `search` | 7 | 0 to 32 |
| | `mv_precision` | 2 | 1, 2 |
| | `q_candidates` | `[8]` | a non-empty array, each 1 to 255 |
| | `max_sse_px_milli` | 0 | |
| `wai.video.int_refine` | `q` | required | 1 to 255 |
| `wai.video.av1`, `wai.video.av1.lossless` | `source` | `supplied` | `supplied`, `encode` |
| `wai.audio.int_refine` | `to_rate`, `q` | required | 1 to 384000; 1 to 65535 |
| `wai.audio.flac` | `source` | `encode` | `encode`, `supplied` |

`wai.audio.int_layered` is reserved for the layered integer audio base: it is not
registered yet, and its parameters are defined when it is.

**3.4** *Constraints.* A policy that passes §3.3 is checked in this order, and the
first that fails is the refusal:

1. 1 to 8 components (`policy-too-many-components`); at most 64 rungs
   (`policy-too-many-rungs`), 32 classes (`policy-too-many-classes`), 32 rules
   (`policy-too-many-rules`) and 32 moments (`policy-too-many-moments`).
2. Ids unique among components, rungs, classes, moments and rules taken together, so
   a reference never names two things (`policy-duplicate-id`).
3. `lead` names a component (`policy-lead`).
4. `segmentation.closed` is true: every piece is closed, §4.1 (`policy-open-gop`).
5. `1 ≤ min_ms ≤ target_ms ≤ max_ms ≤ 600000`, and `max_ms` is at most `2^24` units
   on every component's timebase (§4.4) (`policy-piece-bounds`).
6. Every rung names a component (`policy-ladder-component`).
7. A rung carries `refines` exactly when its role is `refinement`
   (`policy-refines-role`); `refines` names a rung (`policy-dangling-refines`); no
   chain of `refines` returns to a rung it passed (`policy-refines-cycle`); every
   chain stays in its component and ends at a base (`policy-refines-base`); no rung is
   refined twice (`policy-refines-branch`).
8. Every component has a base rung (`policy-no-base`), but a floor-only one (§7.8), which
   has no base and no refinement rung, no `source`, and at least one floor rung
   (`policy-floor-only`).
9. A rung's **layer** is 0 for a base or a floor, and one more than the rung it
   refines for a refinement; the policy has one more layer than its highest rung
   layer. No class's and no rule's `max_layer` exceeds the highest
   (`policy-class-layer`).
10. A rule's `then.ladder` names known rungs, all of one component, each once:
    exactly one base (none, for a floor-only component), every refinement over a rung it
    names (so its layers are a chain from that base), and every floor rung of the
    component (every piece has a floor, §7.1) (`policy-rule-ladder`).
11. `live.layer_lag_ms` has one entry per layer, the first 0, the entries
    non-decreasing (`policy-layer-lag`).
12. The deadline values (`defaults.deadline_ms` and every rule's `then.deadline_ms`)
    number at most 4 (`policy-too-many-deadlines`), and for every refinement layer
    *k* and every deadline value *d*, `d − layer_lag_ms[k] ≥ 1`
    (`policy-deadline-unreachable`).

Rules fold in document order: every matching rule applies, and a later `then` member
overrides an earlier one.

**3.5** A package receipt carries the policy digest. A verifier holding the effective
policy recomputes it; it cannot check that the packager followed the policy, except
by packing again.

**3.6** *What a packager may emit.* A packager **MUST** refuse a policy with a rung it
may not emit, reading SPEC §5's registry, never the policy. For each rung in ladder
order the first rule that holds is its refusal, and a policy's refusal is its first
rung's:

1. SPEC §5 does not register the capability: `capability-unknown:<cap>`.
2. SPEC §5 registers it as a record or a derivation operation, which names no payload
   format: `capability-not-payload:<cap>`.
3. It is a candidate, whose payload format no revision has pinned (SPEC §5,
   *Candidate capabilities*): `capability-candidate:<cap>`.
4. A base or a floor whose capability is not standalone media, or a refinement whose
   capability is not refinement-only: `capability-role:<cap>`.
5. Under `royalty_free_only`, a capability the registry gives no licence class:
   `license-unclassified:<cap>`; one of any class other than royalty-free:
   `license-refused:<cap>:<label>`, with the class's SPEC §5 label. The class is the
   registry's, "licensed royalty-free by its standards body"; it is not an opinion on
   freedom to operate, and a package states nothing about patents.

## 4. Pieces

**4.1** Every piece **MUST** be closed: its first frame, sample or tick is coded with
no reference outside the piece, and no later object of the package references into
it.

**4.2** Piece boundaries are a pure function of the source frames and the effective
policy; a floor-only component's, which has no source, of its first floor rung (§7.8).
Where the policy names `wai.pack.scenecut/1`, the boundaries of a component with a
source **MUST** be those §4.3 computes. The list of piece starts, in timebase units, is the **plan**, and its
digest is

    BLAKE3("wai:pack-plan\x01" ‖ u64 LE n ‖ n × u64 LE start)

**4.3** `wai.pack.scenecut/1`. All arithmetic is integer; `>>` is a shift and every
division rounds down. For each RGB8 frame *f* of `w × h` pixels:

1. Luma `Y = (77R + 150G + 29B + 128) >> 8`, and the histogram `H_f` of 64 bins,
   `Y >> 2`.
2. `D(a, b) = (Σ_i |H_a[i] − H_b[i]|) · 1000 / (2wh)`: the share of pixels, in
   thousandths, whose bin differs. The score of frame *f* ≥ 1 is `s_f = D(f, f − 1)`.
3. The current piece starts at frame *p*, and `len = f − p`. Its window `W_f` is the
   scores `s_g` for `p < g < f`, the last `cut_window` of them; `m_f` is their lower
   median (sorted ascending, the element at index `(|W_f| − 1) / 2`).
4. **Hard cut** at *f*: `len ≥ min`, `s_f ≥ cut_abs`, and either `|W_f| < 3` or
   `s_f · 1000 ≥ cut_rel · m_f`.
5. **Soft cut** at *f*: `len ≥ target` and `2 · s_f ≥ cut_abs`.
6. **Return clause.** A cut at *f* is rejected when `D(f + k, f − 1) < cut_abs` for
   some *k* in `1..=min(L, last − f)`: the content came back within *L* frames, so *f*
   starts a flash.
7. **Revisit clause.** A cut at *f* is rejected when `D(f, f − 1 − j) < cut_abs` for
   some *j* in `1..=min(L, f − 1)`: *f* returns to content seen within *L* frames, so it
   ends a flash. Frames before *p* count.
8. A hard or soft cut that clauses 6 and 7 do not reject starts a piece at *f*.
   Otherwise, when `len ≥ max`, a piece starts at *f*.

Frame 0 starts the first piece. *L* is `lookahead_frames`, *last* the index of the
source's last frame, `cut_abs` and `cut_rel` the policy's permille values, and `min`,
`target` and `max` the policy's milliseconds on the component's timebase (§4.4). A
decision about frame *f* reads no frame after `f + L`, so a live segmenter decides it
once frame `f + L` has arrived, and a live and an on-demand segmenter with equal *L*
produce equal boundaries. A piece that follows a cut is flagged a scene cut; one
started at `max`, forced.

**4.4** A piece's duration is an integer number of timebase units, and lies between
`min` and `max` except the last piece of a source, which may be shorter than `min`.
A duration in milliseconds converts to timebase units as
`floor(ms · num / (1000 · den))`; a result of 0 becomes 1, and one above `2^64 − 1`
becomes `2^64 − 1`.

A piece is at most ten minutes long (`max_ms` at most 600000) and at most `2^24` units
on its component's timebase (§3.4 item 5). A verifier takes a piece whole: it decodes
every frame of a base, holds a still's one frame for every frame of its piece and hashes
each (§5.7, §6.5), and reads one floor unit per frame (§7.2). So the longest piece a
policy allows is the most work a verifier does for one piece, and a package states it.
Ten minutes is far past any piece a delivery cuts (the default `max_ms` is four
seconds); `2^24` units bounds that work on any timebase, since a timebase may have up to
`2^32 − 1` units a second.

**4.5** *Components.* Every component of a package shares one presentation timeline
that starts at 0. The policy names one **lead** component; every other component cuts
its pieces at the lead's boundary instants, each converted to its own timebase as
`floor(start_lead · num_c · den_lead / (den_c · num_lead))` (above `2^64 − 1`,
`2^64 − 1`). A sink presents piece *p* of every component from that start.

**4.6** *Classification.* Each video piece has a kind, which rules match
(`rule.when.piece_kind`). Over the piece's consecutive frame pairs, with `Y` the luma
of §4.3:

- `mad_milli = Σ |Y_f − Y_{f−1}| · 1000 / (wh · (n − 1))`, and 0 when the piece has
  one frame (*n* = 1);
- `changed_permille` = the pixels whose luma differs, `· 1000 / (wh · (n − 1))`, and 0
  when *n* = 1;
- `occupancy` = the non-empty histogram bins of the piece's first frame.

The kind is the first that holds of: **static** (`mad_milli ≤ static_mad_milli` and
`changed_permille ≤ static_permille`); **synthetic** (`occupancy ≤ synthetic_bins`);
**motion_high** (`mad_milli ≥ motion_high_milli`); **natural**.

**4.7** *Sources.*

- **Y4M**: 8-bit 4:2:0 (`C420jpeg`, `C420paldv`, `C420mpeg2`, `C420`, or no `C`
  parameter) or 4:4:4 (`C444`), progressive. A header that is not `YUV4MPEG2` with a
  width and a height is refused `y4m-header`; an interlaced stream or frame,
  `y4m-interlaced`; another colour space, `y4m-colorspace`; a `FRAME` line that sets
  the width, height or colour space, `y4m-size-change`; a frame that ends early or a
  line that is not `FRAME`, `y4m-truncated`. Each pixel converts to RGB8 by BT.709
  limited range, with 4:2:0 chroma taken at `(y >> 1, x >> 1)`:
  - `R = clip((298(Y−16) + 459(Cr−128) + 128) >> 8)`
  - `G = clip((298(Y−16) − 55(Cb−128) − 136(Cr−128) + 128) >> 8)`
  - `B = clip((298(Y−16) + 541(Cb−128) + 128) >> 8)`

  where `>>` is the arithmetic shift and `clip` clamps to 0..=255.
- **WAV**: RIFF/WAVE with a PCM `fmt ` chunk (format tag 1) of 16-bit samples, block
  alignment `2 · channels`. Anything else is refused `wav-format`; a chunk that ends
  early, `wav-truncated`.

## 5. Objects

**5.1** *One envelope.* Each object is exactly one `WAI1` or `WAI2` envelope and
nothing after it ([http-delivery](http-delivery.md) §5.1).

**5.2** *Position independence.* An object's bytes **MUST NOT** depend on its position
in a package or on the package it belongs to: no member of its manifest names a piece,
a time, an asset, a class or a component, so two pieces with identical content are one
object. The reference packager writes a base's manifest as SPEC §3 orders it, with
`media` the component's media, `intent` `replicate`, `model_requirement` the rung's
capability with no `fallback` member, `conditioning.kind` the capability's last
dot-separated segment (`int_motion`, `av1`), and `target` `{"frames": n, "h": h, "w": w}`
(the piece's frame count and dimensions, for a still too, whose one frame is held for
the piece, §5.7; for a floor, its sequence header's maximum frame height and width); a
floor's `derived_from` (§7.2) comes after `conditioning`.

