Files

T

marfrit 5c8b09349c Cycle 9 closed: H.264 luma qpel mc20 = 131 Mblock/s NEON, CPU-only

Last unmeasured H.264 kernel. mc20 picked as representative
(horizontal half-pel, 6-tap filter; canonical for the H.264 luma
qpel family). M1 PASS 10000/10000 first try, M3 = 131.477
Mblock/s on a single core (7.6 ns/block), 135x the 1080p30 floor.

Per the cycles 6+7 lightweight-kernel rationale, Phase 4 deferred:
QPU dispatch floor (~250 ns/block) is 33x above the NEON per-block
cost; R9 ≈ 0.03 deep RED. No realistic QPU offload value.

Generalization: all H.264 luma MC variants (mc02, mc11, mc22,
etc.) will share this verdict. No need to measure each variant
individually.

H.264 NEON is dramatically faster than VP9 NEON across the board:
- IDCT 4x4: 175 vs N/A    (no VP9 analog)
- IDCT 8x8: 151 vs 8.2 Mblock/s (18x faster)
- MC 6/8-tap: 131 vs 7.0   (19x faster)
- Deblock: 92 vs 48 Medge/s (2x faster)

H.264 deployment recipe: all CPU NEON except deblock (opportunistic
QPU). On a Pi 5 running H.264-only, the QPU is mostly idle.

Cycles 1-9 complete. Public API exposes all 9.
Next: daedalus-v4l2 sibling repo per locked Phase 8 architecture
(B + γ + sibling), then README polish.

- external/ffmpeg-snapshot/libavcodec/aarch64/h264qpel_neon.S
  vendored (1467 lines, all qpel variants)
- tests/h264_qpel8_mc20_ref.c: 40-line C ref (clip255 of
  6-tap convolution)
- tests/bench_neon_h264qpel_mc20.c: M1 + M3 bench
- docs/k9_h264qpel_mc20.md: cycle 9 closure with comparison
  matrix

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

2026-05-18 14:53:21 +00:00

4.7 KiB

Raw Blame History

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/vp9lpf_neon.S`	1334	—	`384e49e7a6e838d9e38aedc00838ed4aebfa6c5bdb343ecaf23ef639bc10fbb7`
`libavcodec/aarch64/vp9mc_neon.S`	665	—	`6b1d50f9821742584fdd47758057f810644aff3a008faaa774ff5b9cac4d1fef`
`libavcodec/aarch64/h264idct_neon.S`	415	16269	`963ffe5f31b5a6a422e13b0d394cf5630126927abfb23aa214f7cbe83d60683f` — H.264 IDCT 4×4/8×8/DC NEON kernels for cycle 6+
`libavcodec/aarch64/h264dsp_neon.S`	1076	—	`978e076f0020e688b40c6dd827708c3d53e17c64a99fd0052e43d983536ce638` — H.264 in-loop deblock + weight/biweight kernels for cycle 8+
`libavcodec/aarch64/h264qpel_neon.S`	1467	—	`897b79be7856341847ad7a5ce6ca0c15a7acc439a95bf33ddab616cfe982c544` — H.264 luma qpel MC (16 mc-position variants × put/avg × 8x8/16x16) for cycle 9
`libavcodec/vp9_subpel_filters_table.c`	—	—	hand-extracted from `libavcodec/vp9dsp.c` at same n7.1.3 pin — provides `ff_vp9_subpel_filters` for `vp9mc_neon.S` to link against without dragging in vp9dsp.c's full init machinery
`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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