Crate oxideav_av1 

oxideav-av1

Status: orphan-rebuild scaffold (post 2026-05-20 audit), clean room rebuild in progress.

The decoder/encoder pipeline is not wired up yet. Bitstream parsing has reached:

• Round 1. OBU bytestream walker described in §5.3 of the AV1 Bitstream & Decoding Process Specification — boundaries in a low-overhead bitstream plus obu_type / obu_extension_flag / obu_has_size_field / temporal_id / spatial_id / obu_size fields and a payload slice for each unit. See [obu].

• Round 2. Sequence header OBU parse per §5.5 (sequence_header_obu, color_config, timing_info, decoder_model_info, operating_parameters_info). Returns a strongly typed [sequence_header::SequenceHeader] descriptor plus a bit-position so the trailing-bits accounting from §5.3.1 can plug in cleanly next round. See [sequence_header].

• Round 3. Leading slice of uncompressed_header() per §5.9.2 — show_existing_frame / frame_to_show_map_idx / display_frame_id / frame_type / show_frame / showable_frame / error_resilient_mode / disable_cdf_update / allow_screen_content_tools / force_integer_mv / current_frame_id / frame_size_override_flag / order_hint / primary_ref_frame / refresh_frame_flags. Composes with round-2’s SequenceHeader to drive every conditional read. See [frame_header].

• Round 4. Frame-size sub-syntax block per §5.9.5 (frame_size) + §5.9.6 (render_size) + §5.9.8 (superres_params) + §5.9.9 (compute_image_size). For every intra (KEY_FRAME / INTRA_ONLY_FRAME) frame in the §5.9.2 syntax tree, [parse_frame_header] now drops into frame_size() + render_size() after refresh_frame_flags and surfaces the eight-field [FrameSize] descriptor (frame_width / frame_height / render_width / render_height / superres_denom / upscaled_width / mi_cols / mi_rows). The §5.9.7 frame_size_with_refs() found_ref shortcut is not implemented yet — it reads RefUpscaledWidth[] / RefFrameHeight[] / RefRenderWidth[] / RefRenderHeight[] from a reference-frame state table this round does not track — so inter-frame parsing still stops at refresh_frame_flags with frame_size = None. See [frame_header].

• Round 6. allow_intrabc (§5.9.3 path of §5.9.2) + tile_info() (§5.9.15) wired into the streaming [parse_frame_header] walk. For intra frames whose allow_screen_content_tools && UpscaledWidth == FrameWidth conjunction holds, the parser now consumes the allow_intrabc f(1) slot — otherwise the spec’s allow_intrabc = 0 initialiser stands. After the frame_size() / render_size() block (intra path), the parser then walks tile_info() per §5.9.15 and surfaces a typed [tile_info::TileInfo] (uniform_tile_spacing_flag, tile_cols, tile_rows, tile_cols_log2, tile_rows_log2, context_update_tile_id, tile_size_bytes, mi_col_starts, mi_row_starts). The non-uniform-spacing path consumes the ns(maxWidth) / ns(maxHeight) width_in_sbs_minus_1 / height_in_sbs_minus_1 fields via the new [bitreader::BitReader::ns] primitive (§4.10.7). Tile-content decode (motion vectors, transform / quantisation, in-loop filters, film grain) is still out of scope. See [tile_info].

• Round 5. Uncompressed-header tail sub-syntaxes — §5.9.10 read_interpolation_filter() (returns [InterpolationFilter]), §5.9.11 loop_filter_params() (returns [LoopFilterParams] with the CodedLossless || allow_intrabc short-circuit, the four loop_filter_level[] fields with the NumPlanes > 1 && (level[0] || level[1]) gate on the chroma slots, the f(3) loop_filter_sharpness, and the loop_filter_delta_enabled / delta_update / update_ref_delta[i] / update_mode_delta[i] per-slot update walk over TOTAL_REFS_PER_FRAME = 8 ref-deltas + 2 mode-deltas with su(7) signed offsets), and §5.9.12 quantization_params() + §5.9.13 read_delta_q() (returns [QuantizationParams] with base_q_idx, the four delta_q_y_dc / delta_q_u_dc / delta_q_u_ac / delta_q_v_dc / delta_q_v_ac per-plane offsets, diff_uv_delta / using_qmatrix / qm_y / qm_u / qm_v). These remain available as standalone parser entry points ([parse_interpolation_filter], [parse_loop_filter_params], [parse_quantization_params]) for callers that want to exercise the parsers on a raw byte slice. See [uncompressed_header_tail].

• Round 7. §5.9.12 quantization_params() and §5.9.14 segmentation_params() wired into the streaming [parse_frame_header] walk (intra path). After tile_info() the parser now consumes quantization_params() and surfaces a typed [QuantizationParams] on [FrameHeader::quantization_params], then segmentation_params() and surfaces a typed [SegmentationParams] on [FrameHeader::segmentation_params] covering segmentation_enabled, segmentation_update_map, segmentation_temporal_update, segmentation_update_data, the full §5.9.14 FeatureEnabled[i][j] / FeatureData[i][j] 8×8 table (segment_feature_active / segment_feature_data), and the §5.9.14 trailing SegIdPreSkip / LastActiveSegId derivations. The §5.9.14 primary_ref_frame == PRIMARY_REF_NONE collapse is honoured (update_map = 1, temporal_update = 0, update_data = 1, no bitstream reads for the three update flags). Per-feature Segmentation_Feature_Bits / Segmentation_Feature_Signed / Segmentation_Feature_Max Table 5.9.14 tables are exposed as [SEGMENTATION_FEATURE_BITS] / [SEGMENTATION_FEATURE_SIGNED] / [SEGMENTATION_FEATURE_MAX]. See [uncompressed_header_tail::parse_segmentation_params].

• Round 8. §5.9.17 delta_q_params() and §5.9.18 delta_lf_params() wired into the streaming [parse_frame_header] walk (intra path). After segmentation_params() the parser consumes delta_q_params() and surfaces a typed [DeltaQParams] on [FrameHeader::delta_q_params] (delta_q_present — read as f(1) only when base_q_idx > 0; delta_q_res — f(2), read only when delta_q_present == 1), then delta_lf_params() and surfaces a typed [DeltaLfParams] on [FrameHeader::delta_lf_params] (delta_lf_present — gated on delta_q_present and suppressed when allow_intrabc == 1; delta_lf_res / delta_lf_multi — read only when delta_lf_present == 1). Both remain available as standalone parser entry points ([uncompressed_header_tail::parse_delta_q_params] / [uncompressed_header_tail::parse_delta_lf_params]).

• Round 9 — §5.9.11 loop_filter_params() wired into the streaming [parse_frame_header] walk (intra path). After delta_lf_params() the parser derives CodedLossless from the §5.9.2 lines that scan LosslessArray[] over the per-segment qindexes (get_qindex(1, segmentId) with the §8.7 ignore-delta branch and the SEG_LVL_ALT_Q Clip3(0, 255, ..) clamp), then consumes loop_filter_params() and surfaces a typed [LoopFilterParams] on [FrameHeader::loop_filter_params]. The §5.9.11 CodedLossless || allow_intrabc short-circuit consumes no bits and resets the ref-deltas to their §5.9.11 defaults; the full path reads the four loop_filter_level[] slots (chroma pair gated on NumPlanes > 1 && (level[0] || level[1])), the f(3) loop_filter_sharpness, and the loop_filter_delta_enabled / delta_update per-slot update walk.

• Round 10 — §5.9.19 cdef_params() wired into the streaming [parse_frame_header] walk (intra path). After loop_filter_params() the parser consumes cdef_params() and surfaces a typed [CdefParams] on [FrameHeader::cdef_params]. The §5.9.19 CodedLossless || allow_intrabc || !enable_cdef short-circuit consumes no bits and leaves cdef_bits = 0, CdefDamping = 3, and all four strength arrays zeroed; the full path reads cdef_damping_minus_3 / cdef_bits and the 1 << cdef_bits cdef_y_pri / cdef_y_sec (+ cdef_uv_* when NumPlanes > 1) strength entries, applying the secondary == 3 ⇒ += 1 adjustment. Also available as a standalone parser entry point ([parse_cdef_params]).

• Round 11 — §5.9.20 lr_params() wired into the streaming [parse_frame_header] walk (intra path). After cdef_params() the parser consumes lr_params() and surfaces a typed [LrParams] on [FrameHeader::lr_params]. The §5.9.20 AllLossless || allow_intrabc || !enable_restoration short-circuit consumes no bits and leaves every plane RESTORE_NONE with UsesLr = 0; the full path reads one lr_type (f(2)) per plane (mapped through Remap_Lr_Type into [FrameRestorationType]), then — when any plane uses LR — lr_unit_shift (post-incremented for 128×128 superblocks, otherwise extended by lr_unit_extra_shift) and the 4:2:0-chroma-gated lr_uv_shift, deriving the three LoopRestorationSize[] entries from RESTORATION_TILESIZE_MAX. Also available as a standalone parser entry point ([parse_lr_params]).

• Round 12 — §5.9.21 read_tx_mode() wired into the streaming [parse_frame_header] walk (intra path). After lr_params() the parser consumes read_tx_mode() and surfaces a typed [TxMode] on [FrameHeader::tx_mode]. When CodedLossless == 1 the §5.9.21 first branch consumes no bits and forces [TxMode::Only4x4]; otherwise the f(1) tx_mode_select slot selects [TxMode::TxModeSelect] (1) or [TxMode::TxModeLargest] (0). Also available as a standalone parser entry point ([parse_tx_mode]).

• Round 13 — the §5.9.2 uncompressed-header tail completes the intra path. After read_tx_mode() the parser consumes frame_reference_mode() (§5.9.23), skip_mode_params() (§5.9.22), the allow_warped_motion slot, reduced_tx_set (f(1)), global_motion_params() (§5.9.24), and film_grain_params() (§5.9.30), surfacing [FrameHeader::reference_select] / skip_mode_present / allow_warped_motion / reduced_tx_set plus typed [GlobalMotionParams] and [FilmGrainParams]. For an intra frame the first three blocks and global_motion_params() all collapse without reading bits (the §5.9.23 FrameIsIntra ⇒ reference_select = 0, the §5.9.22 skipModeAllowed = 0, the §5.9.2 allow_warped_motion guard, and the §5.9.24 FrameIsIntra identity short-circuit); reduced_tx_set is one bit, and film_grain_params() reads its full §5.9.30 block when the sequence enables grain and the frame carries apply_grain == 1. global_motion_params() exposes the complete §5.9.24/§5.9.25 inter syntax (read_global_param + §5.9.26–§5.9.29 decode_signed_subexp_with_ref / decode_subexp / inverse_recenter) via the standalone [parse_global_motion_params]; film_grain_params() is likewise available via [parse_film_grain_params] (taking a [FilmGrainContext]). This is the end of uncompressed_header() for the intra path — [FrameHeader::bits_consumed] now reaches the trailing bits / tile-group boundary.