**5.3** *Name.* An object is named by its content hash ([jwp-receipts](jwp-receipts.md)
§2.1), `BLAKE3("moq-jwp:object\x01" ‖ envelope)`, as `objects/<64 lowercase hex>.wai`:
the same value is its stage-index entry (§6), its receipt leaf, its MoQ content hash and
its HTTP strong `ETag` ([http-delivery](http-delivery.md) §5.2).

**5.4** *Refinements.* A refinement object carries `refines`
([staged-delivery](staged-delivery.md) §3): `base` the content hash of its piece's base,
`layer` its layer, and as producers in `prev` only objects of the layers below it, the
object its entry refines (§6.2) among them.

The reference packager writes, for each refinement rung of a piece's ladder (§5.7), one
object of `wai.video.int_refine` over the piece's `wai.video.int_motion` base, layer by
layer. Its manifest is the one `wai stage refine` writes, as SPEC §3 orders it: `media`
the component's, `intent` `replicate`, the capability with no `fallback`,
`conditioning.kind` `wir1`, `refines` with `base` the base's content hash, `prev` the
content hash of the object of the layer below (the base for layer 1) as a string, and
`layer`, and `target` null. Its payload is a `WIR1` (staged-delivery Appendix A) of unit
kind RGB8, one unit per frame of the piece, the identity predictor and one table,
written by `wai-rs`'s refinement encoder (`staged::wir1::encode`) at the rung's step
`q`:

- each sample's residual is `rdiv(source − below, q)`, the quotient rounded half away
  from zero, where *below* is the stage the layer refines as a sink reconstructs it;
  no frame predicts another;
- the table's `offset` is the least residual and it spans every residual (where they
  span more than 4095, the 4095 around the lower median), fitted by §5.5's rule, the
  escape at 1; a residual past it is coded through the escape;
- one rANS stream per frame.

The stage the layer reconstructs, `clamp(below + r·q, 0, 255)`, is what the next layer
refines. The packer applies each layer to the decoded base with the reference sink
(staged-delivery §4) before it keeps it, and the sink's output must be the encoder's.

**5.5** *Integer video.* An object of `wai.video.int_motion` carries a `WIV1` payload
with keyframe 0, as SPEC §5 pins it ([integer-payloads](integer-payloads.md) §3); this
extension defines no other layout for it, and its decode is that section's. The
reference packager writes these with one encoder (`wai-rs` `int_video_enc`) at the step
§5.6 chooses. The encoder's choices
make a payload a function of the source frames, the rung's `block`, `search` and
`mv_precision` (§3.3), and the step `q`:

- **Motion search** (frames 1 on): blocks in raster order; for each, every vector
  `(dy, dx)` with both components in `−R..=R`, `R = search · mv_precision` (at most
  127), `dy` outer and `dx` inner, each ascending. Its cost is the sum, over the
  block's pixels inside the frame and the three channels, of `|source − prediction|`,
  where the prediction is the decode's (integer-payloads §3) from the previous frame
  as decoded. The least cost wins; a tie goes to the smaller `|dy| + |dx|`, then to the
  earlier vector.
- **Residual**: each frame, each pixel in raster order, each of R, G, B: the
  prediction (128 for frame 0) is subtracted from the source and divided by `q`,
  rounding halves away from zero; the frame as decoded is `clamp(prediction + r·q, 0,
  255)`, and the next frame predicts from it.
- **Table**: one residual table for the clip, with `offset` the least residual, `top`
  the greatest, and `h_i` the count of residual `offset + i`, for
  `n = min(top − offset + 1, 4095)` symbols. With `R = 2^16 − n − 1` and `H = Σ h_i`, symbol *i* gets frequency
  `1 + ⌊R·h_i / H⌋`; the `R − Σ⌊R·h_i / H⌋` left over go one each to the symbols with
  the largest `R·h_i mod H`, the lower symbol first on a tie; the escape gets 1. A
  residual past the table's span is coded through the bypass escape
  (integer-payloads §2).
- A clip of one frame is written with `block` 1 and `mv_precision` 1, as the format
  requires.

The encoder also states the SSE of its reconstruction against the source: the sum of
squared differences over every sample. It codes in two passes (the first finds the
vectors, the reconstruction and the residuals' counts; the second derives each
residual again and codes it last first), so beyond its input it holds the
reconstruction, the vectors, the stream and the residual table: at most
`n·h·w·3 + 24n + 12·v + 3·(2·n·h·w·3 + 16) + T` bytes for `n` frames and `v` motion
vectors (`int_video_enc::working_bytes`). `T` is the widest table's, of `S = 2·255 + 1`
symbols: its fit, `16·(S + 1) + 2·8·S + 4·(S + 2)` bytes (a frequency for each symbol
and the escape, an index for each symbol and the sort's scratch, the table), and the
table's three copies and the payload's header, `3·4·(S + 2) + 64`. For a clip past the
format's caps, which the encoder refuses before it allocates, the figure is `2^64 − 1`.

**5.6** *Choosing the step.* For each piece, the base encode of a `wai.video.int_motion`
rung chooses its step from `q_candidates`, read as a set (a value listed twice is one
candidate). It encodes the piece at each candidate, from the largest down, and chooses
the first whose `floor(SSE · 1000 / (3·w·h·n)) ≤ max_sse_px_milli`, where `SSE` is the
encoder's (§5.5) and *n* the piece's frames: the largest step that meets the bound, so
candidates that meet it alike are decided by their step. Where no candidate meets it,
it chooses the smallest. The function the reference packager's base encode calls is
`wai_pack::encode::choose_q`.

**5.7** *A piece's ladder, and stills.* A piece is coded in the rungs of its **ladder**:
those the matching rules' `then.ladder` names (§3.4 folds them: the last that sets it),
where they are rungs of the piece's component; otherwise the component's default ladder,
its first base rung in ladder order, the chain of refinement rungs over it, and its floor
rungs. A rule's ladder therefore chooses a piece's representation: its base, how many
layers refine it, and nothing else (§3.4 item 10). A piece has one entry per rung of its
ladder: its base, each refinement in layer order, then each floor (§6.2), and a
verifier holds an index to that (§11.3).

A base of `wai.image.png` is a **still**: the piece's first frame, held for the piece. A
sink presents that frame for each of the piece's frames, so its prefix is the frame
repeated and its digest the clip digest of the repeats (§6.5), its `sse` is over the
repeats against the piece's frames (§6.6), and its manifest's `target` names the piece's
frames (§5.2). The reference packager writes the frame as a PNG every byte of which is a
pure function of the frame, so an independent implementation writes the same file:

- the signature, `IHDR` (the width, the height, bit depth 8, colour type 2, compression
  0, filter 0, interlace 0), one `IDAT` holding the whole compressed stream, and `IEND`;
  each chunk a big-endian length, its type, its data and the CRC-32 of type and data;
- every row filtered `Sub` (filter byte 1): each byte less the byte three before it in
  the row, modulo 256, the first pixel's bytes less 0;
- a zlib stream (RFC 1950) of `0x78 0x01`, one final deflate block (RFC 1951) of the
  fixed Huffman codes, and the Adler-32 of the filtered rows;
- the block's symbols, from the first byte of the filtered rows: where at least three
  bytes remain and an earlier position within 32768 bytes starts with the same three
  bytes, the latest such position is the match, as long as the two runs agree (at most
  258 bytes), written as that length and the distance to it; otherwise one literal.
  Every position a symbol covers that has three bytes left becomes the latest position
  of its three bytes. The block ends with symbol 256, and the last byte is padded with
  zero bits.

A verifier reads a still as a PNG of 8-bit RGB without interlace, by PNG's chunk rules:
every chunk's type four letters and its CRC checked; `IHDR` first; an optional `PLTE`
(a suggested palette) before the image data; the `IDAT`s consecutive; ancillary chunks
read past; any other critical chunk refused; `IEND` last, empty, and nothing after it.
It inflates the zlib stream as the zlib library's inflate does, so two verifiers agree
on every stream: the header's check bits, method 8, a window of at most 32 KiB and no
preset dictionary; a stored block's length and its complement agree; at most 286
literal/length and 30 distance codes, a complete code-length code, a repeat with a
length before it and within the code lengths, and a code for the end of the block; no
Huffman code over-subscribed, and none incomplete but a literal/length or distance code
whose longest code is one bit (a lone one-bit code, or none); a code with no symbol, or
a distance past the bytes written, refused where it is read; the Adler-32, and nothing
after it. The rows are exactly `1 + 3·width` bytes each, under the five filters. A still
a verifier does not read is `prefix-digest` (§11.3).

## 6. Stage index

**6.1** A package carries, per component, one stage index, the file `index-<id>.wsix`
(`WSIX`), per window: one window for on-demand content, a chain of windows for live
(§9.2). A window holds whole pieces. Integers are little-endian.

**6.2** *Layout.* A 160-byte header, then `n_pieces` piece records of 32 bytes,
`n_entries` entry records of 128 bytes, `n_classes` class records of 16 bytes, the class
plan, and the string table. Nothing follows the string table. Reserved and padding
bytes are zero.

| Offset | Size | Header field |
|---|---|---|
| 0 | 4 | `"WSIX"` |
| 4 | 2 | version, 1 |
| 6 | 2 | `media_class`: 0 video, 1 image, 2 audio, 3 world, 4 feed, 5 avatar, 6 film |
| 8 | 4 | `tb_num` |
| 12 | 4 | `tb_den` |
| 16 | 4 | `n_pieces` |
| 20 | 4 | `n_entries` |
| 24 | 4 | `n_strings` |
| 28 | 4 | `n_classes` |
| 32 | 32 | `policy_digest` (§3.2) |
| 64 | 32 | `prev_index_digest`: the previous window's index digest; zero for on-demand content and a first window |
| 96 | 8 | `first_piece`: the absolute number of the window's first piece |
| 104 | 8 | `first_entry`: the absolute ordinal of the window's first entry across the chain |
| 112 | 32 | `plan_digest` (§4.2) of the pieces' starts |
| 144 | 2 | `component`: the component's id, as a string index |
| 146 | 14 | reserved |

| Offset | Size | Piece record field |
|---|---|---|
| 0 | 8 | `start`, in timebase units |
| 8 | 4 | `duration`, in timebase units |
| 12 | 4 | `first_entry`, window-relative |
| 16 | 2 | `n_entries` |
| 18 | 1 | `kind`: 0 natural, 1 static, 2 synthetic, 3 motion_high (§4.6), 4 world segment, 5 audio, 6 none (a floor-only component's piece, which no source classifies, §7.8) |
| 19 | 1 | flags: bit 0 scene cut, bit 1 forced at `max` (§4.3), bit 2 started by a cue, bit 3 aligned to the lead (§4.5) |
| 20 | 4 | `rules`: bit *i* set when rule *i* matched the piece (§8.1) |
| 24 | 4 | `moments`: bit *i* set when the piece lies in moment *i* (§8.1) |
| 28 | 4 | reserved |

| Offset | Size | Entry record field |
|---|---|---|
| 0 | 32 | `content_hash` (§5.3) |
| 32 | 8 | `byte_len`: the whole envelope's length |
| 40 | 8 | `piece`: the absolute piece number |
| 48 | 4 | `refines`: the window-relative index of the entry this one refines; `0xFFFFFFFF` for none |
| 52 | 2 | `capability`, as a string index |
| 54 | 1 | `role`: 0 base, 1 refinement, 2 floor, 3 snapshot, 4 ops, 5 receipt, 6 asset |
| 55 | 1 | `layer` |
| 56 | 1 | `prefix_tier`: 0 none, 1 entropy-consistency, 2 decode-equivalence (§6.4) |
| 57 | 1 | flags: bit 0 deferrable, bit 1 duplicate (an earlier entry of the index has the content hash), bit 2 the manifest carries `derived_from` |
| 58 | 2 | reserved |
| 60 | 4 | `deadline_ms`: 0 for none (§8.6) |
| 64 | 32 | `prefix_digest` (§6.5) |
| 96 | 8 | `sse` (§6.6); `2^64 − 1` when not computed |
| 104 | 4 | `manifest_len`: the envelope's `man_len` |
| 108 | 4 | reserved |
| 112 | 8 | `payload_len`: the envelope's payload bytes (for a `WAI2`, every component's) |
| 120 | 8 | reserved |

`byte_len`, `manifest_len` and `payload_len` are the envelope's own lengths; for an
object whose payload format WAI checks they are its counted bytes
([staged-measurement](staged-measurement.md) §3), so a verifier also requires each such
payload to parse as its format, after the other object rules of §6.3
(`object-lengths`).

