oxideav-evc

Pure-Rust EVC — MPEG-5 Essential Video Coding (ISO/IEC 23094-1) video decoder. Baseline + Main profiles. Zero C dependencies, zero FFI, zero *-sys.

Part of the oxideav framework but usable standalone.

Round-7 status

Working Baseline-profile decoder for IDR + P + B slices with full residual coding, luma + chroma deblocking, and the 64-point IDCT, plus the Main-profile CABAC initialization tables (Tables 40-90) and the §9.3.4.2 ctxInc derivation helpers. Decode of the Main-profile syntax elements themselves remains parked behind Error::Unsupported — the round-7 deliverable lands the CABAC infrastructure so subsequent rounds can implement individual tools without revisiting initValue churn.

The remaining Baseline constraints (future rounds will lift them):

• 8-bit luma + chroma (4:2:0).
• sps_addb_flag = 0 (deblocking uses the §8.8.2 baseline filter; the Main-profile advanced deblocking §8.8.3 is parked).
• Single reference picture per list (num_ref_idx_active_minus1_l? = 0).
• Sub-pel MV phases restricted to the Baseline 1/4-pel grid for luma (Table 25 phases 4, 8, 12) and 1/8-pel grid for chroma (Table 27 phases 4, 8, 12, 16, 20, 24, 28).

Anything outside the Baseline toolset (BTT, SUCO, ADMVP, EIPD, IBC, ATS, ADCC, ALF, DRA, AMVR, MMVD, affine, DMVR, HMVP, …) bubbles up as Error::Unsupported — but the CABAC contexts are now ready.

Round-7 deltas vs round 6

• Main-profile CABAC init tables: every initValue from ISO/IEC 23094-1 §9.3.5 Tables 40-90 (BTT split, SUCO, cu_skip, AMVR, MMVD, affine, ALF, DRA, ATS, ADCC, IBC, mvp_idx, merge_idx, ref_idx, abs_mvd, intra_pred_mode + MPM, inter_pred_idc, cbf_all/luma/cb/cr, cu_qp_delta_abs, sig_coeff_flag, coeff_abs_level_greaterA/B, last_sig_coeff_x/y_prefix, …) lives in the new cabac_init module as pub const arrays keyed by the [MainCtxTable] enum (discriminant = spec table number).
• §9.3.2.2 init pipeline (eq. 1425/1426) wired through init_main_profile_contexts, which walks every Main-profile table and installs the per-(table, ctxIdx) (valState, valMps) derived from the slice QP. Table 39's initType=0 (I) vs initType=1 (P/B) split is encoded in [MainCtxTable::init_type_range].
• §9.3.4.2.2-12 ctxInc helpers: pure-function ports of the per-syntax-element ctxInc derivations for coeff_zero_run / coeff_abs_level_minus1, split_unit_coding_order_flag, the neighbour-block sum used by affine_flag / cu_skip_flag / pred_mode_flag / ibc_flag, btt_split_flag (with Table 97 ctxSetIdx), last_sig_coeff_{x,y}_prefix, sig_coeff_flag, coeff_abs_level_greaterA/B_flag, coeff_abs_level_remaining Rice-parameter (Table 98), ats_cu_inter_flag, and ats_cu_inter_horizontal_flag.

Round-6 deltas vs round 5

• Chroma deblocking: §8.8.2 chroma path per eq. 1167-1213. The 2-tap stencil (only sB and sC mutate — eq. 1208/1209/1212/1213) runs against both Cb and Cr planes after the luma pass. Table 33 is keyed by qp_c = Clip3(0, 51, slice_qp + slice_cb_qp_offset) for Cb (with slice_cr_qp_offset for Cr — eq. 1194). Edge spacing scales via Table 2 sub-sampling factors (4:2:0 → every 2 chroma samples).

Round-5 deltas vs round 4

• Residual coding: residual_coding_rle() per §7.3.8.7 now drives per-position TransCoeffLevel reconstruction. Each non-zero CBF triggers the dequant + inverse-transform + add-to-predictor pipeline (intra and inter both supported).
• 64×64 IDCT: the spec's eq. 1071-1076 has m/n indexing typos that blocked transcription in round 3. Round 5 builds the matrix from the closed form M[m][n] = round(64·√2·cos(π·m·(2n+1)/128)) for m≥1 (M[0][n] = 64), verified against every printed entry of eq. 1072 / eq. 1074.
• Deblocking: §8.8.2 luma path with the BS table from Table 33, the 4-tap edge filter from eq. 1148-1158, and per-4×4-grid side-info tracking (PredMode + CBF + MV + RefIdx) populated as CUs decode.

167 unit tests cover the CABAC engine, NAL / parameter-set parsing, the slice_data() walker, the IDR pixel pipeline, the inter-prediction primitives, the residual / dequant / IDCT chain, the 64-point IDCT construction, the deblocking filter math for both luma (4-tap) and chroma (2-tap) — Table 33 spot checks, BS rules, edge smoothing fixtures, the chroma_qp_offset switch, the end-to-end no-op pass on a uniform-grey IDR — and the round-7 Main-profile CABAC infrastructure (Tables 40-90 spot checks, Table 39 init-type ranges, the §9.3.4.2.x ctxInc helpers, and end-to-end init_main_profile_contexts derivation at QP 22 / 32).