Cycle 7 of the libavcodec.so substitution arc (reauktion/daedalus-v4l2#11
step 2). H264DSPContext.idct8_add — called per 8×8 block from the
High-profile intra-8×8-DCT decode path in libavcodec/h264_mb.c — now
dispatches through daedalus_recipe_dispatch_h264_idct8 instead of
ff_h264_idct8_add_neon.
## What
- Add 0004-h264-idct8-daedalus-fourier.patch (in both arch/ and debian/
ffmpeg-v4l2-request-fourier/). Extends libavcodec/aarch64/
h264_idct_daedalus.c (introduced by 0003) with ff_h264_idct8_add_daedalus
and a daedalus_recipe_dispatch_h264_idct8 call; patches
libavcodec/aarch64/h264dsp_init_aarch64.c to wire c->idct8_add to
the new shim.
- arch/PKGBUILD + debian/build-deb.sh: append the new patch to the
apply list; bump pkgrel/PKGREL to 7.
- No new build-deps, no Depends change, no daedalus-fourier rev — the
d87239d pin already exposes daedalus_recipe_dispatch_h264_idct8.
## Why
The recipe layer picks the substrate; for cycle 7 (H.264 IDCT 8×8)
the recipe is CPU NEON, so this is effectively a NEON-to-NEON
substitution layered on top of cycle 6. Production validation of
cycle 6 on higgs Firefox YouTube: 3040 frames decoded cleanly,
avg_decode_us=3388 (no regression vs the pre-substitution ~4 ms
baseline). Cycle 7 inherits the same shim's pthread_once context.
Bit-exact against ff_h264_idct8_add_neon (daedalus-fourier cycle 7
green; FFmpeg 8×8 block storage block[r + 8*c] matches daedalus
column-major convention).
## Scope NOT covered (deferred)
- Bulk c->idct8_add4 (inter 8×8-DCT macroblocks) stays on the
in-tree NEON .S code; batched substitution with n_blocks>1 lands
later alongside the cycle-6 bulk-paths work.
- High-bit-depth (10-bit) path untouched.
- Cycles 8/9 — separate PRs.
## SONAME
Unchanged. libavcodec.so.62 / libavformat.so.62 / libavutil.so.60.
## Refs
- reauktion/daedalus-v4l2 issue #11 (substitution arc): reauktion/daedalus-v4l2#11
- marfrit-packages PR #76 (cycle 6 IDCT 4×4)
- marfrit-packages PR #78 (libxml2 ABI-skew workaround)
- marfrit/daedalus-fourier cycle 7 close (H.264 IDCT 8×8 NEON green)