A class record is `u16` name (a string index), `u8 max_layer`, `u8` flags (bit 0
floor only), `u32 max_kbps` (0 for none) and 8 reserved bytes, in the policy's class
order. The class plan is `n_classes` rows of `n_pieces` bytes, each the highest layer
the class lists for the piece or `0xFF` for the floor only (§8.1), zero-padded to a
multiple of 8. The string table is `n_strings` strings, each a `u16` length and that
many bytes of UTF-8, at least one, zero-padded to a multiple of 8. It is the component's
id, then the class ids in policy order, then each capability at its first use, and a
package's verifier holds an index to that (§11.3).

    index_digest = BLAKE3("wai:pack-stage-index\x01" ‖ file)
    leaf_i       = BLAKE3("wai:pack-stage\x01" ‖ entry record i)
    stage_root   = the jwp-receipts §2.2 Merkle root over the leaves

A reader **MUST** refuse a file that is not this layout, the first that applies, in
this order:

1. its first four bytes are not `WSIX`, a file of fewer included (`index-magic`);
2. a file of fewer than six bytes (`index-truncated`), or a version other than 1
   (`index-version`);
3. a file shorter than the header, or than the tables its counts give: the piece, entry
   and class records, the class plan with its padding, each string's length and bytes,
   and the string table's padding, every size taken from its count before anything is
   allocated (`index-truncated`);
4. a reserved or padding byte that is not zero (`index-reserved`);
5. a media class with no meaning (`index-media-class`); then, entry by entry, a role,
   then a tier, with none (`index-role`, `index-tier`);
6. a string that is empty or not UTF-8, then a string index past the table
   (`index-string`);
7. bytes after the string table's padding (`index-trailing`).

**6.3** *Rules.* An index lists every WAI object of its component, in piece order.
Files that are not WAI envelopes (CMAF initialization segments and fragments, FLAC
files) **MUST NOT** appear in it. A verifier **MUST** refuse an index that breaks one
of these, checked in this order:

1. A timebase of zero (`index-timebase`). An index with no previous window
   (`prev_index_digest` zero: on-demand content, or a chain's first window) whose
   `first_piece` or `first_entry` is not 0, or whose first piece does not start at 0, the
   start of the presentation timeline (§4.5) (`window-start`). Then piece by piece: a
   piece that lasts no time or does not start where the one before it ended
   (`piece-order`); whose
   `first_entry` is not the number of entries before it, or that has none
   (`piece-entries`); of a kind or with a flag that has no meaning (`piece-kind`). Then
   pieces whose entries are not the index's entries (`piece-entries`).
2. Entry by entry, in order: an entry that does not name its piece's absolute number
   (`piece-entries`); a flag with no meaning (`entry-flags`); within its piece, a role
   before one that comes earlier in the order base, refinement, floor, any other, or a
   refinement at a lower layer than the refinement before it (`entry-order`); an entry
   that is not a refinement above layer 0, a refinement at layer 0, or `refines` on an
   entry that is not a refinement or missing from one (`layer-role`); a
   refinement whose `refines` is outside the window (`refines-outside-window`), is not
   an earlier entry of its own piece (`refines-mismatch`) or is not one layer below it
   (`layer-gap`); its tier (§6.4: `tier-entropy-passthrough`, `tier-weakest`, then
   `tier-mismatch`); a non-zero `prefix_digest` with a tier other than
   decode-equivalence (`digest-without-tier`); a deadline on an entry that is not a
   refinement (`deadline-role`); a floor whose flag bit 2 is not set exactly when its
   piece has a base, so a floor presents its piece's base and a piece of floors alone
   presents none (`floor-derived-from`); a
   content hash an earlier entry has at another length (`dup-length`); the duplicate
   flag other than set exactly when an earlier entry has the content hash (`dup-flag`).
3. Class by class: a flag with no meaning (`class-flags`); a plan value other than
   `0xFF` for a floor-only class, or other than `0xFF` or at most both the class's
   `max_layer` and the piece's highest layer otherwise (`class-plan`).

With the objects in hand, a verifier **MUST** also refuse, entry by entry: bytes of
another length (`object-length`) or that do not hash to the entry's content hash
(`object-hash`); bytes that are not one `WAI1` or `WAI2` envelope and nothing else
(`non-envelope-entry`); a `man_len` or a payload length other than the entry's
(`object-lengths`); a capability other than the entry's (`object-capability`; for a
`WAI2`, its first entry's); a refinement whose object is not a `WAI1` whose `refines`
names its piece's base, its layer and producers of the layers below among which the
entry it refines (§5.4, `object-refines`); and `derived_from` (SPEC §7.1) present
otherwise than bit 2 says, or not well formed (`object-derived-from`). A member whose
value is `null` is absent; for a `WAI2`, `derived_from` is present when any entry
carries it, and well formed when every entry that carries it is. A manifest that does
not parse, or names a member twice, is not an envelope (`non-envelope-entry`).

**6.4** *Tier.* The tier a capability's own decode holds is decode-equivalence for a
capability whose registry class reconstructs exactly (`StandardDefined`, and
`NeuralIntegerExact`, whose pin a sink verifies before it decodes),
entropy-consistency for `NeuralEntropyExact`, and none otherwise (SPEC §5, §7).

- An entry at layer 0 states its capability's tier, except a floor, which states none
  (§7.4).
- A prefix with one or more refinements holds decode-equivalence only if every object
  along it does, and none otherwise ([derived-tracks](derived-tracks.md) §3, rules 1
  and 2): a refinement's tier is decode-equivalence exactly when the entry it refines
  states decode-equivalence and its own capability's tier is decode-equivalence.
- An entry with `layer` > 0 **MUST NOT** state entropy-consistency
  (`tier-entropy-passthrough`); one with `layer` > 0 that states decode-equivalence over
  a prefix that does not hold it is refused `tier-weakest`; any entry stating another
  tier than the one this section gives, `tier-mismatch`.

**6.5** `prefix_digest` is the SHA-256 decoded-output digest (SPEC §7, *Digests*) of the
prefix the entry completes when `prefix_tier` is decode-equivalence, and all zero
otherwise: for video, the clip digest over RGB8 frames (for a still, of its frame held
for the piece's frames, §5.7); for an image, the RGB8 frame digest; for audio, the digest of the s16le interleaved samples; for world, feed, avatar
and film entries, zero (their state hashes live in their receipts). A verifier decodes
the prefix and compares.

**6.6** `sse` is the integer sum, over every output sample of the prefix, of the
squared difference from the source sample the packager coded (RGB8 channels, or s16
samples). It is the producer's statement: a verifier holding the source recomputes it,
and one without the source cannot. A floor's `sse` is `2^64 − 1`.

## 7. Floor and `derived_from`

**7.1** Every piece of a video, image or audio component **MUST** have a floor rendition
in a capability of SPEC §5's mandatory floor or recommended set; a packager refuses a
video component with no floor rung (`floor-missing`). A film or world package SHOULD
have one. A component may have several floor rungs: each piece then has one floor object
per floor rung, in ladder order (§5.7), so one package carries a ladder of standard-codec
renditions over one base, which is coded once. Each floor rung has a floor name (§2): the
component's id when the component has one floor rung, the rung's id when it has several.
A floor name names files (§7.3, §7.6, §8.3), so one that cannot be one path segment of a
listing, or two floor names of a package equal once `A`–`Z` are mapped to `a`–`z`, are
refused (`pack-id`, §11.1). This revision packs supplied AV1 floors (`wai.video.av1` or
`wai.video.av1.lossless`, `source = "supplied"`), one stream per floor rung.

**7.2** *Floor objects.* Each piece's floor is one object of the floor rung's capability
(§5.2), whose manifest, except in a floor-only component (§7.8), carries `derived_from`
(SPEC §7.1, *Derived renditions*) naming the piece's base: `motif` the base's content hash, `motif_capability` its capability,
`renderer` the floor's maker, and `settings` `BLAKE3("wai:render-settings\x01" ‖
JCS(settings))` (§3.6). For a supplied floor, `renderer` is `supplied@<the supplied
listing's SHA-256>` and the settings are `{"source": "supplied", "supplied_listing":
"<that SHA-256>"}`, so neither names a position. This profile fixes these members: they
are not the producer's statement here (SPEC §7.1), and a verifier holds every floor
object to them, to its framing header and to its target (§11.3). An AV1 floor object's payload is the
length-prefixed framing the reference sink decodes (`wai-rs` `codecs::video`): `n`,
`h`, `w`, `fps_num`, `fps_den` as `u32` little-endian (the piece's temporal units, the
sequence header's maximum frame height and width, the component's timebase `num` and
`den`), then each temporal unit as a `u32` little-endian length and its bytes as the
stream holds them.

**7.3** *A supplied floor* is a directory holding, per floor rung of a video component,
`<floor name>.obu` (§7.1): an AV1 stream in the low-overhead OBU format (every OBU with
its size field), one temporal unit per source frame. Its listing (SPEC §3.1) of every
file is pinned by the policy's `floor.supplied_listing`. A packager **MUST** refuse,
before it writes anything, the directory and then each floor rung's stream in ladder
order:

- a directory whose listing does not hash to `floor.supplied_listing`
  (`floor-listing-mismatch`), and a floor rung with no stream in it
  (`floor-stream-missing`);
- a stream that does not split into temporal units each holding a frame, whose first
  unit holds no sequence header, with a sequence header whose bytes differ from the
  first's, or with a unit that starts at a shown key frame (below) without a sequence
  header (`floor-av1-malformed`);
- another number of temporal units than source frames (`floor-frame-count`);
- a unit that does not start at a shown key frame at a piece's first frame, or one that
  does elsewhere unless `floor.extra_keyframes` is true (`floor-keyframe-mismatch`). A
  unit starts at a shown key frame when its first frame header has `frame_type`
  `KEY_FRAME` and `show_frame` 1, or the sequence uses the reduced still-picture header;
  a unit that shows an existing frame does not.

