mirror of https://github.com/storytold/filmcraft.git synced 2026-10-29 20:47:00 -06:00

T

Brandon ThomasandClaude Opus 5.5 aefe1ae08f M2.4: H.264 CABAC entropy decoding

- arithmetic decoding engine (DecodeDecision / Bypass / Terminate, 9-bit
  register semantics incl. I_PCM re-initialisation), combined state
  transition table, round-trip tested against a reference encoder model
- context initialisation for cabac_init_idc 0..2 and I slices, all 1024
  (m, n) pairs extracted from Tables 9-12..9-33 of the spec
- binarisations + ctxIdxInc derivations: mb_skip_flag, mb_type (I/P/B incl.
  intra suffixes and I_PCM), sub_mb_type, ref_idx, mvd (UEG3), prev/rem intra
  modes, intra_chroma_pred_mode, coded_block_pattern, mb_qp_delta,
  transform_size_8x8_flag, coded_block_flag (all block categories incl.
  inferred 8x8 flags), significant/last (frame, 4x4 and 8x8 tables),
  coeff_abs_level_minus1 (UEG0), end_of_slice_flag

The full fixture matrix (32 libx264 configurations: Baseline/Main/High,
CABAC+B-pyramid, weightp/weightb, direct temporal/spatial, ref=4, deblock
variants, cqm=jvt, 4 slices, open GOP, constrained intra, 8x8dct=0, QP 1/50,
720p/1080p/1918x1078 crop) decodes bit-exact against ffmpeg.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-09-30 06:19:54 -04:00