flush_frame now performs a real GPU dispatch via the daedalus-fourier
public API at frame batch granularity, in contrast to the substitution-
arc shim that paid Vulkan sync overhead per-block.
What's wired:
- Build per-frame luma-4x4 meta[] in raster order across all MBs
(N_MBs × 16 entries; 130,560 for 1080p)
- Repack per-MB coeffs[] (384 int16; first 256 are luma) into a flat
block-major coeffs buffer (n_blocks × 16 int16)
- Allocate a frame-sized scratch Y plane, zero-initialised — no intra
prediction yet so "predicted" = 0
- daedalus_recipe_dispatch_h264_idct4(ctx, scratch_y, stride, coeffs,
n_blocks, meta) — ONE call, ONE vkQueueSubmit, ONE vkQueueWaitIdle
- Copy result to caller's out_y at requested stride
Measured on hertz (Pi 5 / V3D 7.1 / daedalus-fourier 0.1.0 post-pool):
$ time ./build/test_smoke
daedalus-decoder version: 0.0.1
ctx created: 1920x1088, has_qpu=1
appended 8160 MBs (120x68)
flush_frame rc=0
Y non-zero bytes: 0 / 2088960
UV non-128 bytes: 0 / 1044480
smoke OK
real 0m0.163s
163ms wall for full 1080p frame including ctx-create (Vulkan init).
Per-block dispatch via the substitution arc would have paid
130,560 × ~50us = ~6.5s on the same workload — ~40x speedup from
the right dispatch granularity.
Smoke validates:
- flush_frame succeeds (rc=0) on a complete frame
- Zero-coefficient input → zero-pixel Y output (clip255(IDCT(zeros))=0)
- UV plane filled with neutral grey 128 (placeholder until chroma
dispatch lands)
What's deliberately deferred to follow-on sub-PRs:
- Intra prediction wavefront (Stage 2a) — predicted=0 means output
pixels are residual-only, not a valid frame decode. Sufficient for
Vulkan round-trip validation; not bit-exact vs FFmpeg yet.
- Motion compensation (Stage 2b) for inter MBs
- High-profile IDCT 8x8 (Stage 1 extension)
- Deblocking filter (Stage 4)
- Chroma 4x4 IDCT — needs separate dispatch with chroma stride
- Z-scan permutation of per-MB 4x4 block order (currently flat
raster; FFmpeg's per-MB coeffs[] uses spec §6.4.3 z-scan).
Bit-exact against FFmpeg requires this permutation; deferred to
the test-vector PR.
- dmabuf export (still memcpy-out)
- Stage 5 RGBA opt-in
API surface unchanged from the scaffold PR; only the body of
flush_frame becomes non-stub. Internal helpers stay file-local.
Stacks on noether/repo-scaffold (PR #2). Rebase on main after #2
lands; the diff is purely additive against the scaffold.
claude-noether