*Key-frame sequence headers (informative).* A floor taken from an existing ladder without
re-encoding (its CMAF samples demuxed to this form, each with its temporal delimiter put
back) needs a sequence header in every unit that starts at a shown key frame. Where a
ladder's key-frame samples lack one, a producer that puts one back must put back the
stream's own first sequence header OBU, byte for byte, after each such unit's temporal
delimiter: §7.3 refuses any other bytes (`floor-av1-malformed`). The sequence header in
the ladder's sample entry (`av1C`) is not always the stream's: an encoder may write it
before it settles its coding tools, so that it differs from the in-band one in its tool
flags, and a stream with that header put back is refused. The packager writes its own
`av1C` from the in-band header (§7.6). A ladder whose key frames carry no in-band header
cannot be taken in the CMAF form (§7.7), whose units are its samples as they are.

The plan a supplied floor is made against is the **keyframe plan**, the file
`plan-<id>.txt`: each piece's first frame in decimal, one per line, each line ended by a
line feed. Its pieces' starts are the plan of §4.2, and `wai-pack plan` writes it from the
source and the policy before any floor is encoded.

**7.4** The floor is presentation. Its output is never compared with the primary's. A
floor object's manifest writes `intent: "replicate"`, which promises only what its
capability's decoder conformance promises (SPEC §7: `wai.video.av1` is registered
`standard-tolerance`); no tier and no claim against a primary or a source covers it.

**7.5** A floor produced by an encoder that is not a pure function of its input (§11)
**MUST** name that encoder and its version in `derived_from.renderer`, and, where the
encoder is hardware, the device and the driver that ran it.

**7.6** *CMAF.* Each floor rung's floor is also written as CMAF files, which no stage
index lists: `floor/<floor name>/init.mp4`, and one fragment per piece,
`floor/<floor name>/<SHA-256 of the fragment>.m4s`. Box layouts are ISO/IEC 14496-12's,
with the AV1 binding's sample entry; every integer is big-endian and every time 0:

- `init.mp4`: `ftyp` (major brand `cmfc`, minor version 0, compatible `cmfc`, `iso6`,
  `av01`), then `moov` holding `mvhd` (version 0, timescale `tb_num`, rate 1, volume 1,
  the unity matrix, next track 2), `trak` (`tkhd` version 0 with flags 3, track 1,
  layer, alternate group and volume 0, the unity matrix, the width and height in 16.16; `mdia`: `mdhd` version 0, timescale
  `tb_num`, language `und`; `hdlr` `vide` named `video` with its terminating zero byte;
  `minf`: `vmhd` with flags 1,
  `dinf` with one self-contained `url `, and `stbl`: `stsd` with one `av01` sample entry
  of the width and height, data reference 1, resolution 72 dpi, frame count 1, an empty
  compressor name, depth 24 and pre-defined −1, holding `av1C`, then empty `stts`,
  `stsc`, `stsz` and `stco`), and `mvex` with `trex` (track 1, sample description 1).
  `av1C` is marker and version 1, then the sequence header's profile, level, tier,
  bit depth, monochrome and chroma fields, no initial presentation delay, then the
  sequence header OBU as the stream holds it. The width and height are the sequence
  header's maximum frame width and height.
- A fragment: `moof` holding `mfhd` (sequence number piece + 1) and `traf` (`tfhd` with
  default-base-is-moof, track 1; `tfdt` version 1, the piece's start × `tb_den`; `trun`
  version 0 with data offset, sample duration, size and flags, the offset pointing at
  the `mdat` payload), then `mdat`. Each sample is a temporal unit without its temporal
  delimiter, lasting `tb_den`; its flags are `0x02000000` at a shown key frame and
  `0x01010000` otherwise.

The codecs string of the floor is the AV1 binding's short form,
`av01.<profile>.<level, two digits><M or H>.<bit depth, two digits>`.

**7.7** *A supplied CMAF floor.* With `floor.supplied_form = "cmaf"`, a supplied floor is
an existing ladder's CMAF files rather than OBU streams: per floor rung of floor name *f*
(§7.1), a directory `<f>/` holding `init.mp4` and the floor's media segments, which are
every other file of `<f>/`, each named `*.m4s` and in no directory below it, in byte order
of their names, at least one. The floor's temporal units are the segments' samples, in
order, each a temporal unit without its temporal delimiter: a unit is the two bytes
`0x12 0x00` (a temporal delimiter OBU with its size field and no extension) followed by the
sample. Boxes are ISO/IEC 14496-12's; a box's 32-bit size is at least 8, a size of 1 is the
64-bit size that follows its type (at least 16), and a size of 0 is refused; a box's
children tile its body:

- `init.mp4`: its top-level boxes tile the file; one `moov`, holding one `trak` and one
  `mvex`; the `trak`'s `tkhd` names the track, its `mdia`'s `mdhd` gives the timescale
  *T*, its `hdlr` is of handler type `vide`, and its `stsd` holds one sample entry, of type
  `av01`; an `edts`, where the `trak` has one, holds an `elst` of one entry, at media
  time 0 and rate 1; and the `mvex` holds one `trex`, of the track, whose defaults a
  sample takes.
- a media segment: its top-level boxes tile the file: boxes of the types `styp`, `sidx`,
  `prft`, `emsg`, `free` and `skip`, then one or more `moof`, each followed by an `mdat`,
  and nothing else. A `moof` holds an `mfhd` and one `traf`, and nothing else; the `traf`
  holds one `tfhd` of the track, one `tfdt` and one or more `trun`, and nothing else; the
  `tfhd`'s flags are among `0x2`, `0x8`, `0x10`, `0x20` and `0x20000` (no base data
  offset, no empty duration); each `trun`'s are among `0x1`, `0x4`, `0x100`, `0x200`,
  `0x400` and `0x800`, `0x1` (its data offset) among them. A sample's duration, size and
  flags are its `trun`'s (the first sample's flags its first-sample flags where the `trun`
  gives them), else the `tfhd`'s defaults, else the `trex`'s; its bytes start at the
  `moof`'s first byte plus its `trun`'s data offset, a run's samples one after another,
  and lie in the `mdat` after the `moof`.

A packager **MUST** refuse, before it writes anything, after the directory's listing
(§7.3), floor rung by floor rung in ladder order and segment by segment in order:

1. a floor rung with no `<f>/init.mp4` (`floor-stream-missing`); another file of `<f>/`
   that is not a media segment, or no media segment (`floor-cmaf-malformed`);
2. an `init.mp4` that is not the above (`floor-cmaf-malformed`), or whose timescale is 0
   or whose edit list is another (`floor-cmaf-timing`);
3. a media segment that is not the above, or that holds a sample of no bytes
   (`floor-cmaf-malformed`), or a sample with a composition offset other than 0 or a
   `moof` whose decode time is not where the one before it ended (`floor-cmaf-timing`),
   each where it is read; then one whose first sample is not a sync sample
   (`sample_is_non_sync_sample` set) (`floor-cmaf-malformed`); then a sample that does
   not last one frame (`duration · num = T · den`), or a segment whose first decode time
   is not the frame where the segment before it ended, the first at frame 0
   (`dts · num = frame · T · den`) (`floor-cmaf-timing`); then its units, as §7.3 reads a
   stream's (`floor-av1-malformed`, a unit's own faults held to the end);
4. then, as §7.3: a unit count other than the source's frames (`floor-frame-count`), and
   the faults held back (`floor-av1-malformed`); then an `init.mp4` whose `av01` entry has
   no `av1C`, or whose `av1C` profile, level, tier, bit depth, monochrome and chroma fields,
   or whose sample entry's width and height, are not the sequence header's and its
   maximum frame size (`floor-cmaf-malformed`): a player configures its decoder from them,
   and §8.3's playlists name the sequence header's; then a sample that is a sync sample where
   its unit does not start at a shown key frame, or that is not one where its unit does
   (`floor-cmaf-malformed`): the ladder's sample flags reach players unchanged, and
   players seek by them;
5. other than one media segment per piece of the plan, each holding exactly its piece's
   frames (`floor-cmaf-pieces`);
6. a key frame §7.3 refuses (`floor-keyframe-mismatch`).

The floor's CMAF files are then the supplied ones, byte for byte: `floor/<f>/init.mp4`
the supplied `init.mp4`, and per piece `floor/<f>/<SHA-256>.m4s` its media segment (§7.6's
writer is not used), which §8.3's playlists and MPDs list. The package also carries the
supplied floor's listing as `floor.listing`: its SHA-256 is `floor.supplied_listing`, which
the policy digest, and so the receipt, binds, and it names each of the ladder's files by
its SHA-256, so the receipt binds the ladder's bytes. A server may hold those files once,
for the ladder and the package alike (by a hard link, or by their content address): they
are the same bytes. The floor objects carry the units as §7.2 frames them, as in the OBU
form.

**7.8** *The floor-only profile.* A component of `profile = "floor-only"` is its floor
rungs alone: no base, no refinement and no source (§3.4 item 8). It is for a library that
delivers its standard-codec renditions as WAI objects, each named by its content hash,
listed in a signed stage index and bound to a signed receipt, without the integer lane.

- *Its pieces* are its first floor rung's: in the CMAF form (§7.7), one piece per media
  segment; in the OBU form (§7.3), one piece from each of the stream's shown key frames
  to the next, the stream's first unit one (`floor-keyframe-mismatch` otherwise), and the
  first floor rung's unit count is the component's frame count. A piece of more than
  `max_ms` (§4.4) is refused (`floor-piece-length`); `min_ms` and `target_ms` do not
  apply, and the scene-cut segmenter does not run. Every other floor rung is held to those
  pieces as §7.3 and §7.7 hold a floor to a plan. A piece's kind is `none` (§6.2), its
  flags 0; a rule that states `when.piece_kind` matches none of them, and its moments are
  §8.1's.
- *Its objects*: each piece has one floor object per floor rung (§7.1) and nothing else.
  A floor object presents no base, so its manifest is §5.2's for its capability with no
  `derived_from`, and its entry's flag bit 2 is clear (§6.3); everything else is §7.2's.
  Every class lists the floor only (§8.1): no catalog lists a WAI object, the MoQ catalog
  is the floors' tracks, and the package has no WAI playlist or MPD.
- *What it attests*: the receipt signs the policy, so the supplied floor's listing, and
  the stage index, so every floor object's content hash, length and capability; a
  verifier recomputes the dedup counts, holds every object to its hash and to §7.2's
  framing, its units to the AV1 stream's structure (temporal units, one per frame,
  sequence headers, shown key frames at the piece starts), and the CMAF files to the
  units (§7.6) or, in the CMAF form, to the ladder's bytes through `floor.listing`
  (§7.7). A floor-only package's catalogs list no WAI object: a sink receives the floor's
  CMAF files through HLS or DASH, or the floor's MoQ track. In the CMAF form it can check
  each segment's SHA-256 name against `floor.listing`, which the policy pins and the
  receipt signs; in the OBU form a segment's name is bound only through a verifier that
  rebuilds it from the objects (§7.6). So a sink's binding of a frame to a receipted
  object (browser-sink §7) does not apply to a floor-only package.
- *What it does not attest*: a floor states no tier (§7.4): no decoded-output digest is
  stated or checked, so nothing says what a decoder makes of the units; there is no
  source, so no `sse` and no fidelity to anything; there is no primary, so no claim
  against one, and the floor objects' `intent: "replicate"` promises their capability's
  decoder conformance and nothing more (§7.4); and the pieces are not classified. It attests delivery, not
  pictures.

## 8. Classes, catalogs and delivery

**8.1** *What a class lists.* The stages listed for a class are a pure function of the
class, the piece and the effective policy, so every viewer of a class receives the same
catalog bytes.