• Round 14 — the inter-frame uncompressed_header() path. An INTER_FRAME / SWITCH_FRAME header now parses end-to-end. The §5.9.2 else branch reads frame_refs_short_signaling, the explicit ref_frame_idx[] (or computes them via §7.8 set_frame_refs()), the §5.9.7 frame_size_with_refs() / §5.9.5 frame_size() + §5.9.6 render_size() size selection, allow_high_precision_mv, §5.9.10 read_interpolation_filter(), is_motion_mode_switchable, use_ref_frame_mvs, then the shared disable_frame_end_update_cdf + tile_info() + quant / segment / delta / loop-filter / CDEF / LR / read_tx_mode() tail, the inter frame_reference_mode() (reference_select), §5.9.22 skip_mode_params(), allow_warped_motion, reduced_tx_set, inter global_motion_params(), and film_grain_params(). Backed by a new public [frame_header::RefInfo] cross-frame reference state and surfaced via [parse_frame_header_with_refs] / [frame_header::InterFrameRefs] (on [FrameHeader::inter_refs]). Verified byte-exact against the i-frame-then-p-64x64 fixture’s idx=1 FRAME_HEADER + REF_MAP trace lines.

• Round 15. The §8.2 symbol (arithmetic / msac) decoder, as a standalone [symbol_decoder::SymbolDecoder]. Implements §8.2.2 init_symbol (the SymbolValue / SymbolRange / SymbolMaxBits §8.2.4 state), §8.2.6 read_symbol (the CDF-adaptive multisymbol search with EC_PROB_SHIFT / EC_MIN_PROB, the prev - cur range update, and the seven-step renormalisation that draws new bits — or §8.2.2 padding zeros once SymbolMaxBits is exhausted), the §8.3 adaptive-rate CDF update, §8.2.3 read_bool, §8.2.5 read_literal (L(n)), NS(n) (§4.10.10), the arithmetic-coded decode_subexp_bool (§5.9.28 bool variant), and §8.2.4 exit_symbol (trailing-bit accounting + byte-alignment advance, rejecting the SymbolMaxBits < -14 conformance violation via Error::SymbolExitUnderflow). The default CDF tables (§9.4) and the §8.3.2 CDF-selection process are out of scope this round — they land with the tile-content decode that consumes them. See [symbol_decoder].

• Round 16. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 CDF-selection process for a bounded intra-frame mode / partition syntax group, in a new [cdf] module. Transcribes [DEFAULT_INTRA_FRAME_Y_MODE_CDF] (the intra_frame_y_mode 5×5×14 table), the five DEFAULT_PARTITION_W{8,16,32,64,128}_CDF tables (the partition element), [DEFAULT_SKIP_CDF], and [DEFAULT_SEGMENT_ID_CDF] verbatim from §9.4. [TileCdfContext] implements §8.3.1 (new_from_defaults copies every Default_* table into a per-tile, mutable Tile*Cdf working set that the §8.2 [SymbolDecoder] adapts in place), and the §8.3.2 selection surfaces a &mut [u16] row for each element — intra_frame_y_mode ([abovemode][leftmode]), partition (array-by-bsl, row-by-ctx), skip ([ctx]), and segment_id ([ctx]) — feeding [SymbolDecoder::read_symbol] directly. The scalar §8.3.2 context-derivation helpers ([intra_mode_ctx] / [partition_ctx] / [skip_ctx] / [segment_id_ctx]) compute the index from neighbour inputs the (future) tile walk supplies. The remaining ~100 §9.4 tables, the init_coeff_cdfs coefficient set, and the other §8.3.2 selections (split_or_horz / split_or_vert / tx_depth / txfm_split / the motion-vector + uv-mode groups) are a clear followup. See [cdf].

• Round 17. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 CDF-selection process for the motion-vector component syntax group, extending [cdf]. Transcribes [DEFAULT_MV_JOINT_CDF], [DEFAULT_MV_SIGN_CDF], [DEFAULT_MV_CLASS_CDF], [DEFAULT_MV_CLASS0_BIT_CDF], [DEFAULT_MV_CLASS0_FR_CDF], [DEFAULT_MV_CLASS0_HP_CDF], [DEFAULT_MV_BIT_CDF], [DEFAULT_MV_FR_CDF], and [DEFAULT_MV_HP_CDF] verbatim from §9.4 (the 216*128 / 136*128 / … fixed-point notation expanded). [TileCdfContext] grows nine mv_* working-set fields broadcast per §8.3.1 to MV_CONTEXTS = 2 slots (and to the comp = 0..1 axis where the source default is per-comp identical), and the §8.3.2 selection surfaces &mut [u16] rows for every MV element: mv_joint ([MvCtx]), mv_sign / mv_class / mv_class0_bit / mv_class0_hp / mv_fr / mv_hp ([MvCtx][comp]), mv_class0_fr ([MvCtx][comp][mv_class0_bit]), and mv_bit ([MvCtx][comp][i]). The §5.11.31 MvCtx derivation — MvCtx = use_intrabc ? MV_INTRABC_CONTEXT : 0 — is exposed as the [mv_ctx] helper. The remaining ~90 §9.4 tables (y_mode, uv_mode, angle-delta, tx-size, coefficient, palette, …) and the other §8.3.2 selections are a mechanical followup against the same [TileCdfContext] shape.

• Round 18. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 selection for the inter-mode / reference-frame syntax group, extending [cdf]. Transcribes the 13 remaining Default_*_Cdf tables driving every inter-block mode and reference syntax: [DEFAULT_NEW_MV_CDF], [DEFAULT_ZERO_MV_CDF], [DEFAULT_REF_MV_CDF], [DEFAULT_DRL_MODE_CDF], [DEFAULT_IS_INTER_CDF], [DEFAULT_COMP_MODE_CDF], [DEFAULT_SKIP_MODE_CDF], [DEFAULT_COMP_REF_CDF], [DEFAULT_COMP_BWD_REF_CDF], [DEFAULT_SINGLE_REF_CDF], [DEFAULT_COMPOUND_MODE_CDF], [DEFAULT_COMP_REF_TYPE_CDF], [DEFAULT_UNI_COMP_REF_CDF] verbatim from §9.4, plus the §8.3.2 [COMPOUND_MODE_CTX_MAP] lookup table. [TileCdfContext] grows the corresponding Tile*Cdf fields, [TileCdfContext::new_from_defaults] seeds them per §8.3.1, and the §8.3.2 selection surfaces &mut [u16] rows for every element: new_mv_cdf / zero_mv_cdf / ref_mv_cdf / drl_mode_cdf / is_inter_cdf / comp_mode_cdf / skip_mode_cdf / comp_ref_cdf / comp_bwd_ref_cdf / single_ref_cdf / compound_mode_cdf / comp_ref_type_cdf / uni_comp_ref_cdf. Scalar §8.3.2 context helpers [is_inter_ctx] (the (AvailU, AvailL) × (AboveIntra, LeftIntra) branch ladder), [skip_mode_ctx] (neighbour SkipModes[] sum), [ref_count_ctx] (< / == / > three-branch shared by every single_ref_p* / comp_ref / comp_bwdref / uni_comp_ref_p* paragraph), and [compound_mode_ctx] (Compound_Mode_Ctx_Map lookup) compute each ctx from the neighbour-summary inputs the (future) tile walk supplies.

• Round 20. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 selection for the transform-size syntax group, extending [cdf]. Transcribes the four per-maxTxDepth tx_depth tables ([DEFAULT_TX_8X8_CDF], [DEFAULT_TX_16X16_CDF], [DEFAULT_TX_32X32_CDF], [DEFAULT_TX_64X64_CDF]) and the binary [DEFAULT_TXFM_SPLIT_CDF] verbatim from §9.4. [TileCdfContext] grows the tx_8x8 / tx_16x16 / tx_32x32 / tx_64x64 / txfm_split fields, all seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces two &mut [u16] accessors — tx_depth_cdf(maxTxDepth, ctx) (the §8.3.2 four-way TileTx{8x8,16x16,32x32,64x64}Cdf[ ctx ] switch keyed by Max_Tx_Depth[ MiSize ]; returns None when maxTxDepth == 0) and txfm_split_cdf(ctx). Scalar §8.3.2 context helpers [tx_depth_ctx] (the (aboveW >= maxTxWidth) + (leftH >= maxTxHeight) formula) and [txfm_split_ctx] (the (txSzSqrUp != maxTxSz) * 3 + (TX_SIZES - 1 - maxTxSz) * 6 + above + left formula) compute each ctx from scalar inputs the §5.11.15 / §5.11.16 syntax supplies.

• Round 21. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 selection for the inter-frame transform-type syntax group, extending [cdf]. Transcribes the three Default_Inter_Tx_Type_Set{1,2,3}_Cdf tables ([DEFAULT_INTER_TX_TYPE_SET1_CDF], [DEFAULT_INTER_TX_TYPE_SET2_CDF], [DEFAULT_INTER_TX_TYPE_SET3_CDF]) verbatim from §9.4 — Set1 for the full 16-symbol set (4x4 / 8x8 inter blocks), Set2 for the 16x16 inter set (12 symbols), Set3 for the reduced 2-symbol { IDTX, DCT_DCT } set (4x4..32x32 inter blocks). [TileCdfContext] grows the inter_tx_type_set1 / inter_tx_type_set2 / inter_tx_type_set3 fields, all seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces an &mut [u16] accessor inter_tx_type_cdf(set, tx_size_sqr) (the §8.3.2 three-way TX_SET_INTER_{1,2,3} switch; returns None for TX_SET_DCTONLY per §5.11.47 and for any unreachable (set, tx_size_sqr) combination). The scalar §5.11.48 helper [inter_tx_type_set] computes the set ∈ { TX_SET_DCTONLY, TX_SET_INTER_1, TX_SET_INTER_2, TX_SET_INTER_3 } from the (Tx_Size_Sqr[txSz], Tx_Size_Sqr_Up[txSz], reduced_tx_set) tuple supplied by the surrounding §5.11.47 syntax. The intra counterpart (Default_Intra_Tx_Type_Set{1,2}_Cdf with their extra intraDir axis) and the remaining §9.4 tables (y_mode, uv_mode, angle-delta, coefficient, …) are mechanical followups against the same [TileCdfContext] shape.

• Round 22. The §9.4 default CDF table and the §8.3.1 / §8.3.2 selection for the inter-frame interpolation-filter syntax element, extending [cdf]. Transcribes [DEFAULT_INTERP_FILTER_CDF] — [INTERP_FILTER_CONTEXTS][INTERP_FILTERS + 1], i.e. 16 contexts × 3 cumulative frequencies + adaptation counter — verbatim from §9.4. New §3 constants INTERP_FILTERS = 3 and INTERP_FILTER_CONTEXTS = 16. [TileCdfContext] grows the interp_filter field, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces interp_filter_cdf(ctx); the scalar [interp_filter_ctx] helper folds the §8.3.2 four-branch (above_type, left_type, dir, is_compound) formula into a single 0..INTERP_FILTER_CONTEXTS index (the caller supplies the already-resolved neighbour-type values per the spec’s RefFrame[0] matching predicate). Sentinel [INTERP_FILTER_NONE] (== INTERP_FILTERS, mirroring the spec’s literal 3) marks an unavailable / mismatched neighbour.

