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marfrit dcbbc77038 Path B pivot + Phase 0-3 closed with first baseline numbers

This is a from-scratch initial commit on a fresh .git. The original
scaffold commit (7510b56) and the earlier session's working-tree
docs were lost in a 2026-05-18 10:25 working-tree wipe; the corrupted
.git is preserved at .git-broken-2026-05-18/ (gitignored) for
forensic inspection.

Scope re-anchored from Path A (custom VPU firmware on VC7 scalar
cores; blocked by BCM2712 silicon-RoT mask-ROM signature check)
to Path B (QPU compute kernels via Mesa v3d / Vulkan compute or
direct DRM, on stock signed Pi 5 / CM5). See README.md and
docs/phase0.md for the substrate audit that closed Path A.

Phases closed:
  Phase 0 — substrate audit; Path A blocked, Path B open;
            codec-back-end-fits-QPU finding (docs/phase0.md)
  Phase 1 — first kernel locked (VP9 / AV1 8x8 inverse DCT) with
            publish-before-measure R = M2/M3 decision rules
            (docs/phase1.md)
  Phase 2 — reference impls mapped; FFmpeg n7.1.3 source vendored
            under external/ffmpeg-snapshot/ (PROVENANCE.md pins
            commit f46e514 + per-file SHA-256s) (docs/phase2.md)
  Phase 3 — real baseline measurements on hertz (docs/phase3.md):
              M1 bit-exact            100.0000 % (10000/10000)
              M3 NEON IDCT8 single    8.171 Mblock/s (122.4 ns/block)
              M5a empty Vulkan submit 22.66 us
              M5b 1-WG noop dispatch  55.60 us
              M5 delta                32.95 us/dispatch
            => per-dispatch overhead is ~455x per-NEON-block cost;
               Phase 4 must batch at frame level or close to it.

Build harness in place: CMakeLists.txt + tests/{bench_neon_idct.c,
vp9_idct8_ref.c, bench_vulkan_dispatch.c, shaders/noop.comp} +
external/ffmpeg-snapshot/config.h shim (7 defines + EXTERN_ASM).
Builds clean on Debian Trixie aarch64 with cmake 3.31, ninja 1.12,
libvulkan-dev 1.4.309, glslang-tools 15.1.0. Vendored FFmpeg .S
assembles via the config.h shim.

Next: Phase 4 (plan first QPU IDCT kernel under the M5 batching
constraint) -> Phase 5 second-model review -> Phase 6 implement.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-18 11:30:12 +00:00

3.7 KiB

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FFmpeg source snapshot

Verbatim subset of FFmpeg source pinned for use as reference implementations of the VP9 8×8 inverse DCT (Phase 1 target of daedalus-fourier). See ../../docs/phase2.md §2 and §5 for the rationale.

Upstream pin

Repository: https://github.com/FFmpeg/FFmpeg
Tag: n7.1.3 (matches libavcodec61 8:7.1.3-0+deb13u1+rpt1 shipping in Debian Trixie on the dev host hertz)
Annotated tag object: 0a9a757e96fdf053697084bbd1f620edeac9d084
Commit object (tag target): f46e514491172d15bd74b4abb1814cd2f05a763e
Snapshot fetched: 2026-05-18 (UTC), via https://raw.githubusercontent.com/FFmpeg/FFmpeg/n7.1.3/<path>

Files in this snapshot

All files are byte-for-byte copies of the upstream source at the tagged commit, no modifications.

Path	Lines	Bytes	SHA-256
`libavcodec/vp9dsp_template.c`	2578	89045	`41b21f667a6c497b620aa1637d8269badc45d1ac7e621d694441c5bf39356e4f`
`libavcodec/aarch64/vp9itxfm_neon.S`	1580	63534	`82ee3ceed4735c63576bafdcee28e2215652743ade55a9eab46a16d9530369f6`
`libavcodec/aarch64/neon.S`	173	7496	`72d36ce6c3fcc5e53de869cfe10fda16225ebe580c32891bccc240a30a85a538`
`libavutil/aarch64/asm.S`	260	8069	`c0d03143b1bc5a9e358222d08d2d449d595271844fe7a3dc23bffb91abe8b0e3`
`COPYING.LGPLv2.1`	502	—	`b634ab5640e258563c536e658cad87080553df6f34f62269a21d554844e58bfe`

Verify with:

( cd external/ffmpeg-snapshot && sha256sum -c <<'EOF'
41b21f667a6c497b620aa1637d8269badc45d1ac7e621d694441c5bf39356e4f  libavcodec/vp9dsp_template.c
82ee3ceed4735c63576bafdcee28e2215652743ade55a9eab46a16d9530369f6  libavcodec/aarch64/vp9itxfm_neon.S
72d36ce6c3fcc5e53de869cfe10fda16225ebe580c32891bccc240a30a85a538  libavcodec/aarch64/neon.S
c0d03143b1bc5a9e358222d08d2d449d595271844fe7a3dc23bffb91abe8b0e3  libavutil/aarch64/asm.S
b634ab5640e258563c536e658cad87080553df6f34f62269a21d554844e58bfe  COPYING.LGPLv2.1
EOF
)

License

LGPL-2.1-or-later. See COPYING.LGPLv2.1. Original copyright holders include the FFmpeg authors and Google Inc. (2016) for the aarch64 NEON paths. The snapshot inherits FFmpeg's license in full.

Why each file is in this snapshot

libavcodec/vp9dsp_template.c — contains idct_idct_8x8_add_c, the bit-exact C reference for the Phase 1 kernel under test (M1).
libavcodec/aarch64/vp9itxfm_neon.S — contains ff_vp9_idct_idct_8x8_add_neon, the NEON throughput baseline (M3). Also defines idct8, dmbutterfly0, dmbutterfly, dmbutterfly_l, butterfly_8h, and the idct_coeffs constant table.
libavcodec/aarch64/neon.S — defines transpose_8x8H used by vp9itxfm_neon.S.
libavutil/aarch64/asm.S — defines function, endfunc, movrel, const, endconst, and other assembly preamble macros required to assemble the above NEON files.

Re-vendoring procedure

If the upstream pin needs to change (e.g., hertz updates to a newer libavcodec):

TAG=nX.Y.Z
BASE=https://raw.githubusercontent.com/FFmpeg/FFmpeg/$TAG
cd external/ffmpeg-snapshot
for f in libavcodec/vp9dsp_template.c \
         libavcodec/aarch64/vp9itxfm_neon.S \
         libavcodec/aarch64/neon.S \
         libavutil/aarch64/asm.S \
         COPYING.LGPLv2.1; do
  curl -sSf -o "$f" "$BASE/$f"
done
sha256sum libavcodec/vp9dsp_template.c \
          libavcodec/aarch64/vp9itxfm_neon.S \
          libavcodec/aarch64/neon.S \
          libavutil/aarch64/asm.S \
          COPYING.LGPLv2.1
# update this PROVENANCE.md with the new tag, commit hash, and hashes

After re-vendoring, re-run the bit-exact gate (M1) and throughput baseline (M3) — both can shift across FFmpeg versions even when the VP9 spec doesn't change (e.g., NEON micro-optimizations).

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