ffmpeg-v4l2-request-fourier: substitute H.264 qpel mc20 → daedalus-fourier

H264QpelContext.put_h264_qpel_pixels_tab[1][2] (8x8 luma horizontal
half-pel, 6-tap "put" — the canonical representative of the H.264
luma motion-compensation family) now dispatches through
daedalus_recipe_dispatch_h264_qpel_mc20 instead of
ff_put_h264_qpel8_mc20_neon.

Cycle 9 of the daedalus-v4l2#11 step 2 substitution arc; closes the
4-cycle libavcodec.so substitution sequence:

  cycle 6 (PR #76)  H.264 IDCT 4x4         done
  cycle 7 (PR #85)  H.264 IDCT 8x8         done
  cycle 8 (PR #86)  H.264 luma-v deblock   done
  cycle 9 (this)    H.264 qpel mc20

Bumps daedalus-fourier pin d87239d → 209a421 (PR #2 — public API
gains daedalus_recipe_dispatch_h264_qpel_mc20 +
DAEDALUS_KERNEL_H264_QPEL_MC20).

Verdict per docs/k9_h264qpel_mc20.md: CPU NEON.  Per-block 7.6 ns at
131 Mblock/s gives 135× margin over 30 fps 1080p; QPU dispatch floor
at ~250 ns makes any V3D shader strictly worse.  Substitution is
plumbing-only — same daedalus_ctx_create_no_qpu pthread_once shape
the cycles 6/7/8 shims already own (kept SEPARATE from the H264DSP
shim's ctx because H264QPEL is its own libavcodec Makefile module
and link order does not guarantee a single .o owns the ctx symbol;
one extra ~µs init per process, paid lazily on first MC call).

Other H.264 luma MC variants (mc02, mc11, mc22 etc.) and the 16x16
size tier stay on the in-tree NEON .S code per the cycle-9 phase-1
rationale (mc20 8x8 is representative; remaining variants would
multiply recipe-lookup overhead without changing the substrate
verdict).

Bit-exact against ff_put_h264_qpel8_mc20_neon (daedalus-fourier
cycle 9 green; 10000/10000 random blocks bit-exact, M3 = 131 Mblock/s).

No SONAME change, no Depends change.  PKGREL 9 → 10.

Refs reauktion/daedalus-v4l2#11 — substitution arc step 2 cycle 9.

debian/ffmpeg-v4l2-request-fourier/build-deb.sh

@@ -33,18 +33,19 @@ FFMPEG_VERSION=8.1
 # epoch 2 matches Debian's stock ffmpeg (currently 7:7.1.x in trixie);
 # +rfourier suffix to avoid colliding with upstream/Debian rebuilds.
 PKGVER=2:${FFMPEG_VERSION}+rfourier+gb57fbbe
-PKGREL=9  # pkgrel=9 — restore AV_CODEC_FLAG_LOW_DELAY semantics in the
-          # H.264 decoder (FFmpeg 8.x dropped them).  Fixes the 2-1-4-3
-          # B-frame pair-swap that re-appeared in Firefox YouTube after
-          # the SONAME 61→62 jump (PR #75) silently neutered the
-          # daemon's ctx->flags |= AV_CODEC_FLAG_LOW_DELAY at
-          # daemon/src/decoder.c:202.  Substitution arc unchanged.
-          # (2026-05-22)
+PKGREL=10  # pkgrel=10 — H.264 luma qpel mc20 daedalus-fourier substitution
+           # (cycle 9 of the daedalus-v4l2#11 step 2 substitution arc; closes
+           # the libavcodec.so substitution sequence 6 IDCT4 / 7 IDCT8 /
+           # 8 luma-v deblock / 9 qpel mc20).  Pulls daedalus-fourier PR #2
+           # which extends the public API with
+           # daedalus_recipe_dispatch_h264_qpel_mc20.  (2026-05-23)
 
-# daedalus-fourier pin — first kernel substitution in libavcodec (cycle 6
-# H.264 IDCT 4x4).  Same SHA as the daedalus-v4l2 daemon already ships
-# inline; rev in lockstep with the daemon when the public API rolls.
-DAEDALUS_FOURIER_COMMIT=d87239d8172307d9a1b93c95cbed116d175b85cc
+# daedalus-fourier pin.  209a421 = daedalus-fourier PR #2 merge — public
+# API now exposes daedalus_recipe_dispatch_h264_qpel_mc20 +
+# 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
 
 HERE=$(dirname "$(readlink -f "$0")")
 
@@ -72,6 +73,7 @@ patch -Np1 -i "$HERE/0003-h264-idct4-daedalus-fourier.patch"
 patch -Np1 -i "$HERE/0004-h264-idct8-daedalus-fourier.patch"
 patch -Np1 -i "$HERE/0005-h264-deblock-luma-v-daedalus-fourier.patch"
 patch -Np1 -i "$HERE/0006-h264-restore-low-delay.patch"
+patch -Np1 -i "$HERE/0007-h264-qpel-mc20-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