• Round 23. The §9.4 default CDF table and the §8.3.1 / §8.3.2 selection for the motion-mode syntax element, extending [cdf]. Transcribes [DEFAULT_MOTION_MODE_CDF] — [BLOCK_SIZES][MOTION_MODES + 1], i.e. 22 block-size rows × 3 cumulative frequencies + adaptation counter — verbatim from §9.4. New §3 constant MOTION_MODES = 3 (per §6.10.26 SIMPLE = 0 / OBMC = 1 / LOCALWARP = 2). [TileCdfContext] grows the motion_mode field, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces motion_mode_cdf(mi_size) — a straight 0..BLOCK_SIZES index (the spec’s selection text reads “TileMotionModeCdf[ MiSize ]”; no neighbour-context arithmetic).

• Round 24. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 selection for the compound-prediction syntax elements, extending [cdf]. Transcribes [DEFAULT_COMP_GROUP_IDX_CDF] ([COMP_GROUP_IDX_CONTEXTS][3]), [DEFAULT_COMPOUND_IDX_CDF] ([COMPOUND_IDX_CONTEXTS][3]) and [DEFAULT_COMPOUND_TYPE_CDF] ([BLOCK_SIZES][COMPOUND_TYPES + 1]) verbatim from §9.4. New §3 constants COMPOUND_TYPES = 2, COMP_GROUP_IDX_CONTEXTS = 6, COMPOUND_IDX_CONTEXTS = 6. [TileCdfContext] grows the comp_group_idx / compound_idx / compound_type fields, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces comp_group_idx_cdf(ctx) / compound_idx_cdf(ctx) (binary, precomputed-ctx index) and compound_type_cdf(mi_size) (a straight 0..BLOCK_SIZES index; the spec’s selection text reads “TileCompoundTypeCdf[ MiSize ]”).

• Round 134. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 selection for the inter-frame intra-mode syntax elements, extending [cdf]. Transcribes [DEFAULT_Y_MODE_CDF] ([BLOCK_SIZE_GROUPS][INTRA_MODES + 1]), [DEFAULT_UV_MODE_CFL_NOT_ALLOWED_CDF] ([INTRA_MODES][UV_INTRA_MODES_CFL_NOT_ALLOWED + 1]) and [DEFAULT_UV_MODE_CFL_ALLOWED_CDF] ([INTRA_MODES][UV_INTRA_MODES_CFL_ALLOWED + 1]) verbatim from §9.4. New §3 constants BLOCK_SIZE_GROUPS = 4, UV_INTRA_MODES_CFL_NOT_ALLOWED = 13, UV_INTRA_MODES_CFL_ALLOWED = 14 plus the §8.3.2 [SIZE_GROUP] table. [TileCdfContext] grows the y_mode / uv_mode_cfl_not_allowed / uv_mode_cfl_allowed fields, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces y_mode_cdf(ctx) (with [size_group] performing the ctx = Size_Group[ MiSize ] mapping) and uv_mode_cdf(cfl_allowed, y_mode) (picking the cfl-allowed / cfl-not-allowed variant by the resolved flag, then indexing by YMode).

• Round 135. The §9.4 default CDF table and the §8.3.1 / §8.3.2 selection for the angle-delta syntax elements (angle_delta_y / angle_delta_uv), extending [cdf]. Transcribes [DEFAULT_ANGLE_DELTA_CDF] ([DIRECTIONAL_MODES][(2 * MAX_ANGLE_DELTA + 1) + 1]) verbatim from §9.4. New §3 constants DIRECTIONAL_MODES = 8, MAX_ANGLE_DELTA = 3 and the directional-mode base V_PRED = 1. [TileCdfContext] grows the angle_delta field, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces angle_delta_cdf(mode), which rebases a directional YMode / UVMode onto 0..DIRECTIONAL_MODES via mode - V_PRED (the TileAngleDeltaCdf[ YMode - V_PRED ] / TileAngleDeltaCdf[ UVMode - V_PRED ] selection).

• Round 136. The §9.4 default CDF tables and the §8.3.1 init_coeff_cdfs / §8.3.2 selection for the coefficient-token entry sub-group — the gateway to tile-content decode: the transform-block skip flag ([DEFAULT_TXB_SKIP_CDF]), the end-of-block position class ([DEFAULT_EOB_PT_16_CDF] … [DEFAULT_EOB_PT_1024_CDF]), the EOB extra-bit ([DEFAULT_EOB_EXTRA_CDF]), and the DC sign ([DEFAULT_DC_SIGN_CDF]), all transcribed verbatim from §9.4. New §3 constants PLANE_TYPES = 2, COEFF_CDF_Q_CTXS = 4, TXB_SKIP_CONTEXTS = 13, EOB_COEF_CONTEXTS = 9, DC_SIGN_CONTEXTS = 3. Unlike the non-coeff CDFs, these are reset by the separate [TileCdfContext::init_coeff_cdfs] (base_q_idx → idx via [coeff_cdf_q_ctx]) so the working copy drops the COEFF_CDF_Q_CTXS axis, selecting Default_*_Cdf[ idx ]. The coeff_base / coeff_base_eob / coeff_br braid is deferred to a later round.

• Round 137. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 selection for the intra-frame transform-type syntax group, completing the §6.10.19 transform-set coverage started in round 21. Transcribes [DEFAULT_INTRA_TX_TYPE_SET1_CDF] ([INTRA_TX_TYPE_SET1_SIZES][INTRA_MODES][TX_TYPES_INTRA_SET1 + 1], i.e. [2][13][8] per the §9.4 listing) and [DEFAULT_INTRA_TX_TYPE_SET2_CDF] ([INTRA_TX_TYPE_SET2_SIZES][INTRA_MODES][TX_TYPES_INTRA_SET2 + 1], i.e. [3][13][6]) verbatim from §9.4 — Set1 for the full 7-symbol intra set (4x4 / 8x8 intra blocks), Set2 for the reduced 5-symbol set (4x4 / 8x8 / 16x16 intra blocks). Both tables carry an extra intraDir axis (INTRA_MODES = 13) on top of the Tx_Size_Sqr axis already seen in the inter counterparts. New §3 constants TX_SET_INTRA_1 = 1, TX_SET_INTRA_2 = 2, TX_TYPES_INTRA_SET1 = 7, TX_TYPES_INTRA_SET2 = 5, INTRA_TX_TYPE_SET1_SIZES = 2, INTRA_TX_TYPE_SET2_SIZES = 3, and the §8.3.2 [FILTER_INTRA_MODE_TO_INTRA_DIR] table. [TileCdfContext] grows the intra_tx_type_set1 / intra_tx_type_set2 fields, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces an &mut [u16] accessor intra_tx_type_cdf(set, tx_size_sqr, intra_dir) (the §8.3.2 two-way TX_SET_INTRA_{1,2} switch over the §8.3.2 intraDir axis; returns None for TX_SET_DCTONLY per §5.11.47 and for any unreachable (set, tx_size_sqr, intra_dir) combination). The scalar §5.11.48 helper [intra_tx_type_set] computes the set ∈ { TX_SET_DCTONLY, TX_SET_INTRA_1, TX_SET_INTRA_2 } from the (Tx_Size_Sqr[txSz], Tx_Size_Sqr_Up[txSz], reduced_tx_set) tuple supplied by the surrounding §5.11.47 syntax (the intra branch differs from the inter one in two places: txSzSqrUp == TX_32X32 itself routes to TX_SET_DCTONLY rather than TX_SET_INTER_3, and the txSzSqr == TX_16X16 branch routes to TX_SET_INTRA_2 rather than TX_SET_INTER_2). The scalar §8.3.2 helper [intra_dir] derives the intraDir axis from the use_filter_intra flag plus the YMode / filter_intra_mode pair.

• Round 138. The §9.4 default CDF table and the §8.3.1 init_coeff_cdfs / §8.3.2 selection for the first member of the coeff_base / coeff_base_eob / coeff_br braid: [DEFAULT_COEFF_BASE_EOB_CDF] ([COEFF_CDF_Q_CTXS][TX_SIZES][PLANE_TYPES][SIG_COEF_CONTEXTS_EOB][4]), transcribed verbatim from §9.4. coeff_base_eob codes the base level of the last non-zero coefficient (the base level is coeff_base_eob + 1; only 1, 2, or 3 are coded). New §3 constant SIG_COEF_CONTEXTS_EOB = 4. [TileCdfContext] grows the coeff_base_eob field, seeded by [TileCdfContext::new_from_defaults] from the idx == 0 slice and re-selected per base_q_idx by [TileCdfContext::init_coeff_cdfs]. The §8.3.2 selection surfaces coeff_base_eob_cdf(tx_sz_ctx, ptype, ctx), the three-way TileCoeffBaseEobCdf[ txSzCtx ][ ptype ][ ctx ] lookup; the §8.3.2 ctx derivation (get_coeff_base_ctx() - SIG_COEF_CONTEXTS + SIG_COEF_CONTEXTS_EOB) belongs to the not-yet-implemented tile-content walk and is deferred. The remaining two tables of the braid (Default_Coeff_Base_Cdf and Default_Coeff_Br_Cdf) are deferred to later rounds.

• Round 139. The §9.4 default CDF table and the §8.3.1 init_coeff_cdfs / §8.3.2 selection for the second member of the coeff_base / coeff_base_eob / coeff_br braid: [DEFAULT_COEFF_BASE_CDF] ([COEFF_CDF_Q_CTXS][TX_SIZES][PLANE_TYPES][SIG_COEF_CONTEXTS][5], 1680 5-entry rows; declared static so clippy::large_const_arrays does not flag the per-use copy hazard), transcribed verbatim from §9.4. coeff_base codes the base level of each non-EOB coefficient — a 4-symbol alphabet (0..3). New §3 constant SIG_COEF_CONTEXTS = 42. [TileCdfContext] grows the coeff_base field, seeded by [TileCdfContext::new_from_defaults] from the idx == 0 slice and re-selected per base_q_idx by [TileCdfContext::init_coeff_cdfs]. The §8.3.2 selection surfaces coeff_base_cdf(tx_sz_ctx, ptype, ctx), the three-way TileCoeffBaseCdf[ txSzCtx ][ ptype ][ ctx ] lookup; the get_coeff_base_ctx() derivation itself belongs to the not-yet-implemented tile-content walk and is deferred. The largest (TX_SIZE = TX_64X64, ptype = chroma) slice is a flat {8192, 16384, 24576, 32768, 0} placeholder across every q-context and ctx value (an unreachable-chroma sentinel mirroring the r138 (tx4, pt1) placeholder pattern). The last remaining table of the braid (Default_Coeff_Br_Cdf) is deferred to a later round.