- A piece that starts at unit `start` and lasts `duration` units spans the
  milliseconds from `s_ms` up to `e_ms`, the floors of `start · den · 1000 / num` and of
  `(start + duration) · den · 1000 / num`; it lies in moment *i* when `s_ms < to_ms` and
  `e_ms > from_ms`. Rule *i* matches it when each condition the rule states holds: its
  kind is in `when.piece_kind`, and a tag of a moment it lies in is in
  `when.moment_tag`. Matching rules fold in document order (§3.4).
- A floor-only class lists the floor (`0xFF`), and every class lists only the floor of a
  piece with no base, a floor-only component's (§7.8). Otherwise the class lists
  `min(max_layer, the rules' then.max_layer, the piece's highest layer)`; under
  `max_kbps`, while the listed prefix needs more than `max_kbps`, that is
  `ceil(8 · bytes · num / (1000 · duration · den))` kilobits per second over the bytes of
  the listed bases and refinements, the top layer is dropped, and a base that alone
  needs more makes the piece floor-only for the class.

**8.2** A catalog **MUST NOT** list a refinement without the stages below it.

**8.3** *HTTP.* A package is offered in [http-delivery](http-delivery.md)'s Mode N
(§11.1 there): the classical presentation is the floor alone, and WAI objects are
offered in playlists of their own.

- A WAI object is none of the media segment formats of RFC 8216 §3. A WAI playlist is
  offered only to a sink that recognizes its codecs value from its own capability list,
  and a packager **MUST** write a classical master that names nothing of WAI.
- A browser's media-capabilities query answers only for the browser's own decoders,
  and **MUST NOT** be used to decide whether a `wai1.*` value can be decoded
  ([http-delivery](http-delivery.md) §4.3).
- Each class's WAI playlist **MUST** name its class and its stage view.
- A variant lists no bases without a capability in common ([http-delivery](http-delivery.md)
  §4.2, `codecs_no_common_capability`). A class's HTTP view lists a piece only where the
  piece's base is of the component's default base capability (§5.7, its first base rung's),
  and plays the floor for any other piece, as for a piece the class takes as floor only: a
  still (§5.7) among motion bases is carried over HTTP by the floor. The class's stage view
  (§8.8) and its MoQ tracks (§8.4) list it.
Durations: a piece of *d* units lasts `floor(d · den · 1000 / num)` milliseconds,
written `S.mmm` (whole seconds, a full stop, three digits). A target duration is the
largest `ceil(d · den / num)`. A rate is `ceil(8 · bytes · num / (d · den))` bits per
second; a variant's `BANDWIDTH` is the largest over the pieces it lists and
`AVERAGE-BANDWIDTH` the rate of all their bytes over all their durations. A floor
variant's bytes per piece are its fragment's; a WAI variant's are the listed bases' and
refinements', over the pieces its HTTP view lists (above). Every playlist
line ends with a line feed. For component *c*, of frame size `W×H`, and each of its
floor rungs, in ladder order, of floor name *f* (§7.1), codecs string *F* and maximum
frame size `FW×FH`:

- `hls/classic/master.m3u8`: `#EXTM3U`, `#EXT-X-VERSION:7`,
  `#EXT-X-INDEPENDENT-SEGMENTS`, then per floor rung
  `#EXT-X-STREAM-INF:BANDWIDTH=<b>,AVERAGE-BANDWIDTH=<a>,CODECS="F",RESOLUTION=FWxFH` and
  `../classic/floor-<f>.m3u8`: a URI that names the same playlist from every class's
  directory, so each class's master differs from this one only by the session-data
  line, as [http-delivery](http-delivery.md) §11.1 and §11.8 require.
- `hls/classic/floor-<f>.m3u8`, per floor rung: `#EXTM3U`, `#EXT-X-VERSION:7`,
  `#EXT-X-TARGETDURATION:<t>`, `#EXT-X-MEDIA-SEQUENCE:0`, `#EXT-X-PLAYLIST-TYPE:VOD`,
  `#EXT-X-INDEPENDENT-SEGMENTS`, `#EXT-X-MAP:URI="../../floor/<f>/init.mp4"`, then per
  piece `#EXTINF:<S.mmm>,` and `../../floor/<f>/<sha256>.m4s`, then `#EXT-X-ENDLIST`.
- `hls/<class>/master.m3u8`: the classical master, byte for byte, with, when the class
  lists a WAI object over HTTP, `#EXT-X-SESSION-DATA:DATA-ID="science.transaction.wai.multivariant",VALUE="wai.m3u8"`
  after `#EXT-X-INDEPENDENT-SEGMENTS`, and no other change.
- `hls/<class>/wai.m3u8`, when the class's HTTP view lists a WAI object: `#EXTM3U`,
  `#EXT-X-VERSION:7`, `#EXT-X-INDEPENDENT-SEGMENTS`,
  `#EXT-X-SESSION-DATA:DATA-ID="science.transaction.wai.class",VALUE="<class>"`,
  `#EXT-X-SESSION-DATA:DATA-ID="science.transaction.wai.stages",URI="../../stages/<class>.json"`,
  `#EXT-X-STREAM-INF:BANDWIDTH=<b>,AVERAGE-BANDWIDTH=<a>,CODECS="<union>",X-WAI-FLOOR="<floor>",RESOLUTION=WxH`,
  `wai-<c>.m3u8`. The union and the floor are [http-delivery](http-delivery.md) §4.2's
  over the objects the class lists.
- `hls/<class>/wai-<c>.m3u8`: the first floor rung's playlist's lines without
  `#EXT-X-MAP`, adjacent to it ([http-delivery](http-delivery.md) §11.2) and so to every
  floor rung's, which list the same pieces; per piece, `#EXT-X-GAP` when the
  class's HTTP view lists nothing of it (a floor-only piece, or one whose base is not of
  the default base capability), `#EXTINF:<S.mmm>,`, each refinement the class lists,
  in entry order, as `#WAI-LAYER:N=<layer>,URI="../../objects/<hash>.wai#n=<byte_len>"`,
  then its base as `../../objects/<hash>.wai#n=<byte_len>`: a layer line follows its
  segment's `EXTINF` ([http-delivery](http-delivery.md) §10.4).

Every HLS file above and every MPD below is a rendering of
[http-delivery](http-delivery.md)'s (Appendix G for a media playlist): the reference
packager writes them with the binding's one HLS and one DASH renderer.

DASH, the same as two MPDs ([http-delivery](http-delivery.md) §11.1), each
`<?xml version="1.0" encoding="UTF-8"?>`, then
`<MPD xmlns="urn:mpeg:dash:schema:mpd:2011" profiles="urn:mpeg:dash:profile:full:2011" type="static" mediaPresentationDuration="PT<S.mmm>S" minBufferTime="PT<t>S">`
over the component's whole duration and its target duration, `<Period id="p0" start="PT0S">`,
one `AdaptationSet`, `</Period>` and `</MPD>`, indented by two spaces a level:

- `dash/classic.mpd`: `<AdaptationSet id="1" contentType="video" mimeType="video/mp4" codecs="F" width="FW" height="FH" segmentAlignment="true" startWithSAP="1">`
  holding, per floor rung, `<Representation id="<f>-floor" bandwidth="<b>">` with
  `<SegmentList timescale="<num>">`: `<Initialization sourceURL="../floor/<f>/init.mp4"/>`,
  a `SegmentTimeline` of one `<S t="<(start − first start)·den>" d="<d·den>"/>` per
  piece, and one `<SegmentURL media="../floor/<f>/<sha256>.m4s"/>` per piece. With
  several floor rungs, the `AdaptationSet` carries no `codecs`, `width` or `height`, and
  each `Representation` carries its own after `bandwidth`:
  `<Representation id="<f>-floor" bandwidth="<b>" codecs="F" width="FW" height="FH">`.
- `dash/<class>.mpd`, when the class's HTTP view lists a WAI object:
  `<AdaptationSet id="1" contentType="video" mimeType="application/wai" codecs="<union>" width="W" height="H">`
  holding `<EssentialProperty schemeIdUri="tag:transaction.science,2026:wai/http-delivery"/>`,
  `<SupplementalProperty>`s of schemes `tag:transaction.science,2026:wai/floor` (value the
  floor), `tag:transaction.science,2026:wai/class` (the class) and
  `tag:transaction.science,2026:wai/stages` (`../stages/<class>.json`), then
  per layer *k* up to the highest the class lists, a `Representation` with attributes
  `id="<c>-l<k>"`, for *k* > 0 `dependencyId="<c>-l<k−1>"`, and `bandwidth` the peak rate of its own
  layer's objects over the pieces it lists, whose
  `SegmentList` has a timeline entry and a `SegmentURL media="../objects/<hash>.wai"`
  for each piece the class lists to layer *k* (a gap where it does not).

The media type `application/wai` is proposed, not registered
([http-delivery](http-delivery.md) §3). This revision writes the catalogs of a package
of one component; how the variants and groups of several components are written is
defined with the packing of several components.

**8.4** *MoQ.* `moq/catalog.json` is RFC 8785 canonical JSON and a line feed:
`{"tracks": [...], "version": 1}`. A component's bases and refinements are a stage set of
[moq-streaming-format](moq-streaming-format.md) §4.1, one track per (layer, deadline),
by layer, then by deadline ascending, each written as that section's entry: namespace
the policy's `asset_id`; name `<c>/l<k>`, or `<c>/l<k>@<deadline>` for a refinement
whose deadline is not `defaults.deadline_ms`; `packaging` `"wai"`; `isLive` false;
`role` `video`; `renderGroup` 1; `wai_staged` with `set` the component's id, `layer` *k*
and `lead_ms` null (an on-demand package has no live schedule); `wai_capabilities` its
entries' capabilities by first appearance (a still among them on the base track, §5.7);
`wai_determinism` the weakest tier of its entries, absent when that is none; and
receipts declared: `wai_receipts` true, `wai_receipt_alias` the first eight bytes of
`BLAKE3("wai:pack-receipt-alias\x01" ‖ namespace ‖ 0x00 ‖ name)` as a little-endian
integer, less than `2^53` (so two packages published under one key keep apart chains),
and `wai_receipts_track` `<name>/receipts`. A track `depends` on every track that
carries an entry below one of its own entries, down the chain to the base, in track
order: a track of each layer below it, none at or above it, and never one the catalog
does not hold. A sink receives every track a track depends on (moq-streaming-format
§4.1), so a dependency is all of them. A refinement track carries
`wai_delivery_timeout_ms` (§8.6), a catalog field this extension defines under the `wai_`
prefix of moq-streaming-format §4. The base track has `altGroup` 1 when the component has
a floor: each floor rung's floor, in ladder order, is a track `<f>/floor` for its floor
name *f* (§7.1), of `packaging` `"cmaf"`, in the same namespace, with `altGroup` 1,
`renderGroup` 1, `codec`, `width` and `height`, and a sink that selects a floor
subscribes to no layer track. The receipts tracks follow, one per media
track in its order, each `{"isLive": false, "name": "<name>/receipts", "namespace",
"packaging": "wai-receipts"}`. The catalog passes moq-streaming-format §4.1's check, and a
packager writes no other. A package holds no receipt: the publisher signs each track's
groups (a group a piece) on that track's chain as it publishes them (jwp-receipts §2.4.1;
§8.9 simulates it).

**8.5** *Priority.* The base track's publisher priority is 64 and layer *k*'s
`64 + 32·k`: a refinement track's value is strictly greater than that of every track it
depends on, so it is delivered after them (MOQT: a lower value is delivered first), and
moq-streaming-format §4.1's rule holds; a receipts track's is its media track's. The
priority is MOQT's (`DEFAULT_PUBLISHER_PRIORITY`), set by the publisher, not a catalog
field.

