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ffmpeg-v4l2-request-fourier: route H.264 chroma DC Hadamard through daedalus-fourier (0011)

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Substitutes H264DSPContext.chroma_dc_dequant_idct in the 4:2:0 /
bit_depth=8 init path with a wrapper that composes the daedalus
chroma DC Hadamard primitive (daedalus-fourier PR #25) with the
qmul scaling FFmpeg's reference does in one fused function
(h264idct_template.c::ff_h264_chroma_dc_dequant_idct).

Algorithm per H.264 §8.5.11.1 / §8.5.11.2:
  1. Extract 4 DCs from the scattered positions in the per-MB
     coefficient buffer (stride=32, xStride=16)
  2. 2x2 Hadamard transform (daedalus primitive)
  3. qmul scale + >> 7, write back to original positions

Bit-exact against ff_h264_chroma_dc_dequant_idct_8_c. The Hadamard
itself is gated by the fourier PR #23 7-case test suite (including
the H·H = 4·I algebraic invariant), and the public-API parity
test added in PR #25 confirms the src/ symbol matches the test ref.

4:2:2 chroma stays on the in-tree ff_h264_chroma422_dc_dequant_idct_c
path — same chroma_format_idc<=1 gating shape as 0009 chroma deblock.

Pin bump: _daedalus_fourier_commit / DAEDALUS_FOURIER_COMMIT bumped
to b9f9ff2a (post-PR #25) so the build picks up the public
daedalus_h264_chroma_dc_hadamard_2x2 symbol.

Verified the patch applies cleanly on top of 0001-0010 against the
pinned upstream commit b57fbbe5 on hertz.
This commit is contained in:
Claude (noether)
2026-05-25 13:39:54 +02:00
parent 1f58ff2b6b
commit d8aa3aae8d
4 changed files with 209 additions and 4 deletions
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debian/ffmpeg-v4l2-request-fourier/build-deb.sh
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+2 -1
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@@ -45,7 +45,7 @@ PKGREL=10 # pkgrel=10 — H.264 luma qpel mc20 daedalus-fourier substitution
# DAEDALUS_KERNEL_H264_QPEL_MC20. Cycle 9 plumbs the last H.264 NEON
# kernel through the recipe layer. Daemon-side build (debian/daedalus-v4l2)
# can bump in a follow-up; this PR only changes the libavcodec.so consumer.
DAEDALUS_FOURIER_COMMIT=209a4218bcb98b91c04f07ad61513bb04adb13ad
DAEDALUS_FOURIER_COMMIT=b9f9ff2a89c068aea54dcb52b543afddad28311e # PR #25 — public chroma DC Hadamard
HERE=$(dirname "$(readlink -f "$0")")
@@ -77,6 +77,7 @@ patch -Np1 -i "$HERE/0007-h264-qpel-mc20-daedalus-fourier.patch"
patch -Np1 -i "$HERE/0008-h264-deblock-luma-h-daedalus-fourier.patch"
patch -Np1 -i "$HERE/0009-h264-deblock-chroma-daedalus-fourier.patch"
patch -Np1 -i "$HERE/0010-h264-deblock-luma-intra-daedalus-fourier.patch"
patch -Np1 -i "$HERE/0011-h264-chroma-dc-hadamard-daedalus-fourier.patch"
# --- daedalus-fourier: fetch + build static .a with PIC, install to a
# per-build prefix; libavcodec.so links it into the shared object so