• Round 140. The §9.4 default CDF table and the §8.3.1 init_coeff_cdfs / §8.3.2 selection for the LAST member of the coeff_base / coeff_base_eob / coeff_br braid: [DEFAULT_COEFF_BR_CDF] ([COEFF_CDF_Q_CTXS][TX_SIZES][PLANE_TYPES][LEVEL_CONTEXTS][BR_CDF_SIZE + 1], 840 5-entry rows; declared static so clippy::large_const_arrays does not flag the per-use copy hazard), transcribed verbatim from §9.4. With this table all three coefficient-CDF braid members are landed. coeff_br codes the per-coefficient base-range increment used to push a level above NUM_BASE_LEVELS: each read codes a value in 0..BR_CDF_SIZE = 4, and §5.11.39 stacks COEFF_BASE_RANGE / (BR_CDF_SIZE - 1) such reads per coefficient. New §3 constants LEVEL_CONTEXTS = 21 and BR_CDF_SIZE = 4. [TileCdfContext] grows the coeff_br field, seeded by [TileCdfContext::new_from_defaults] from the idx == 0 slice and re-selected per base_q_idx by [TileCdfContext::init_coeff_cdfs]. The §8.3.2 selection surfaces coeff_br_cdf(tx_sz_ctx, ptype, ctx), implementing the spec selector TileCoeffBrCdf[ Min(txSzCtx, TX_32X32) ][ ptype ][ ctx ] with the TX_32X32 = 3 clamp built in (so any txSzCtx is accepted; only ptype / ctx are bounds-checked); the get_br_ctx() derivation itself belongs to the not-yet-implemented tile-content walk and is deferred. The largest (TX_SIZE = TX_64X64, ptype = chroma) slice is again a flat {8192, 16384, 24576, 32768, 0} placeholder, mirroring the r138 / r139 pattern. The next gate is the §8.3.2 get_coeff_base_ctx() / get_br_ctx() neighbour-derivation helpers (deferred to a different round — they need tile-content walker state).

• Round 141. The §8.3.2 neighbour-derivation helpers that close out the coefficient-CDF braid: [get_coeff_base_ctx] and [get_br_ctx] (plus the [get_coeff_base_eob_ctx] wrapper that subtracts SIG_COEF_CONTEXTS and adds SIG_COEF_CONTEXTS_EOB to land on the EOB-CDF context range). Each consumes a coefficient-magnitude array Quant[] (laid out row-major with stride Tx_Width[ adjTxSz ]) plus the position-in-scan + tx-class + tx-size and returns the ctx index consumed by the matching coeff_base_eob_cdf / coeff_base_cdf / coeff_br_cdf selector. [get_tx_class] performs the §8.3.2 TxType -> TxClass reduction (V_DCT / V_ADST / V_FLIPADST -> [TX_CLASS_VERT], H_DCT / H_ADST / H_FLIPADST -> [TX_CLASS_HORIZ], everything else -> [TX_CLASS_2D]). New §3 constants [TX_SIZES_ALL] (= 19), [SIG_COEF_CONTEXTS_2D] (= 26), [SIG_REF_DIFF_OFFSET_NUM] (= 5), [NUM_BASE_LEVELS] (= 2), [COEFF_BASE_RANGE] (= 12), [TX_CLASS_2D], [TX_CLASS_HORIZ], [TX_CLASS_VERT]. New §-Additional- tables transcriptions [TX_WIDTH], [TX_HEIGHT], [TX_WIDTH_LOG2], [ADJUSTED_TX_SIZE], [SIG_REF_DIFF_OFFSET], [MAG_REF_OFFSET_WITH_TX_CLASS], [COEFF_BASE_CTX_OFFSET], [COEFF_BASE_POS_CTX_OFFSET]. Caller still owns the tile-content walk that supplies Quant[] itself plus the compute_tx_type() derivation that feeds [get_tx_class]; this round delivers the per-coefficient ctx plumbing those callers will consume.

• Round 142. The §5.11.40 compute_tx_type() derivation — [compute_tx_type], the per-plane / per-block transform-type lookup the tile-content walker reads before kicking off coefficient decoding. Implements the full spec function: Lossless || Tx_Size_Sqr_Up[ txSz ] > TX_32X32 short-circuits to DCT_DCT; plane == 0 returns the TxTypes[ blockY ][ blockX ] luma cache entry; is_inter chroma reads the cache at (Max(MiRow, blockY << subsampling_y), Max(MiCol, blockX << subsampling_x)) then runs the [is_tx_type_in_set] admission filter; intra chroma reads [MODE_TO_TXFM][UVMode] then runs the same filter. The §5.11.40 is_tx_type_in_set(txSet, txType) predicate is a direct read of [TX_TYPE_IN_SET_INTER] / [TX_TYPE_IN_SET_INTRA]. The caller supplies the §5.11.40 txSet (i.e. the already-resolved [inter_tx_type_set] / [intra_tx_type_set] result) and a closure over TxTypes[y][x] so the helper does not bake in a particular storage shape. New §6.10.16 ordinal constants [TX_4X4] / [TX_8X8] / [TX_16X16] / [TX_32X32] / [TX_64X64] replace the local const TX_* shadows the existing [inter_tx_type_set] / [intra_tx_type_set] helpers used. New §6.10.19 transform-type ordinals [DCT_DCT] through [H_FLIPADST] (16 entries) name the previously-numeric entries. New §-Additional-tables transcription [TX_SIZE_SQR_UP] (Tx_Size_Sqr_Up[ TX_SIZES_ALL ], t -> Max(w, h)-sided square). New §5.11.40 tables [MODE_TO_TXFM] (chroma-mode -> default transform-type), [TX_TYPE_IN_SET_INTRA] (TX_SET_TYPES_INTRA = 3 rows of TX_TYPES = 16 admission flags), [TX_TYPE_IN_SET_INTER] (TX_SET_TYPES_INTER = 4 rows). The derivation is pure / msac- independent — the tile walker plugs it in once MiRow / MiCol / subsampling_x / subsampling_y / UVMode / TxTypes state lands. 278 -> 288 tests, zero #[ignore].

• Round 143. The §9.4 default CDF tables and the §8.3.1 / §8.3.2 selection for the inter-intra syntax group (interintra, interintra_mode, wedge_interintra — the §5.11.28 read_interintra_mode triple). Transcribes [DEFAULT_INTER_INTRA_CDF] ([BLOCK_SIZE_GROUPS - 1][3]), [DEFAULT_INTER_INTRA_MODE_CDF] ([BLOCK_SIZE_GROUPS - 1][INTERINTRA_MODES + 1]) and [DEFAULT_WEDGE_INTER_INTRA_CDF] ([BLOCK_SIZES][3]) verbatim from §9.4. New §3 constant [INTERINTRA_MODES] (= 4, per §6.10.27 II_DC_PRED / II_V_PRED / II_H_PRED / II_SMOOTH_PRED). [TileCdfContext] grows the inter_intra / inter_intra_mode / wedge_inter_intra fields, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection surfaces inter_intra_cdf(ctx) / inter_intra_mode_cdf(ctx) (the scalar [interintra_ctx] helper folds the spec’s ctx = Size_Group[ MiSize ] - 1 into a single 0..(BLOCK_SIZE_GROUPS - 1) index, returning None for the Size_Group[ MiSize ] == 0 rows that the §5.11.28 syntax gate excludes) and wedge_inter_intra_cdf(mi_size) (a straight 0..BLOCK_SIZES index). The wedge table’s outer dimension is transcribed full-width per the §9.4 listing; per its note only indices 3..=9 (the BLOCK_8X8..BLOCK_32X32 band) are reachable. 288 -> 296 tests, zero #[ignore].

• Round 144. The §9.4 default CDF table and the §8.3.1 / §8.3.2 selection for the wedge-index syntax element — wedge_index, read by both §5.11.28 read_interintra_mode (the inter-intra wedge sub-branch, when wedge_interintra == 1) and §5.11.29 read_compound_type (the inter-inter COMPOUND_WEDGE branch). Transcribes [DEFAULT_WEDGE_INDEX_CDF] ([BLOCK_SIZES][WEDGE_TYPES + 1]) verbatim from §9.4 (p.435). New §3 constant [WEDGE_TYPES] (= 16, the spec text reads “Number of directions for the wedge mask process”). [TileCdfContext] grows the wedge_index field, seeded by [TileCdfContext::new_from_defaults] per §8.3.1. The §8.3.2 selection wedge_index_cdf(mi_size) is a straight TileWedgeIndexCdf[ MiSize ] index. The table’s outer dimension is transcribed full-width per the §9.4 listing; per its note (p.436) indices 0..2, 10..17, and 20..21 are never used in the first dimension (matching the §3 Wedge_Bits[ MiSize ] == 0 rows) and carry the placeholder uniform CDF { 2048, 4096, …, 30720, 32768, 0 } (step 32768 / WEDGE_TYPES). 296 -> 302 tests, zero #[ignore].

• Round 145. The §8.3.2 split_or_horz / split_or_vert cdf-derivation helpers — [split_or_horz_cdf] and [split_or_vert_cdf] — that build a 2-symbol binary cdf out of the already-selected partition cdf (the spec’s partitionCdf) per p.362. Each helper folds the §9.4 partition probabilities of the “splittable plus orthogonal-axis” symbols into a single psum, then emits cdf[0] = (1 << 15) - psum, cdf[1] = 1 << 15, cdf[2] = 0; per the §8.3.2 note the probability of the disallowed orthogonal partition gets folded into the split probability, so split_or_horz cannot return a PARTITION_VERT and split_or_vert cannot return a PARTITION_HORZ. The b_size != BLOCK_128X128 guard drops the PARTITION_*_4 term that the §9.4 Default_Partition_W128_Cdf row has no entry for. New §6.10.4 / §3 ordinal constants [PARTITION_NONE] / [PARTITION_HORZ] / [PARTITION_VERT] / [PARTITION_SPLIT] / [PARTITION_HORZ_A] / [PARTITION_HORZ_B] / [PARTITION_VERT_A] / [PARTITION_VERT_B] / [PARTITION_HORZ_4] / [PARTITION_VERT_4] + [EXT_PARTITION_TYPES] (= 10) + the block-size ordinal [BLOCK_128X128] (= 15) replace the literal indices the §8.3.2 formulas use. 302 -> 312 tests, zero #[ignore].

• Round 146. The §5.11.50 get_palette_color_context derivation — the function the §5.11.49 diagonal walk reads at each palette_color_idx_* position to produce the ColorOrder[ PALETTE_COLORS ] permutation + ColorContextHash that flow back through [palette_color_ctx] into the §8.3.2 cdf selector. Surface: [palette_color_context_from_neighbors] (pure-scoring core taking the three optional neighbour palette indices) and [get_palette_color_context] (spec-faithful 2-D entry that applies the §5.11.50 r > 0 / c > 0 boundary guards). The [PaletteColorContext] struct packages both outputs. The partial selection sort is the §5.11.50 three-iteration loop that promotes the top-scoring neighbours to the head of ColorOrder while preserving the runners-up’s ascending order; the hash is the Palette_Color_Hash_Multipliers- weighted sum of the top three sorted scores. 312 -> 323 tests, zero #[ignore].

• Round 147. The §5.11.49 palette_tokens( ) per-plane diagonal walker — the §5.11.49 caller-facing entry point that drives the §5.11.50 colour-context derivation across one of the planes’ anti-diagonal walk, decodes one palette_color_idx_{y,uv} per (i - j, j) against the cdf row picked by [palette_color_ctx], remaps through ColorOrder[idx], and fills the on-screen border by replicating the last on-screen column / row. Surface: [palette_tokens_plane] (driving the [SymbolDecoder] + [TileCdfContext]) and the [PalettePlane] selector. Two new Error variants surface caller-bug preconditions (Error::InvalidPaletteWalkArgs) and the §5.11.50 unreachable hash slots (Error::PaletteColorContextUnmapped). 323 -> 334 tests, zero #[ignore].