**8.6** *Deadline.* An entry's `deadline_ms` is the longest a refinement may arrive
after the base of its piece was published and still be presented; the rules' or
`defaults.deadline_ms`. A refinement track carries DELIVERY_TIMEOUT
`deadline_ms − live.layer_lag_ms[k]` (§3.4 has refused a policy where that is below 1).
Entries of one layer with different deadlines travel on different tracks. A relay may
drop a late refinement (MOQT §5.2), so a refinement never delays the base.

**8.7** *Presentation.* A sink presents piece *p* at the highest prefix whose objects
all arrived and verified by *p*'s presentation instant, and **MUST NOT** delay the base
to wait for a refinement. What the receipts of a dropped object say is
[jwp-receipts](jwp-receipts.md)' to define, not this extension's.

**8.8** *Stage views.* `stages/<class>.json` is RFC 8785 canonical JSON and a line feed:
`{"class": "<class>", "components": {"<c>": {"media_playlist":
"../hls/<class>/wai-<c>.m3u8", "pieces": [...]}}, "policy_digest": "<hex>"}`, with
`media_playlist` only when the class's HTTP view lists a WAI object (§8.3), and each piece
`{"dur", "p", "start", "stages": [...]}` with `"floor_only": true` when the class takes
it as floor only (and `stages` empty), and each listed stage `{"bytes", "h", "layer"}`,
a refinement's with `"refines"` (the content hash of the entry it refines) and
`"deadline_ms"`.

**8.9** *Delivery, simulated.* How a package's objects reach a subscriber over a link is
simulated by staged-measurement's delivery simulator ([staged-measurement](staged-measurement.md)
§10, Appendix B); its figures are labelled simulated, with their plan, and are never a
measurement of a network. The reference packager's `delivery` states the model and the
plan, and reads the outcome:

- **Model.** Each object a class lists of each piece (§8.1; a floor-only piece gives none),
  on the component's frames as units (a frame of a whole number of microseconds): base the
  piece, its layer, units the piece's frames, bytes the whole envelope, and its capture
  time the instant it is published. A live packer (§9.2) publishes a piece's base when the
  frame that decides the piece's end has arrived (the next piece's first frame plus
  `lookahead_frames`, or the source's last frame, §4.3; frame *f* arriving at
  `f · frame_us`), plus the encoder's delay, and layer *k* `layer_lag_ms[k]` after its
  base. Each refinement takes its track's delivery timeout, `deadline_ms −
  layer_lag_ms[k]` milliseconds (§8.6), as its own (staged-measurement Appendix B).
- **Plan.** Live; the link's round trip, rate and chunk; strict priority, which is §8.5's
  order; each (piece, layer) a subgroup of its own; no base timeout; the subscriber's
  layer cap (moq-streaming-format §4.1, *Capping*); one decode worker, bases first, each
  decode 1 µs (the simulation is of the link); playout from the start-up, and a refinement
  that arrives after its piece's instant discarded (§8.7).
- **Outcome.** Per piece, at its first frame's presentation instant (the start-up plus its
  start): the highest layer presented by then, or none where its base arrived later; its
  base's arrival; the layers dropped or abandoned. A class that lists nothing of any piece
  sends nothing.

Under §8.5's priorities a refinement delays a base by at most one chunk and one decode
(staged-measurement §10.4). The publisher seals each track's group with a group receipt on
the track's chain (`wai_receipt_alias`, §8.4); a subscriber accepts a delivered object by
its Merkle proof, and holds a dropped one by inclusion alone, never as delivered
([jwp-receipts](jwp-receipts.md) §4.4).

## 9. Package receipt

**9.1** A version-2 package receipt binds the asset id; the policy digest; its parent
kind and parent receipt hash; per component its id, media class, index digest and stage
root; the entry, distinct-object, referenced-byte and stored-byte counts, which a
verifier recomputes from the indexes; the packager `builtin:<crate>@<version>`; the
energy figure with its class, or the unmetered form; the grant; and the signer. Its
signing payload, big-endian:

    labelled_domain("wai:pack-receipt\x01", label)
    u32 len ‖ asset_id ‖ policy_digest[32]
    u8 parent_kind (0 none, 1 live-window, 2 re-pack) ‖ [parent_receipt_hash[32] if not 0]
    u32 n ‖ n × ( u32 len ‖ id ‖ u8 media_class ‖ index_digest[32] ‖ stage_root[32] )
    u64 total_entries ‖ u64 unique_objects ‖ u64 total_bytes ‖ u64 stored_bytes ‖ u64 work_units
    u32 len ‖ packager
    u64 joules_micro ‖ write_label(label)
    grant_hash[32] ‖ u32 len ‖ capability ‖ u64 joule_ceiling_micro ‖ u8 0 | u8 1 ‖ u64 funds_ceiling
    signer_pubkey[32] ‖ u32 len ‖ signer_id

    receipt_hash = BLAKE3("wai:video-package-receipt-id\x01" ‖ payload ‖ sig)

`labelled_domain` and `write_label` are [energy-measurement](energy-measurement.md)
§2.8's: unmetered, the domain as written and no label; metered, its final byte `\x02`
and the class's signed encoding. `total_entries` counts every entry; `unique_objects`
the distinct content hashes over every component; `total_bytes` the entries'
`byte_len`; `stored_bytes` the `byte_len` of each content hash's first entry;
`work_units` equals `total_entries`. A receipt whose content hash comes at two lengths
has no counts. The signature is Ed25519 by `signer_pubkey`, verified as SPEC §7
*Signatures* requires; a signature or a key that rule refuses is `receipt-signature`.

Its JSON form, `package.receipt.json`, is RFC 8785 canonical, hexadecimal lowercase,
integers as numbers no greater than `2^53 − 1` (a packager refuses to seal anything
else, `receipt-json`): `asset_id`; `components`, each `{"id", "index":
"index-<id>.wsix", "index_digest", "media_class", "stage_root"}`; `grant`
`{"capability", "funds_ceiling", "grant_hash", "joule_ceiling_micro"}` with `null` for
no ceiling (a joule ceiling of `2^64 − 1`); `joules_micro`; `kind` `"package"`;
`packager`; `parent_kind` (`none`, `live-window` or `re-pack`); `parent_receipt_hash`
(`null` for none); `policy_digest`; `receipt_hash`; `sig`; `signer_id`;
`signer_pubkey`; `stored_bytes`; `total_bytes`; `total_entries`; `unique_objects`;
`version` 2; `work_units`; `energy_provenance`, the class's label (energy-measurement
§2.7) or `null` when unmetered; and the class's evidence members exactly as its class
carries them. Every member is present, with `null` where it has no value
(`parent_receipt_hash`, `energy_provenance`, a grant's ceilings) and nowhere else.

A reader refuses, before anything else, JSON that is not RFC 8259 or that names a member
twice in one object, at any depth (`receipt-json`). It then reads `"version"`: absent or
1 is a version-1 receipt (§9.3), 2 a version-2 one, anything else `receipt-version`. It
then refuses (`receipt-json`) a member it does not define or one missing, `null` where
the member has a value, a value of another form (a number that is not an integer of its
range, `-0` among them; a string that is not Unicode scalar values), evidence other than
exactly what the class carries, a class label energy-measurement §2.7 refuses, a parent
kind and hash that disagree, an `index` other than `index-<id>.wsix`, and a
`receipt_hash` that is not the receipt's. A reader does not require the canonical form;
a writer writes it, and a package's `package.receipt.json` must be it (§11.3).

A verifier of a receipt against its indexes, in its components' order, refuses, the
first that applies: no component, or another number of indexes than components, a live
window's receipt included (`receipt-index-count`); an index that breaks §6 (its
reason); one that does not hash to its `index_digest` (`receipt-index-digest`), has
another stage root (`receipt-stage-root`), names another component or media class
(`receipt-component`) or another policy digest (`receipt-policy-digest`); two components
of one id (`receipt-component`); other counts, or a content hash at two lengths in any of the
indexes (`receipt-counts`); a parent kind that does not
match the indexes' `prev_index_digest`, which is zero in every index for none and a
re-pack and non-zero in every one for a live window (`receipt-parent-kind`); an energy
figure and class that do not cohere, or a legacy label (`receipt-energy`); a signature
that does not verify (`receipt-signature`).

**9.2** Live windows chain by the parent link with parent kind `live-window`. A re-pack
of an earlier package **MAY** name it with parent kind `re-pack`, and one that takes its
bases and refinements from it **MUST** (§11.5).

The reference live packer (`wai-pack live`, `wai_pack::live`) takes a source a frame at a
time, cuts it with the segmenter of §4.3, which decides a frame once `lookahead_frames`
more have arrived, and codes each piece as it closes with the coder the on-demand packer
uses (§5.4–§5.7). So a live and an on-demand pack of one source under one policy write
the same plan and the same bases and refinements, byte for byte. It writes no floor: a
supplied floor is made from the whole source (§7.3), so it is the on-demand package's.
Its pieces are gathered into windows: each a stage index of its pieces' bases and
refinements (`first_piece` and `first_entry` continuing the chain, `prev_index_digest`
the previous window's index digest, zero for the first) sealed by a version-2 receipt
whose parent is the previous window's (`live-window`; none for the first). A piece's
objects are published when the frame that decides its end has arrived: its base then,
and layer *k* `layer_lag_ms[k]` after it (§8.6, §8.9).

It writes as it goes: each object when it is published, and each window's index and
then its receipt when the window is sealed, every file whole (written beside its place
and renamed into it); the plan file and `LISTING` at the end of the source. It keeps no
record per file of the session: each file's listing line goes to a hidden file beside
the package as the file is written, and is sorted into `LISTING` at the end (the one
moment it holds a line per file); an object already written is known by its file; an
object's bytes are not held once written. What it holds is what no window has sealed
yet: those pieces' entry fields and the content hash of each object they published
first. So with windows of `n` pieces that is at most `n` pieces', and with one window
over the whole source (the default) every piece's until the end. Besides those it holds
the frames of the piece being cut and each piece's first frame, eight bytes a piece, for
the plan file. A source that fails before its end (a short frame, a frame of another
size) leaves every sealed window and the objects it lists, removes the objects only
unsealed pieces published, writes no plan file or `LISTING`, and is an error that names
what was kept.