• Round 148. The §9.3 block-size conversion tables (av1-spec p.400–401) — four BLOCK_SIZES-indexed lookup tables that turn a MiSize into block dimensions: [MI_WIDTH_LOG2], [MI_HEIGHT_LOG2], [NUM_4X4_BLOCKS_WIDE], [NUM_4X4_BLOCKS_HIGH], plus the §3 constants [MI_SIZE] (4) and [MI_SIZE_LOG2] (2). Surface: the four tables plus the six MiSize-keyed const fn accessors [block_width], [block_height], [num_4x4_blocks_wide], [num_4x4_blocks_high], [mi_width_log2], [mi_height_log2]. The Block_Width[ x ] = 4 * Num_4x4_Blocks_Wide[ x ] spec identity is encoded as the NUM_4X4_BLOCKS_WIDE[ x ] << MI_SIZE_LOG2 shift so the identity is not duplicated as a numeric table. These feed the §5.11.49 [palette_tokens_plane] caller staged in r147 and unblock the wider §5.x reconstruction call sites that the parser will surface once read_block is wired. 334 -> 344 tests, zero #[ignore].

• Round 149. The §5.11.49 caller-side argument derivation (av1-spec p.101-102) — [palette_tokens_args] computes the four [PaletteTokensArgs] dimensions (blockWidth, blockHeight, onscreenWidth, onscreenHeight) from the parser-scope (MiSize, MiRow, MiCol, MiRows, MiCols, plane, subsampling_x, subsampling_y) tuple. Reuses the §9.3 tables staged in r148 and the §5.11.46 palette gate constant [BLOCK_8X8] (3). Both spec branches handled: the Y branch returns the §9.3-driven dimensions clipped by Min(.., (MiRows - MiRow) * MI_SIZE) / Min(.., (MiCols - MiCol) * MI_SIZE), the UV branch applies the >> subsampling_{x,y} shift then the §5.11.49 <4-bump (block_w += 2; onscreen_w += 2 when post-shift block_w < 4, ditto for height). Walker invariants (1 <= onscreen_* <= block_*, block_* <= 64) proven over every palette-eligible (MiSize, sub_x, sub_y, plane) combination. Bridges the data-flow gap pinned by the r147 follow-up test so read_block can call palette_tokens once the parser surfaces it. 344 -> 359 tests, zero #[ignore].

• Round 150. The §9.3 Partition_Subsize[ 10 ][ BLOCK_SIZES ] lookup (av1-spec p.402-403) plus the §3 enumeration of the 22 named BLOCK_* ordinals and the [BLOCK_INVALID] (22) sentinel. [PARTITION_SUBSIZE] transcribes the table verbatim — every rectangular bSize column carries BLOCK_INVALID per the av1-spec p.401 note “The table will never get accessed for rectangular block sizes”. The typed accessor [partition_subsize] folds the sentinel into Option<usize> (None on BLOCK_INVALID or out-of-range indices) so the upcoming §5.11.4 decode_partition() body can read subSize = Partition_Subsize[ partition ][ bSize ] / splitSize = Partition_Subsize[ PARTITION_SPLIT ][ bSize ] and never hand a sentinel to its recursive children. Tests cover row-3 (SPLIT) halving identity, row-1 (HORZ) / row-2 (VERT) halving, row-4..7 (_A / _B) row equality with rows 1 / 2, row-8..9 (_4) quarter-splits, the BLOCK_4X4-only-resolves-for-PARTITION_NONE column-0 invariant, exhaustive rectangular-bSize-is-invalid coverage, and the §5.11.4 subdivision-shrinks-area invariant. The 22 BLOCK_* constants and BLOCK_INVALID are also pinned against their av1-spec p.171-172 / p.7 ordinals. 359 -> 375 tests, zero #[ignore].

• Round 151. The §5.11.4 decode_partition( r, c, bSize ) body (av1-spec p.61-62) — the recursive partition-tree walker that stitches r137-r145’s §9.4 partition-default CDFs, r145’s §8.3.2 [split_or_horz_cdf] / [split_or_vert_cdf] binary-CDF derivation, r150’s §9.3 [PARTITION_SUBSIZE] table + [partition_subsize] accessor, and the §9.3 [MI_WIDTH_LOG2] / [NUM_4X4_BLOCKS_WIDE] tables into one [PartitionWalker] type. The walker carries the §6.10.4 MiSizes[r][c] grid (filled at every leaf via the block’s [NUM_4X4_BLOCKS_WIDE] / [NUM_4X4_BLOCKS_HIGH] footprint), and consults it for the §8.3.2 [partition_ctx] derivation above = AvailU && (Mi_Width_Log2[ MiSizes[r-1][c] ] < bsl) / left = AvailL && (Mi_Height_Log2[ MiSizes[r][c-1] ] < bsl) on every recursive child (av1-spec p.362). The walker emits a Vec<DecodedBlockRecord> of (MiRow, MiCol, MiSize) leaves in §5.11.4 syntax order; the actual §5.11.5 decode_block() body remains out of scope and is the next round’s target. All four §5.11.4 edge-of-frame branches are honoured: the r >= MiRows || c >= MiCols early return; the bSize < BLOCK_8X8 short-circuit to PARTITION_NONE with no symbol read; the hasCols-alone branch that reads split_or_horz; the hasRows-alone branch that reads split_or_vert; and the !hasRows && !hasCols fall-through to PARTITION_SPLIT. All ten partition arms (NONE / HORZ / VERT / SPLIT / HORZ_A / HORZ_B / VERT_A / VERT_B / HORZ_4 / VERT_4) dispatch the spec’s literal decode_block / recursive decode_partition calls with the appropriate subSize (the Partition_Subsize[ partition ][ bSize ] lookup) or splitSize (the Partition_Subsize[ PARTITION_SPLIT ][ bSize ] lookup). New [TileGeometry] type carries the four §5.11.1 mi-unit tile bounds for the §5.11.51 is_inside test. The §5.11.4 bottom-right edge clip on the optional HORZ_4 / VERT_4 fourth leaf (r + quarterBlock4x4 * 3 < MiRows / c + quarterBlock4x4 * 3 < MiCols) is applied literally. Out-of-range / out-of-tile inputs surface as Error::PartitionWalkOutOfRange (caller-bug only — a conformant driver never produces one). Tests cover: single-leaf PARTITION_NONE for sub-BLOCK_8X8 block sizes (no symbol read); single-leaf and split-emission against the W128 superblock; recursive descent down to BLOCK_4X4 leaves; all ten partition arms via deterministic CDF setups; the edge-of-frame hasRows-alone / hasCols-alone branches via a small mi-cropped frame; the §6.10.4 MiSizes[] grid-fill invariant (every cell of the leaf’s bh4 * bw4 footprint carries sub_size); and the §5.11.4 r >= MiRows || c >= MiCols early-return invariant. The walker leaves the decode_block coefficient / motion-vector / reconstruction path entirely to the next round.

• Round 152. The §5.11.11 read_skip() syntax element (av1-spec p.65) — the per-block skip syntax read. Lands as a new [PartitionWalker::decode_skip] method on the r151 walker, plus a Skips[r][c] flag grid carried alongside the existing §6.10.4 MiSizes[] grid. Both spec branches are honoured: when the caller passes seg_skip_active = true (the combined precondition SegIdPreSkip && seg_feature_active( SEG_LVL_SKIP ) from §5.9.14 segmentation state, computed upstream by the frame parser), the spec short-circuits to skip = 1 with no symbol read; otherwise an S() symbol is decoded against TileSkipCdf[ctx] where ctx = AvailU * Skips[MiRow-1][MiCol] + AvailL * Skips[MiRow][MiCol-1] per av1-spec p.378, driven through the walker’s Skips[] grid and [TileGeometry::is_inside] for AvailU / AvailL. The §5.11.5 grid-fill (av1-spec p.65 footer) stamps the decoded value over the block’s bw4 * bh4 footprint, clipped at the frame’s MiRows / MiCols extent. New [PartitionWalker::skips] accessor returns a row-major view of the grid for downstream §5.11.x consumers. Out-of-range mi_row / mi_col / sub_size surface as Error::PartitionWalkOutOfRange. Tests cover: seg short-circuit no-symbol-read invariant; else-branch S() against rigged 2-symbol CDFs (forced 0 and 1); footprint grid-stamp on both branches; ctx-0 selection at the frame origin (AvailU = AvailL = false); ctx-2 selection through two prior Skips=1 neighbours; AvailL-false at the left-tile-column boundary; non-zero tile origin clearing both AvailU / AvailL; right-edge bw4 clip; out-of-range guard returns; and the initial all-zero Skips[] invariant. 394 -> 405 tests, zero #[ignore].

• Round 154. The §5.11.10 read_skip_mode() syntax element (av1-spec p.67) — the per-block skip_mode syntax read. Lands as a new [PartitionWalker::decode_skip_mode] method on the r152 walker, plus a SkipModes[r][c] flag grid carried alongside the r152 Skips[] and the existing §6.10.4 MiSizes[] grids. The §5.11.10 short-circuit set (any-true ⇒ skip_mode = 0, no symbol read) is honoured: seg_feature_active(SEG_LVL_SKIP / REF_FRAME / GLOBALMV) collapsed into the caller-provided seg_skip_mode_off; !skip_mode_present via the §5.9.21 frame-header scalar; and Block_Width[MiSize] < 8 || Block_Height[MiSize] < 8 derived locally from sub_size via the §9.3 [cdf::block_width] / [cdf::block_height] tables. Otherwise an S() symbol is decoded against TileSkipModeCdf[ctx] with ctx = AvailU * SkipModes[MiRow-1][MiCol] + AvailL * SkipModes[MiRow][MiCol-1] per av1-spec p.378, routed through the existing [skip_mode_ctx] helper. The §5.11.5 grid-fill stamps the value over the block’s bw4 * bh4 footprint, clipped at the frame’s MiRows / MiCols extent. New [PartitionWalker::skip_modes] accessor returns a row-major view. skip_mode is the inter-frame compound-reference shortcut read in §5.11.18 inter_frame_mode_info before the rest of the inter mode decode (intra-only frames never call this). Tests cover: seg short-circuit; skip_mode_present false short-circuit; both Block_Width-and-Block_Height < 8 short-circuits via BLOCK_4X8 and BLOCK_8X4; else-branch S() against rigged 2-symbol CDFs (forced 0 and 1); footprint grid-stamp; ctx-0 selection at the frame origin; ctx-1 single-neighbour and ctx-2 both-neighbour selection; non-zero tile origin clearing AvailU / AvailL; right-edge bw4 clip; out-of-range guard returns; and the initial all-zero SkipModes[] invariant. 405 -> 417 tests, zero #[ignore].