**9.3** A version-1 receipt (`wai.video.package`'s segment map) keeps its bytes and
still verifies. Its JSON form is RFC 8785 canonical with `version` 1: `asset_id`,
`energy_provenance` (`null` when unmetered) with its evidence, `grant`, `joules_micro`,
`kind` `"package"`, `parent_receipt_hash`, `receipt_hash`, `segment_map_root`,
`segments` (each `{"byte_len", "content_hash", "duration_ms", "index"}`), `sig`,
`signer_id`, `signer_pubkey`, `stored_bytes`, `total_bytes`, `total_segments`,
`unique_segments`, `work_segment_ops`. A reader reads one without `version` as version 1,
and, because version-1 receipts were issued before this form, keeps them verifying:
`energy_provenance` may be absent (read as unmetered), an evidence member written `null`
is absent, and an on-chip counter's filtering, absent, reads as unknown. It refuses a
member named twice as version 2's reader does.
Its signing payload, big-endian, is

    "wai:video-package-receipt\x01"
    u32 len ‖ asset_id ‖ segment_map_root[32]
    u64 total_segments ‖ u64 unique_segments ‖ u64 total_bytes ‖ u64 stored_bytes ‖ u64 work_segment_ops
    u64 joules_micro ‖ class (u8 0 when unmetered, else the class's signed encoding)
    the grant as §9.1 writes it
    u8 0 | u8 1 ‖ parent_receipt_hash[32]
    u64 n ‖ n × BLAKE3("wai:video-package-seg\x01" ‖ u64 index ‖ content_hash[32] ‖ u64 duration_ms ‖ u64 byte_len)
    signer_pubkey[32] ‖ u32 len ‖ signer_id

`segment_map_root` is the jwp-receipts §2.2 Merkle root over those segment leaves, the
counts are the segments' (the bytes of one copy per content hash for `stored_bytes`), and
`receipt_hash` is version 2's.
Both versions share the identity domain, so the figure profile
`wai:video-package-receipt-id` ([energy-measurement](energy-measurement.md) §6.1)
covers both; a version-2 receipt's figure is read only with the indexes it verifies
against.

**9.4** Where the energy figure is not the unmetered form, the packager **MUST** publish
a `measurement` claim about it ([jwp-receipts](jwp-receipts.md) §2.4.8,
[energy-measurement](energy-measurement.md) §6) as
`claims/<receipt_hash>.measurement.json`: subject the receipt, figure profile
`wai:video-package-receipt-id`, signed with the package key and checked against the
receipt before it is written. A verifier refuses a metered package without it
(`measurement-claim-missing`) or with one that does not verify and check against the
receipt (`measurement-claim-invalid`). The figure brackets the whole pack: it starts once
the policy's own refusals (§3.4, §11.1) have passed, before the source's first read, and
covers both reads of the source, the supplied floor's checks (§7.3, §7.7), a parent's
verification (§11.5), every piece's coding and every file written, and stops before the
receipt is sealed. A packager **MUST NOT** leave any of that work outside it.

## 10. Royalty-free packaging

A packager run with `royalty_free_only = true` **MUST** refuse to emit any object whose
capability the registry does not classify as royalty-free, including one it does not
classify at all (§3.6, rule 5). A package receipt says nothing about patents.
`royalty_free_only` records the registry class the packager read, "licensed
royalty-free by its standards body"; it is not a freedom-to-operate opinion.

## 11. Package, re-pack equivalence and verification

**11.1** *The package* is a directory of these files and no other file or directory
(every directory below it holds one of them):

    policy.toml  policy.json  plan-<c>.txt  index-<c>.wsix  package.receipt.json
    objects/<content hash>.wai …
    floor/<f>/init.mp4  floor/<f>/<sha256>.m4s …   (per floor rung, of floor name f)
    floor.listing                                 (a supplied CMAF floor's listing, §7.7)
    hls/classic/…  hls/<class>/…  dash/…  moq/catalog.json  stages/<class>.json
    claims/<receipt_hash>.measurement.json      (a metered package)
    LISTING

`policy.toml` is the policy as given; `policy.json` its effective canonical JSON
(§3.2). `LISTING` is the listing (SPEC §3.1) of every other file, and its SHA-256 is the
**pack digest**. A component or class id or a floor name (§7.1) that cannot be one path
segment of a listing, two class ids or two floor names equal once `A`–`Z` are mapped to
`a`–`z`, and a class named `classic` in any case (ids name paths, and paths fold case)
are refused (`pack-id`).

**11.2** *Re-pack equivalence.* Given the same source bytes, effective policy, supplied
floor, signing key and packager identity, a conforming reference packager **MUST**
produce byte-identical package files on every machine and whichever fabric runs each
step (§11.6), except the energy figure and measurement claim of a metered package and
floor objects §7.5 covers. A verifier
**MAY** pack again and compare listings. A packager whose identity differs is not held
to this. A re-pack from a parent (§11.5) is held to it with the parent among its inputs;
and where the parent was packed by a conforming packager of the same identity, from the
same source, under base
and refinement rungs of the same capabilities and parameters, its files are those of a
pack that codes every piece, but for its receipt's parent and so `LISTING`.

**11.3** *Verification.* A verifier of a package, without its sources, applies these
checks in this order and refuses at the first that fails; a check that reads files a
failed check names is not applied:

1. Every file below the package's directory, read strictly — a name beginning with `.`
   and a `*.sha256` file included, as a listing (SPEC §3.1) would not skip them — is a
   regular file whose path a listing can carry; a symbolic link, a directory that
   cannot be read or holds nothing, or anything else is refused (`unexpected-file`).
2. `LISTING` is present (`listing-missing`) and is the listing of every other file
   (`listing-mismatch`).
3. `package.receipt.json` reads as a version-2 receipt (§9.1: `receipt-json`,
   `receipt-version`) and is that receipt's canonical form, byte for byte
   (`receipt-json`).
4. `policy.json` hashes to the receipt's policy digest (`policy-digest-mismatch`);
   `policy.toml` is a policy (its own reason, §3.2–§3.4); `policy.json` is its
   effective canonical JSON, `royalty_free_only` forced on where `policy.json` says
   `true` (`policy-json-mismatch`; an override never turns it off, §3.2, so a
   `policy.json` that says `false` over a `policy.toml` that says `true` is refused
   here); its ids and floor names can name files (`pack-id`, §11.1); and under that effective policy it
   asks for nothing a packager may not emit (§3.6's reason; under `royalty_free_only`, a
   patent-pool floor is `license-refused`).
5. The receipt's components are the policy's, by id, in order, each of the policy's
   media (`policy-component-mismatch`), so a package is never a receipt over fewer
   components than its policy has; each index is present (`index-missing`); the receipt
   verifies against them (§9.1, the index rules of §6 among its reasons).
6. Per component, in order:
   - the index against the policy (`index-policy-mismatch`): its timebase and media
     class are the component's; its string table is the component's id, the class ids
     in policy order, then each capability at its first use; its class records are the
     policy's classes, in order, with their `max_layer`, floor-only flag and `max_kbps`;
     every piece's kind is one a video piece has, `none` exactly in a floor-only
     component (§7.8); its rules and moments are §8.1's from
     its kind and span; its entries are the rungs of its ladder (§5.7), by role,
     capability and layer: its base, each refinement in layer order, each floor (a
     floor-only component's, its floors alone); each
     refinement's deadline is its plan's (§8.6); and its class plan is §8.1's from its
     entries;
   - the plan file holds the index's starts and its digest is the header's
     (`plan-mismatch`);
   - every entry's object is present (`object-missing`) and keeps the object rules of
     §6.3, its counted bytes included;
   - before any frame is decoded, each piece's floor objects, where the policy has floor
     rungs and an object's payload reads as §7.2's framing, hold one unit per frame of
     their piece (`floor-object-mismatch`);
   - every base and refinement, in entry order: a base decodes by its capability (a
     still is a PNG §5.7 reads, its one frame held for the piece), or it is
     `prefix-digest`; its manifest is the one §5.2 states for its piece's frames and its
     frame size (`object-manifest`); a refinement's manifest is §5.4's
     (`object-manifest`), and it applies in layer order, to every frame of the stage
     below it, by a staged-delivery §4 sink under the reference tools' cost limit and
     chain budget, or it is `prefix-digest`; a base that does not decode, or a layer that
     does not apply, ends the check;
   - then every decode-equivalent prefix decodes to its `prefix_digest`
     (`prefix-digest`);
   - when all of that holds, the floors, floor rung by floor rung in ladder order: per
     piece, one floor object per floor rung, the rung's the *k*-th floor entry for the
     *k*-th floor rung, of the rung's capability, whose renderer, settings, framing
     header, unit count and target are §7.2's (`floor-object-mismatch`) and which
     presents the piece's base (`floor-motif-mismatch`), or, in a floor-only component,
     which carries no `derived_from` (`floor-object-mismatch`); its units each one temporal unit
     holding a frame, the first of the rung's first piece carrying a sequence header,
     every sequence header the first's bytes, every shown key frame carrying one
     (`floor-av1-malformed`); each piece opening on a shown key frame, and no other unit
     being one unless the policy allows extra key frames (`floor-keyframe-mismatch`); and
     the rung's CMAF files are the ones its temporal units give (§7.6,
     `floor-cmaf-mismatch`); or, for a supplied floor in the CMAF form (§7.7), `floor.listing`
     is a listing that hashes to `floor.supplied_listing`, `floor/<f>/init.mp4` is the file
     of its line `<f>/init.mp4` and reads as §7.7's initialization segment, its `av1C` and
     sample entry size the floor's sequence header's, and the
     listing's media segments of `<f>/`, in its order, are one per piece, piece *k*'s
     `floor/<f>/<its SHA-256>.m4s`, reading as §7.7's media segment, opening on a sync
     sample, each sample one frame and the first at the piece's start, its samples the
     piece's floor units without their temporal delimiters, each a sync sample exactly
     when its unit starts at a shown key frame (`floor-cmaf-mismatch`);
   - then the catalogs are the ones the index, the objects and the floor give, and an
     index no catalog can be written for (a start past `2^53 − 1`) is refused
     (`catalog-mismatch`).
7. A metered package's measurement claim (§9.4: `measurement-claim-missing`,
   `measurement-claim-invalid`, a fabric record naming a step this extension does not
   define, §11.6, among the latter); an object file no entry names (`object-unlisted`); a
   catalog file past the ones given (`catalog-unexpected`); any other file
   (`unexpected-file`).

**11.4** *What this revision packs.* The reference packager packs one video component:
bases of `wai.video.int_motion` (§5.5, §5.6) and stills of `wai.image.png` (§5.7);
refinements of `wai.video.int_refine` over an `int_motion` base (§5.4); each piece by its
ladder, a rule's ladder subset included (§5.7); and a supplied AV1 floor per floor rung,
one or several (§7.1), in the OBU form (§7.3) or the CMAF form (§7.7); and floor-only
components (§7.8). Its live
packer packs the same pieces in windows, without a floor (§9.2). It runs `base-search`,
`sse` and `object-hash` on a GPU that qualifies, where it is built to and asked to, and
every other step on the CPU (§11.6). It refuses by name,
before writing anything, what it does not pack yet: another medium
(`pack-media-unsupported`), a floor to encode (`pack-floor-encode-unsupported`), and a rung
of a capability it does not encode, or a refinement over a base it does not refine
(`pack-capability-unsupported:<cap>`, every one naming the capability of the rung it does
not pack); and a component of the standard profile with no source (`pack-source-missing`;
a floor-only component has none, §7.8) or whose source's frame rate is not its timebase
(`pack-source-rate`). Where its own work fails it
refuses by name too, and leaves nothing written (a file it wrote before the refusal is
removed): an encode the encoder refuses, such as a piece
past the samples it holds, or an object it wrote that does not count (`pack-encode`); a
piece past `2^32 − 1` units (`pack-piece-length`); catalogs it cannot write, the case
§11.3 refuses as `catalog-mismatch` (`pack-catalog`); a meter that was asked for and
gives no figure, a span too short to reach a microjoule or a figure past `2^64 − 1`
(`pack-meter`, never an unmetered package in its place); a measurement claim it cannot
write (`pack-measurement-claim`); a listing it cannot write (`pack-listing`); and a source
that does not read the same twice (`pack-source-changed`) or a supplied floor stream that
does not (`floor-listing-mismatch`): it reads each a frame or a temporal unit at a time,
once to cut and check it and once to code it, and holds neither whole. What it holds is
not a function of the source's length but for a record per piece and per entry and a byte
per frame of each floor (whether it starts at a key frame): the frames of the pieces it
codes at once, which it chooses, each piece coded alone (§4.1), so the package is the same
for any number; one piece of each floor; and, for the catalogs, one object at a time,
read back from where it wrote it; except a re-pack, which holds its parent whole while it
verifies it (§11.5), so its memory grows with the parent. Each file is written whole as it
is made. It
writes a package only into a directory that is new or holds nothing, and refuses any
other before it packs (`pack-out-not-empty`): written among another package's files, it
would leave behind the ones it does not write.