• Round 155. The §5.11.12 read_delta_qindex() syntax element (av1-spec p.67) — the per-superblock quantiser index delta read. Lands as a new [PartitionWalker::decode_delta_qindex] method on the r154 walker, plus a CurrentQIndex scalar tracked across calls via [PartitionWalker::current_q_index] / [PartitionWalker::set_current_q_index]. Honours the §5.11.12 superblock-skip short-circuit (MiSize == sbSize && skip ⇒ no symbol read; sbSize derived from the §5.5.1 use_128x128_superblock flag) and the outer ReadDeltas (§6.10.4) gate. Otherwise an S() symbol is decoded against TileDeltaQCdf (a single-row §8.3.2 CDF, no context index, length DELTA_Q_SMALL + 2 = 5); a decoded value of DELTA_Q_SMALL = 3 triggers the §5.11.12 escape ladder (delta_q_rem_bits L(3) + post-increment + delta_q_abs_bits L(rem_bits + 1)), reconstructing the absolute value via delta_q_abs = delta_q_abs_bits + (1 << n) + 1 over the extended range 0..=2 ∪ 3..=511. Non-zero delta_q_abs reads delta_q_sign_bit L(1) and applies the spec’s CurrentQIndex = Clip3(1, 255, CurrentQIndex + (reducedDeltaQIndex << delta_q_res)) update. New constant [cdf::DELTA_Q_SMALL] (= 3) plus new table [cdf::DEFAULT_DELTA_Q_CDF] transcribed verbatim from §9.4 p.431 ([28160, 32120, 32677, 32768, 0]); new field [cdf::TileCdfContext::delta_q] + accessor [cdf::TileCdfContext::delta_q_cdf]. Tests cover: default CDF literal match; init-from-defaults invariant; sb-skip short-circuit for both use_128x128_superblock values; ReadDeltas false short-circuit; zero delta_q_abs no-update; literal-positive paths with and without shift; Clip3 lower-bound via hostile seed; Clip3 upper-bound; DELTA_Q_SMALL escape ladder minimum value; escape ladder stays in Clip3(1, 255) range; cross-call accumulation; fresh-walker initial CurrentQIndex = 0; out-of-range guard; arithmetic decoder zero-byte sign-bit observation. 417 -> 433 tests, zero #[ignore].

• Round 156. The §5.11.13 read_delta_lf() syntax element (av1-spec p.68) — the per-superblock loop-filter delta read, structurally parallel to §5.11.12 but iterating frameLfCount times over a four-slot DeltaLF[ i ] accumulator with the delta_lf_multi flag selecting between the §8.3.2 single-LF (TileDeltaLFCdf) and per-edge multi-LF (TileDeltaLFMultiCdf[ i ]) cdf branches. Lands as a new [PartitionWalker::decode_delta_lf] method plus a current_delta_lf: [i32; FRAME_LF_COUNT] accumulator on the walker (accessors [PartitionWalker::current_delta_lf] and [PartitionWalker::reset_current_delta_lf] for the §5.11.2 tile-entry reset). Honours the §5.11.13 superblock-skip short-circuit identically to §5.11.12, plus the ReadDeltas && delta_lf_present outer gate (two AND-ed flags). When the gate passes, frameLfCount is derived locally: delta_lf_multi == 0 ⇒ 1; delta_lf_multi == 1 && mono_chrome ⇒ FRAME_LF_COUNT - 2 = 2; otherwise FRAME_LF_COUNT = 4. Each iteration reads delta_lf_abs S() against the branch-selected CDF, then either the literal value or the §5.11.13 escape ladder (delta_lf_rem_bits L(3) + post-increment + delta_lf_abs_bits L(rem_bits + 1) ⇒ deltaLfAbs = abs_bits + (1 << n) + 1), then for non-zero magnitudes delta_lf_sign_bit L(1) followed by the DeltaLF[ i ] = Clip3(-MAX_LOOP_FILTER, MAX_LOOP_FILTER, DeltaLF[ i ] + (reducedDeltaLfLevel << delta_lf_res)) update. New constants [cdf::DELTA_LF_SMALL] (= 3), [cdf::FRAME_LF_COUNT] (= 4), and [cdf::MAX_LOOP_FILTER] (= 63 as i32 — distinct from the pre-existing uncompressed_header_tail::MAX_LOOP_FILTER i16 twin used by §5.9.11). New table [cdf::DEFAULT_DELTA_LF_CDF] transcribed verbatim from §9.4 p.431 ([28160, 32120, 32677, 32768, 0], equal to DEFAULT_DELTA_Q_CDF per the spec listing — preserved as two independent constants so adaptation drift on one does not leak through the other). New fields [cdf::TileCdfContext::delta_lf] + [cdf::TileCdfContext::delta_lf_multi] with accessors [cdf::TileCdfContext::delta_lf_cdf] / [cdf::TileCdfContext::delta_lf_multi_cdf]. 17 new cdf-module tests (433 -> 450): default-CDF literal match (incl. §9.4 equality with DEFAULT_DELTA_Q_CDF); init-from-defaults invariant for both single-LF and all four multi-LF rows; sb-skip short-circuit (64x64 and 128x128); ReadDeltas false short-circuit; delta_lf_present false short-circuit; single-LF branch writes only DeltaLF[0]; multi-LF colour branch writes all four slots; multi-LF monochrome branch writes only the two Y slots; zero-delta_lf_abs no-update; literal-positive with shift; Clip3 upper-bound at MAX_LOOP_FILTER = 63; Clip3 lower-bound via hostile seed; DELTA_LF_SMALL escape ladder minimum value; cross-call accumulation; fresh-walker initial accumulator all-zero + reset_current_delta_lf round-trip; out-of-range guard. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 157. The §5.11.56 read_cdef() syntax element (av1-spec p.104) — the per-leaf CDEF-index read, plus the §5.11.55 clear_cdef() per-superblock sentinel reset. Lands as new [PartitionWalker::decode_cdef] + [PartitionWalker::clear_cdef] methods on the r156 walker, plus a cdef_idx: Vec<i8> row-major grid sized MiRows × MiCols with [PartitionWalker::cdef_idx] read accessor. CDEF operates on 64×64 anchor cells, so the walker masks the leaf (MiRow, MiCol) to the anchor at (MiRow & cdefMask4, MiCol & cdefMask4) (cdefMask4 = ~(cdefSize4 - 1), cdefSize4 = Num_4x4_Blocks_Wide[ BLOCK_64X64 ] = 16) and uses the anchor’s -1 sentinel to decide whether the first leaf in this anchor should read an L(cdef_bits) literal (cdef_bits in 0..=3 per §5.9.19 f(2)). When the literal is read, the grid-fill loop stamps the value across the leaf’s (w4, h4) footprint at the cdefSize4 = 16 stride so super-64 blocks (BLOCK_128X128) reach all four anchor cells while sub-64 blocks touch only their containing anchor. Subsequent leaves in the same 64×64 anchor short-circuit (no read; the anchor already holds the value). The §5.11.56 short-circuit set is honoured: skip || CodedLossless || !enable_cdef || allow_intrabc ⇒ no read, anchor sentinel/value returned unchanged. clear_cdef( r, c, use_128x128_superblock ) — called by the §5.11.2 tile walk before each superblock — stamps -1 at the one (64×64 superblocks) or four (128×128 superblocks) anchor cells; out-of-grid anchors are silently skipped (the bottom/right superblock can straddle the frame edge). 18 new cdf-module tests (450 → 468): fresh-walker all--1 invariant; clear_cdef 64x64 single-anchor stamp; clear_cdef 128x128 four-anchor stamp; clear_cdef out-of-grid skip; each of the four skip / CodedLossless / !enable_cdef / allow_intrabc short-circuit gates; first-leaf-reads-literal-and-stamps-anchor; second-leaf-in- anchor-no-read; cdef_bits == 0 zero-bit stamp; cdef_bits == 3 upper-bound; anchor-mask routes (10, 13) ⇒ (0, 0); BLOCK_128X128 stamps all four anchors; grid-fill clips at frame edge; short-circuit returns prior stamp; clear_cdef after stamp resets anchor; out-of-range guard (4-way: mi_row / mi_col / sub_size / cdef_bits > 3). decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 158. The §5.11.20 read_is_inter() syntax element (av1-spec p.71-72) — the per-block intra/inter classifier read inside §5.11.18 inter_frame_mode_info (after inter_segment_id / read_skip / read_cdef / read_delta_qindex / read_delta_lf) that dispatches between §5.11.22 intra_block_mode_info and §5.11.23 inter_block_mode_info. Lands as a new [PartitionWalker::decode_is_inter] method on the r157 walker, plus an IsInters[r][c] flag grid carried alongside the r157 cdef_idx[], r154 SkipModes[], r152 Skips[], and the existing §6.10.4 MiSizes[] grids (IsInters[ r + y ][ c + x ] = is_inter per the §5.11.5 footer at av1-spec p.65). All four arms of the §5.11.20 dispatch are honoured in spec order (first match fires, no read on the short-circuit arms): Arm 1 — skip_mode == 1 forces is_inter = 1; Arm 2 — seg_feature_active(SEG_LVL_REF_FRAME) routes through the caller-pre-computed FeatureData[segment_id][SEG_LVL_REF_FRAME] != INTRA_FRAME boolean (the walker stays segmentation-state-free, identical to r154’s seg_skip_mode_off pattern); Arm 3 — seg_feature_active(SEG_LVL_GLOBALMV) forces is_inter = 1; Arm 4 — S() symbol read against TileIsInterCdf[ctx] with ctx from the existing [is_inter_ctx] helper. The §8.3.2 ctx samples neighbour intra-ness from the complement of the walker’s IsInters[] grid (intra = !is_inter), with an unavailable neighbour treated as intra per §5.11.18 (LeftRefFrame[0] = AvailL ? RefFrames[..][0] : INTRA_FRAME ⇒ None to [is_inter_ctx]). The §5.11.5 grid-fill stamps the value over the block’s bw4 * bh4 footprint, clipped at the frame’s MiRows / MiCols extent. New [PartitionWalker::is_inters] accessor returns a row-major view. 15 new cdf-module tests (468 → 483): fresh-walker grid all-zero; Arm 1 skip_mode short-circuit (position-invariant on a hostile 0xFF buffer); Arm 2 routing to intra and to inter (both position-invariant); Arm 3 globalmv short-circuit; Arm 1 takes precedence over Arm 2 / Arm 3; Arm 2 takes precedence over Arm 3; else-branch S() returning symbol 0 / 1 on rigged binary CDF rows (symbol-1 verifies the footprint grid-stamp); ctx-0 / ctx-1 / ctx-2 / ctx-3 selection through intra/inter seed combinations and a mi_col_start = 4 tile origin; bottom-right edge clip on BLOCK_16X16 @ (2, 2) in a 4×4 frame; three-way out-of-range guard ⇒ PartitionWalkOutOfRange. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 159. The §5.11.9 read_segment_id() syntax element (av1-spec p.66) — the per-block segment-id reader called inside §5.11.8 intra_segment_id and §5.11.19 inter_segment_id whenever segmentation_enabled. Lands as a new [PartitionWalker::decode_segment_id] method on the r158 walker, plus a SegmentIds[r][c] grid carried alongside the r158 IsInters[], r156 cdef_idx[], r154 SkipModes[], r152 Skips[], and the existing §6.10.4 MiSizes[] grids (SegmentIds[ r + y ][ c + x ] = segment_id per the §5.11.5 grid-fill footer). The grid is pre-filled with the §5.11.9 -1 sentinel; cells inside a decoded block’s bh4 * bw4 footprint then carry segment_id in 0..MAX_SEGMENTS = 0..8. The §5.11.9 neighbour cascade is honoured exactly as spelled out: prevUL requires both AvailU AND AvailL; prevU and prevL each gate on their own edge; out-of-grid neighbours fall through to -1. The four-arm pred derivation (prevU == -1 ⇒ prevL / 0; prevL == -1 ⇒ prevU; prevUL == prevU ⇒ prevU; else prevL) is preserved verbatim. The §5.11.9 dispatch distinguishes two paths: skip != 0 ⇒ segment_id = pred (zero bits read); else diff S() against TileSegmentIdCdf[ctx] (ctx from the existing [segment_id_ctx] helper) then segment_id = neg_deinterleave(diff, pred, last_active_seg_id + 1). The walker stays segmentation-state-free: the caller passes last_active_seg_id (the §5.9.14 trailing derivation) and the skip value the §5.11.11 decode_skip just returned. New public module-level [neg_deinterleave] helper transcribes the §5.11.9 bijection. New [PartitionWalker::segment_ids] accessor returns a row-major view. 11 new cdf-module tests (483 → 494): fresh-walker grid all -1; skip short-circuit at frame origin writes segment_id = pred = 0 (no S() bit consumed on a hostile 0xFF byte buffer); skip inherits prev_u when prev_l is unavailable; non-skip path with pred = 0 returns diff unchanged; direct neg_deinterleave table exercises for both 2 * ref < max and 2 * ref >= max branches plus edge cases (ref == 0 identity, ref == max - 1 inverted, smallest non-trivial alphabet max = 2); ctx-0 origin selection; ctx-2 all-neighbours-match selection through three walker-stamped seeds; bottom-right edge clip on BLOCK_16X16 @ (2, 2) in a 4×4 frame; four-way out-of-range guard. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 160. The §5.11.8 intra_segment_id() syntax element (av1-spec p.66) — the intra-frame variant of the per-block segment-id read, called from §5.11.7 intra_frame_mode_info on both the SegIdPreSkip and !SegIdPreSkip arms. Lands as a new [PartitionWalker::decode_intra_segment_id] method that dispatches on the caller-passed segmentation_enabled bit: when set, descends into r159 [PartitionWalker::decode_segment_id] (which does the §5.11.9 neighbour cascade + skip / non-skip dispatch + grid fill); when clear, stamps segment_id = 0 over the leaf’s bh4 * bw4 footprint without reading any bits. Both arms then resolve the §5.11.8 Lossless = LosslessArray[ segment_id ] lookup via a caller-supplied lossless_array: &[bool; MAX_SEGMENTS] (the §6.8.2 per-segment table the frame-header walk computes from qindex + DeltaQ?Dc + DeltaQ?Ac). Returns (segment_id, lossless). The walker stays segmentation-state-free: callers pass segmentation_enabled, last_active_seg_id, and lossless_array per-call (matching the r159 pattern). Range guards (out-of-range sub_size, mi_row / mi_col past the frame’s mi extent, last_active_seg_id >= MAX_SEGMENTS) fire on both arms so the no-symbol path is total over the same input space as the bitstream-reading path. 7 new cdf-module tests (494 → 501): segmentation_enabled = false no-read on a hostile 0xFF buffer with lossless_array[0] = true and = false arms; segmentation_enabled = true, skip = 1 at frame origin (pred = 0, no S() consumed); segmentation_enabled = true, skip = 0 reading diff = 3 on a rigged CDF and looking up lossless_array[3]; per-segment Lossless indexing (rig diff = 5, set lossless_array[5] = false while every other slot is true, expect Lossless = false); bottom-right edge-clip on BLOCK_16X16 @ (2, 2) in a 4×4 frame on the !segmentation_enabled arm; five-way out-of-range guard covering both arms. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 161. The §5.11.7 intra_frame_mode_info() prefix dispatcher (av1-spec p.64) — the per-block top-level entry-point that composes the §5.11.7 first 11 lines: skip = 0; conditional pre-skip intra_segment_id(); skip_mode = 0; read_skip(); conditional post-skip intra_segment_id(); read_cdef(); read_delta_qindex(); read_delta_lf(); the fixed ReadDeltas = 0 / RefFrame[0] = INTRA_FRAME / RefFrame[1] = NONE assignments. Lands as a new [PartitionWalker::decode_intra_frame_mode_info_prefix] method on the r160 walker, returning the new public [cdf::IntraFrameModeInfoPrefix] struct carrying every post-call observable (skip, skip_mode, segment_id, lossless, cdef_idx, current_q_index, current_delta_lf, ref_frame). The §5.11.7 SegIdPreSkip conditional routes the §5.11.8 call before or after the §5.11.11 read_skip() per the caller-passed seg_id_pre_skip boolean (the §5.9.14 trailing derivation). skip_mode is fixed at 0 because the intra-frame walk never calls decode_skip_mode (§5.11.10 short-circuits on !skip_mode_present for intra-only frames per §5.9.21). The §6.10.4 ReadDeltas = 0 assignment is left to the caller (the walker remains stateless about per-superblock first-block detection), matching the §6.10.4 pattern existing [PartitionWalker::decode_delta_qindex] / [PartitionWalker::decode_delta_lf] call sites already use. Range guards (out-of-range sub_size, mi_row / mi_col, last_active_seg_id >= MAX_SEGMENTS, cdef_bits > 3) fire on the dispatcher level before any inner read so a caller bug never produces a partial-read. 8 new cdf-module tests (501 → 509): minimum-bit path (one S() consumed for read_skip); SegIdPreSkip = true arm reading segment_id first then skip; SegIdPreSkip = false arm post-skip with skip = 1 triggering the §5.11.9 short-circuit; seg-skip-active forcing skip = 1 with zero bits consumed on a hostile 0xFF buffer; fixed ref_frame = [INTRA_FRAME, NONE]; read_deltas true wiring through to both delta_q and delta_lf reads; five-way out-of-range guard; skip_mode always 0 on both pre-skip arms (verifies SkipModes[] grid untouched). The §5.11.7 follow-on body (use_intrabc arm + intra_block_mode_info composite) and the §5.11.18 inter_frame_mode_info / §5.11.19 inter_segment_id two-call protocol remain the next round’s targets. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 162. The §5.11.19 inter_segment_id( preSkip ) syntax element (av1-spec p.71) — the inter-frame variant of the per-block segment-id read, called twice per block from §5.11.18 (once before §5.11.11 read_skip() with preSkip = 1 and once after with preSkip = 0). Lands as a new [PartitionWalker::decode_inter_segment_id] method. New SEGMENT_ID_PREDICTED_CONTEXTS = 3 (§9.3) constant and [cdf::DEFAULT_SEGMENT_ID_PREDICTED_CDF] table verbatim from §9.4 (av1-spec p.442 — three uniform [128 * 128, 32768, 0] rows for the binary seg_id_predicted symbol). New [cdf::TileCdfContext::segment_id_predicted] field initialised from DEFAULT_SEGMENT_ID_PREDICTED_CDF plus the [cdf::TileCdfContext::segment_id_predicted_cdf] selector implementing the §8.3.2 TileSegmentIdPredictedCdf[ ctx ] index. New persistent above_seg_pred_context (length mi_cols) and left_seg_pred_context (length mi_rows) buffers on PartitionWalker per the §8.3.1 tile-entry initialisation; the §8.3.2 ctx walk reads LeftSegPredContext[ MiRow ] + AboveSegPredContext[ MiCol ] (each 0..=1; sum 0..=2 < SEGMENT_ID_PREDICTED_CONTEXTS). [PartitionWalker::above_seg_pred_context] / [PartitionWalker::left_seg_pred_context] accessors surface the arrays. The dispatcher routes the full §5.11.19 cascade exactly: outer !segmentation_enabled collapses to segment_id = 0; inner !segmentation_update_map adopts predictedSegmentId; pre_skip && !SegIdPreSkip early-exit returns segment_id = 0; the post-skip skip != 0 arm zeroes the context arrays then descends into decode_segment_id (the §5.11.9 skip short-circuit fires inside); the segmentation_temporal_update == 1 arm reads seg_id_predicted, branches to predictedSegmentId adopt or read_segment_id(), and stamps the context arrays with the just-read flag; the temporal_update == 0 fall-through reads read_segment_id() without touching the context arrays (per spec). predicted_segment_id (§5.11.21 get_segment_id()) is caller-supplied from the §6.10 reference-frame walk so the walker stays inter-frame-state-free. Range guards (out-of-range sub_size, mi_row/mi_col past extent, last_active_seg_id >= MAX_SEGMENTS, and the new predicted_segment_id > last_active_seg_id invariant) fire up-front on every arm. 11 new cdf-module tests (509 → 520): fresh-walker context-array zeroing; !segmentation_enabled no-read on both pre/post-skip arms; !segmentation_update_map predicted-id adoption; pre_skip && !SegIdPreSkip early-exit; post-skip + skip != 0 zeroing context arrays then descending into the §5.11.9 short-circuit (poisoned context arrays prove the spec write fires); temporal_update == 1 + rigged seg_id_predicted = 1 adopting predicted id and stamping context to 1; temporal_update == 1 + rigged seg_id_predicted = 0 descending into decode_segment_id and stamping context to 0; temporal_update == 0 fall-through leaving context untouched; five-way out-of-range guard; Default_Segment_Id_Predicted_Cdf layout; the segment_id_predicted_cdf accessor round-trip. The §5.11.18 inter_frame_mode_info() top-level dispatcher remains the next round’s architectural payoff. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 163. The §5.11.21 get_segment_id() pure-helper function (av1-spec p.72) — the inter-frame per-block segment-id prediction lookup that scans the previous frame’s PrevSegmentIds[][] over the on-screen window covered by the current block and returns the smallest id found. Lands as a new free function [cdf::get_segment_id] (re-exported at the crate root) that takes the previous-frame segmentation surface as a row-major &[i32] slice plus its (prev_mi_rows, prev_mi_cols) extent, the current frame’s mi-extent (mi_rows, mi_cols) and anchor (mi_row, mi_col), and the block’s sub_size (§3 BLOCK_* ordinal). Returns Some(seg) with the §5.11.21 Min reduction result over xMis = Min(MiCols - MiCol, bw4) × yMis = Min(MiRows - MiRow, bh4) cells; seg is in -1..=7 (the -1 sentinel surfaces when an unwritten previous-frame cell falls inside the window, letting callers detect a malformed reference surface via the existing §5.11.19 predicted_segment_id > last_active_seg_id range guard). Returns None for caller-bug arguments (out-of-range sub_size, anchor outside the current frame, previous-frame extent smaller than the current frame’s, or prev_segment_ids length not matching prev_mi_rows * prev_mi_cols). The function is pure (no walker state, no bitreader, no CDF) and complements the r162 [cdf::PartitionWalker::decode_inter_segment_id] caller — which takes a pre-computed predicted_segment_id: u8 so the walker can stay inter-frame-state-free — by giving the §6.10 reference-frame walk a verbatim spec-shaped routine to compute that argument from PrevSegmentIds[]. 12 new cdf-module tests (520 → 532): uniform-0 / uniform-7 reductions over several block sizes; explicit Min-over-2x2-window cells with out-of-window decoy values that must not contribute; frame-edge xMis/yMis clipping on a BLOCK_16X16 anchored at the bottom-right of a 4x4 mi-grid; -1 sentinel round-trip; a wider-than-current previous frame exercising the prev_mi_cols row stride; single-cell BLOCK_4X4 covering exactly prev[MiRow][MiCol] with a neighbour-cell decoy; out-of-range guards for invalid sub_size, anchor past frame extent, previous-frame extent smaller than current frame’s, and length / shape mismatch; an end-to-end composition test feeding get_segment_id’s result into decode_inter_segment_id’s no-read !segmentation_update_map arm and verifying the predicted id is adopted with zero bit reads on a hostile 0xFF buffer. The §5.11.18 inter_frame_mode_info() top-level dispatcher, §5.11.7 use_intrabc arm, and §5.11.22 intra_block_mode_info composite remain the next round’s targets. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 168. §5.11.17 read_var_tx_size() (av1-spec p.70) + §5.11.18 inter_frame_mode_info() (av1-spec p.71) — the two missing inter-arm composites that bound the §5.11.5 walker’s inter side. The §5.11.17 reader is exposed as [cdf::PartitionWalker::read_var_tx_size] (callable standalone) and wired into the §5.11.16 inter-arm so [cdf::PartitionWalker::read_block_tx_size] no longer surfaces Error::ReadVarTxSizeUnsupported on the TX_MODE_SELECT && is_inter && !skip && !Lossless arm — the recursion stamps InterTxSizes[] per terminal-else leaf and the outer §5.11.5 footer stamps TxSizes[] over the full block footprint. The §8.3.2 txfm_split ctx selector inlines the spec’s get_above_tx_width / get_left_tx_height helpers as private [cdf::PartitionWalker] methods against the walker’s Skips[] / IsInters[] / MiSizes[] / InterTxSizes[] grids, and routes the (above, left, txSzSqrUp, maxTxSz) derivation through the existing [cdf::txfm_split_ctx] helper. New free function [cdf::find_tx_size] (§5.11.36 helper, re-exported) supports the maxTxSz = find_tx_size(size, size) step of the ctx formula.