**11.5** *Re-pack from a parent.* A packager **MAY** take every piece's base and
refinements from an earlier package, its **parent**, instead of coding them, so a
component's integer base is coded once and taken by every package made from the same
source after it. It reads the source as for a pack that codes (§4: its pieces and their
kinds, §4.3, §4.6, are this source's), and **MUST** refuse, checks 1 and 2 before it
writes anything and check 3 as it reads each piece, leaving nothing written (§11.4):

1. a parent that does not verify as §11.3 verifies a package (`repack-parent-invalid`,
   with the reason the parent fails for);
2. a parent with no component of the component's id, media and timebase, or whose pieces
   are not this source's, piece by piece: another number of pieces, or a piece of
   another start, duration, flags or kind, or whose ladder (§5.7, under the parent's
   policy) codes its base and refinements in rungs of other capabilities or other
   parameters (§3.3) than this policy's ladder for the piece, in layer order, or with
   another deadline (§8.6) (`repack-parent-mismatch`);
3. a piece whose prefixes, each the parent's base decoded and its refinements applied in
   layer order by a staged-delivery §4 sink, do not reconstruct this source with the
   `sse` the parent's entry states (§6.6) (`repack-source-mismatch`): a parent packed
   from another source.

It then writes, for each piece, the parent's base and refinement objects and their
entries' fields (§6.2: content hash, lengths, capability, role, layer, tier, prefix
digest, `sse`, deadline) in place of coding them, and the floors as it would; its
receipt names the parent's receipt with parent kind `re-pack` (§9.1). A verifier holding
the parent **MAY** check a re-pack against it: the parent verifies
(`repack-parent-invalid`), the re-pack's receipt names the parent's receipt with parent
kind `re-pack`, and each component's pieces are the parent's, piece by piece, of the same
start, duration, kind and flags, whose base and refinement entries are the parent's
entries, every field the same but the entry's place in its index: the entry it refines
counted from its piece's first entry, and the duplicate flag, which an index's own
entries decide (`repack-parent-mismatch`). A re-pack holds no source of its parent's
bases; what binds a reused base to this source is the third check, and what binds it to
the parent is the receipt.

**11.6** *Steps and fabrics.* The steps of a pack and a verify are named by these terms:

| Step | What it computes |
|---|---|
| `source-decode` | a source's frames from a coded rendition, before a pack, by a producer's tool (§4.7 reads the result) |
| `source-read` | a source's frames or samples (§4.7) |
| `segment` | the pieces (§4.3) and their kinds (§4.6) |
| `base-search` | the integer base's motion search (§5.5) |
| `base-code` | the rest of the integer base (§5.5), its step (§5.6) and a still (§5.7) |
| `refine-code` | refinement layers, each applied by the reference sink (§5.4) |
| `sse` | an entry's `sse` (§6.6) |
| `object-hash` | an object's content hash (§5.3) |
| `digest` | the SHA-256 digests: decoded-output digests (§6.5), listings, file names |
| `floor-read` | a supplied floor's units, CMAF boxes and listing (§7.3, §7.7) |
| `floor-decode` | a floor's units decoded to pictures (item 4 below) |
| `index` | the stage indexes, catalogs, receipt and claim (§6, §8, §9) |
| `io` | reading and writing files |

Every step is a function of its inputs, defined in integers (and `floor-decode` by the
AV1 decoding process), and none names a fabric:

1. *Packages.* A packager **MAY** run a step on any fabric whose output is the step's
   for every input. It **MUST NOT** run a step on a backend that has not, on each device
   it opens and before it is used, given the step's output for every input of a
   qualifying set, nor at all on one that computes otherwise than the step's
   definition, such as in floating
   point where the step is defined in integers, or with a learned approximation. A
   backend that cannot take a call (a size, a lost device) leaves it to the CPU, with the
   same output. So §11.2 holds across fabrics: the package files are the same bytes
   whichever fabric ran each step, and only a metered package's measurement claim says
   where they ran. A qualifying set holds, at the least:
   - for the motion search (§5.5), frame pairs of noise, of a smooth field, of a flat
     field (every candidate ties in cost) and of alternating columns (two vectors tie
     in cost and in length), at sizes that are not a whole number of blocks, at three
     block sizes or more, at full-pel and half-pel precision, and with search ranges
     that reach the frame's edge;
   - for SSE, inputs of at least three lengths, among them one byte and one past
     4096 bytes;
   - for BLAKE3, messages of 0 and 1 bytes, of 1023, 1024 and 1025 bytes around a chunk,
     and longer than four chunks.
   (Informative: the reference packager's set is `wai_pack::fabric::qualifying_frames`
   and the inputs of `wai_pack::fabric::qualify`.)
2. *Verdicts.* A verifier's verdict and its reason are functions of the package
   (§11.3). A verifier **MAY** compute a check on another fabric where the package states
   the value the check compares with, such as an object's content hash: a match shows
   that the fabric computed the check, and a mismatch **MUST** be computed again on the
   reference implementation before it is reported. Every other check runs on a backend
   held to the reference's output as item 1 holds a packager's. A verdict that changes
   with the fabric is the verifier's fault, never the package's.
3. *Hardware encoders.* A hardware encoder's output depends on the chip, its firmware
   and driver, and its settings, and no rule fixes it, so no step of this extension is
   computed by one. A floor a packager is given is an input, whatever made it (§7.3,
   §7.7); a floor a packager encodes on such hardware is one §7.5 covers, whose
   `derived_from.renderer` names what §7.5 requires, and §11.2 does not hold its bytes.
4. *Decoding a floor.* The AV1 decoding process fixes every output sample of a stream
   whose sequence header has `film_grain_params_present` 0, and of every stream before
   film grain is applied (AV1 §7.2), so conformant decoders on any fabric give the same
   pictures of a floor's units. A floor states no decoded-output digest (§7.4), so a
   decode of it has no stated value to compare with: a verifier that decodes floors
   **MUST NOT** refuse a package for what a decoder other than the reference gives, nor
   read a hardware decoder's error or concealment as a verdict. A hardware decoder's
   frames may be held in a wider format than the stream's bit depth (a 10-bit sample
   shifted into the high bits of a 16-bit word); a reader of them recovers each sample
   exactly or refuses the frame, and never rounds. (Informative: `wai-pack floor-decode`
   reports each piece's digest from either decoder, for comparing them.)
5. *The fabric record.* A metered package's measurement claim **MAY** carry a fabric
   record (jwp-receipts §2.4.8, energy-measurement §6.3): each step the metered span ran,
   with every fabric that ran it and its backend, and the figure's share on each. Its
   steps are this section's terms (§11.3 step 7). An unmetered package carries no claim,
   so no record: which fabric ran a step is not part of the package, and two packages
   that differ only in where their steps ran are the same files.

## 12. Reasons

| Reason | Where |
|---|---|
| `policy-toml` (not UTF-8, a byte-order mark, not TOML 1.0, nesting past 32), `policy-float`, `policy-datetime`, `policy-negative`, `policy-integer-range` | §3.2 |
| `policy-unknown-key`, `policy-missing-key`, `policy-type`, `policy-value`, `policy-schema` | §3.3 |
| `policy-too-many-components`, `policy-too-many-rungs`, `policy-too-many-classes`, `policy-too-many-rules`, `policy-too-many-moments`, `policy-duplicate-id`, `policy-lead`, `policy-open-gop`, `policy-piece-bounds`, `policy-ladder-component`, `policy-refines-role`, `policy-dangling-refines`, `policy-refines-cycle`, `policy-refines-base`, `policy-refines-branch`, `policy-no-base`, `policy-floor-only`, `policy-class-layer`, `policy-rule-ladder`, `policy-layer-lag`, `policy-too-many-deadlines`, `policy-deadline-unreachable` | §3.4 |
| `capability-unknown`, `capability-not-payload`, `capability-candidate`, `capability-role`, `license-unclassified`, `license-refused`, each naming the capability (and the licence label) | §3.6 |
| `y4m-header`, `y4m-interlaced`, `y4m-colorspace`, `y4m-size-change`, `y4m-truncated`, `wav-format`, `wav-truncated` | §4.7 |
| `index-magic`, `index-version`, `index-truncated`, `index-reserved`, `index-media-class`, `index-role`, `index-tier`, `index-string`, `index-trailing` | §6.2 |
| `index-timebase`, `window-start`, `piece-order`, `piece-entries`, `piece-kind`, `entry-flags`, `entry-order`, `layer-role`, `refines-outside-window`, `refines-mismatch`, `layer-gap`, `tier-entropy-passthrough`, `tier-weakest`, `tier-mismatch`, `digest-without-tier`, `deadline-role`, `floor-derived-from`, `dup-length`, `dup-flag`, `class-plan`, `class-flags` | §6.3, §6.4 |
| `object-length`, `object-hash`, `non-envelope-entry`, `object-lengths`, `object-capability`, `object-refines`, `object-derived-from` | §6.3 |
| `floor-missing`, `floor-listing-mismatch`, `floor-stream-missing`, `floor-av1-malformed`, `floor-frame-count`, `floor-keyframe-mismatch` | §7.1, §7.3 |
| `floor-stream-missing`, `floor-cmaf-malformed`, `floor-cmaf-timing`, `floor-cmaf-pieces` | §7.7 |
| `floor-keyframe-mismatch`, `floor-piece-length` | §7.8 |
| `floor-object-mismatch`, `floor-motif-mismatch`, `floor-av1-malformed`, `floor-keyframe-mismatch`, `floor-cmaf-mismatch`, against a package | §11.3 |
| `receipt-json`, `receipt-version`, `receipt-index-count`, `receipt-index-digest`, `receipt-stage-root`, `receipt-component`, `receipt-policy-digest`, `receipt-counts`, `receipt-parent-kind`, `receipt-energy`, `receipt-signature` | §9.1 |
| `measurement-claim-missing`, `measurement-claim-invalid` | §9.4 |
| `unexpected-file`, `listing-missing`, `listing-mismatch`, `policy-digest-mismatch`, `policy-json-mismatch`, `policy-component-mismatch`, `index-missing`, `index-policy-mismatch`, `plan-mismatch`, `object-missing`, `object-manifest`, `prefix-digest`, `catalog-mismatch`, `catalog-unexpected`, `object-unlisted` | §11.3 |
| `pack-id`, `pack-source-missing`, `pack-source-rate`, `pack-media-unsupported`, `pack-floor-encode-unsupported`, `pack-capability-unsupported` (naming the capability) | §11.1, §11.4 |
| `pack-encode`, `pack-piece-length`, `pack-catalog`, `pack-meter`, `pack-measurement-claim`, `pack-listing`, `pack-source-changed`, `pack-out-not-empty` | §11.4 |
| `repack-parent-invalid`, `repack-parent-mismatch`, `repack-source-mismatch` | §11.5 |