  The §5.11.18 reader is exposed as [cdf::PartitionWalker::decode_inter_frame_mode_info] composing every leaf already wired through the walker: [cdf::PartitionWalker::decode_inter_segment_id] (pre- and post-skip arms), [cdf::PartitionWalker::decode_skip_mode], [cdf::PartitionWalker::decode_skip] (gated by skip_mode == 0), [cdf::PartitionWalker::decode_cdef], [cdf::PartitionWalker::decode_delta_qindex], [cdf::PartitionWalker::decode_delta_lf], and [cdf::PartitionWalker::decode_is_inter]. The terminal if (is_inter) dispatch short-circuits at two new Error variants: Error::InterBlockModeInfoUnsupported (§5.11.23 inter_block_mode_info() — the next-round target for the MV stack / ref-frame readers) and Error::IntraBlockModeInfoUnsupported (§5.11.22 intra_block_mode_info() — the next-round target for the per-block intra angle / UV mode readers). New [cdf::DecodedInterFrameModeInfo] aggregate carries every §5.11.18 derived value.

  The §5.11.5 [cdf::PartitionWalker::decode_block_syntax] walker is unchanged on the frame_is_intra = false arm — it still surfaces Error::DecodeBlockInterFrameUnsupported (the umbrella stub) because the §5.11.18 reader needs additional caller state (segmentation_update_map / segmentation_temporal_update / predicted_segment_id / seg_*_active overrides / skip_mode_present) the §5.11.5 driver doesn’t yet thread through. Direct callers of decode_inter_frame_mode_info get the full pre-dispatch walk and the §5.11.22 / §5.11.23 distinction.

  11 new integration tests cover the §5.11.17 base case + depth cap + split path + frame-edge clip + caller-bug guards + the wired §5.11.16 inter-arm, plus the §5.11.18 intra / inter stub dispatch + skip-mode-forces-skip + segment-globalmv arm + caller-bug guards + the DecodedInterFrameModeInfo public-API smoke. Plus 1 new unit test for find_tx_size. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 167. The §5.11.16 read_block_tx_size() reader (av1-spec p.70) — the per-block transform-size syntax-tree read that r166’s §5.11.5 walker hit as the first stub on the intra arm. Lands as a new [cdf::PartitionWalker::read_block_tx_size] method (callable standalone) and is wired into the §5.11.5 walker so the walker now reaches Error::DecodeBlockComputePredictionUnsupported (§5.11.30) instead.

  The reader transcribes the spec body one-to-one. The outer TX_MODE_SELECT && MiSize > BLOCK_4X4 && is_inter && !skip && !Lossless arm routes to §5.11.17 read_var_tx_size (the next-arc target — surfaces a new Error::ReadVarTxSizeUnsupported). The else arm inlines §5.11.15 read_tx_size(!skip || !is_inter): a Lossless short-circuit forces TxSize = TX_4X4; otherwise TxSize starts at Max_Tx_Size_Rect[ MiSize ] and is further split via Split_Tx_Size[] for tx_depth iterations when the §5.11.15 MiSize > BLOCK_4X4 && allowSelect && TxMode == TX_MODE_SELECT gate fires. The §8.3.2 tx_depth ctx walks the neighbour IsInters[] / MiSizes[] / InterTxSizes[] ladder per get_above_tx_width / get_left_tx_height and selects the CDF row via Max_Tx_Depth[ MiSize ]. The else-arm grid-fill stamps both [cdf::PartitionWalker::inter_tx_sizes] and the §5.11.5 footer’s [cdf::PartitionWalker::tx_sizes] across the block footprint.

  New spec tables ([cdf::MAX_TX_SIZE_RECT] / [cdf::MAX_TX_DEPTH_TABLE] / [cdf::SPLIT_TX_SIZE] / [cdf::MAX_VARTX_DEPTH]) and 14 new rectangular TX_* ordinals ([cdf::TX_4X8] / … / [cdf::TX_64X16]) transcribe av1-spec p.402, p.69, p.404, §3 p.7, and §6.10.16 respectively. New [cdf::PartitionWalker] grids tx_sizes / inter_tx_sizes cover §5.11.5 / §5.11.16 write semantics. [cdf::DecodedBlock] gains a tx_size field; [cdf::PartitionWalker::decode_block_syntax] gains a tx_mode_select: bool parameter (threaded from the §5.9.21 / §6.8.21 frame-header TxMode derivation).

  10 new integration tests cover the new reader’s spec paths; 5 new unit tests verify the spec tables. decode_av1 / encode_av1 continue to return Error::NotImplemented.

• Round 166. The §5.11.5 decode_block() syntax-walker skeleton (av1-spec p.63-64) — the missing dispatcher that the §5.11.4 partition walker recurses into at every leaf. Lands as a new [cdf::PartitionWalker::decode_block_syntax] method that performs the §5.11.5 prologue (MiRow, MiCol, MiSize, bw4, bh4; the HasChroma three-arm dispatch on bh4 == 1 && subsampling_y && (MiRow & 1) == 0 and bw4 == 1 && subsampling_x && (MiCol & 1) == 0; AvailU, AvailL, AvailUChroma, AvailLChroma derivation with the spec’s chroma fix-up arm) and the §5.11.6 mode_info() intra arm composed from r161’s [cdf::PartitionWalker::decode_intra_frame_mode_info_prefix], r164’s [cdf::PartitionWalker::decode_use_intrabc], and r165’s [cdf::PartitionWalker::decode_intra_frame_y_mode]. The §5.11.49 palette_tokens() call is a no-op on the no-palette path. Short-circuits at the §5.11.16 read_block_tx_size() call with a new Error::DecodeBlockReadBlockTxSizeUnsupported — the immediate next-round target.

  Four new Error variants surface the §5.11.5 next-round boundaries one-to-one: Error::DecodeBlockInterFrameUnsupported (§5.11.18 inter_frame_mode_info(), fires on frame_is_intra = false with zero bits consumed); Error::DecodeBlockReadBlockTxSizeUnsupported (§5.11.16, the stub the walker actually reaches); Error::DecodeBlockComputePredictionUnsupported (§5.11.30, reserved for the round that lands §5.11.16); and Error::DecodeBlockResidualUnsupported (§5.11.34, reserved for the round that lands §5.11.30).

  New [cdf::DecodedBlock] per-block aggregate — publicly constructible — carries the §5.11.5 prologue + §5.11.7 mode-info derivations on the no-stub path. Reachable once §5.11.16 lands.

  §5.11.4 partition driver mirror: [cdf::PartitionWalker::decode_partition_syntax] walks the same recursion shape as [cdf::PartitionWalker::decode_partition] but routes every leaf through decode_block_syntax instead of the leaf-only emitter. Stub propagates from the first leaf that fires it.

  10 new integration tests (tests/decode_block_syntax_walker.rs) cover the §5.11.5 prologue’s three-arm HasChroma dispatch on BLOCK_4X4, the §5.11.6 inter-arm stub, the §5.11.7 SegIdPreSkip pre-skip arm reaching the §5.11.16 stub after the composed reads fire in spec order, out-of-range guards, the §5.11.4 partition driver’s BLOCK_4X4 short-circuit arm propagating the stub, the §5.11.4 r >= MiRows line-1 early return, DecodedBlock public-API constructibility, BLOCK_8X16 grid-fill footprint (bw4 = 2, bh4 = 4), and BLOCK_16X16 with cdef_bits = 2 exercising the §5.11.56 literal-bits read.

  The §5.11.7 follow-on else-arm elements (intra_angle_info_y, uv_mode, read_cfl_alphas, intra_angle_info_uv, palette_mode_info, filter_intra_mode_info) and the use_intrabc == 1 MV-stack / assign-mv body remain bounded leaf targets that can be slotted into a future round before or alongside §5.11.16. decode_av1 / encode_av1 continue to return Error::NotImplemented.

Tile-group / tile-content decode (the per-tile coefficient, motion-vector, and reconstruction passes) remains out of scope, as does the §7.20 reference frame update process that would store a decoded frame back into [frame_header::RefInfo] across frames. decode_av1 / encode_av1 continue to return Error::NotImplemented.

Re-exports

pub use codec_config::Av1CodecConfig;

Modules

annexb

Annex B length-delimited bitstream format (read + write).

codec_config

The AV1 codec-configuration fields a container carries next to an elementary stream — the av1C record every AVIF / HEIF av01 item and every ISOBMFF av01 sample entry is required to carry (av1-avif §2.2.1: “the values of the fields in the AV1ItemConfigurationProperty shall match those of the Sequence Header OBU in the AV1 Image Item Data”).

decoder

Decoder side of the crate.

encoder

Encoder side of the crate.

registry

oxideav-core framework integration: codec registration plus the oxideav_core::Decoder implementation that bridges the crate’s spec-faithful frame decoder ([crate::decoder::SpecDecodeSession]) onto the packet-to-frame trait surface.

tile_list

§5.12 tile-list OBU + §7.3 large-scale-tile decoding.

Enums

Error

Crate-local error type.

Functions

decode_av1

Decode an AV1 IVF v0 buffer into a vector of decoded decoder::Frames.

decode_av1_at_operating_point

r430 — decode_av1 at an externally selected operating point (§6.7.5 choose_operating_point()): with a non-zero OperatingPointIdc the §5.3.1 drop_obu() rule skips every OBU carrying an extension header outside the point’s temporal/spatial layer set, so a temporally scalable stream decodes to exactly the shown frames of the surviving layers. See decoder::decode_av1_at_operating_point.

encode_av1

Encode planar 4:2:0 8-bit YUV pixels into an intra-only AV1 elementary stream (IVF v0 container).

register

Codec registration entry point.