claude-noether
4182b32adf
User question 2026-05-23: 'Wayland does need a conversion of NV12 to
its output format. Could we cram that in?'
Yes — trivially. Added Stage 5 to the pipeline doc with:
- 5-line per-pixel compute shader (BT.709 limited-range example
given; matrix selected from H.264 VUI at runtime)
- explicit OPT-IN flag, off by default
- rationale for default-off: most consumers (V4L2 stateless,
Wayland zwp_linux_dmabuf NV12 passthrough, Firefox/mpv VAAPI
paths) want NV12 because compositors convert during composition
essentially for free. RGBA8 is 4x the bandwidth of NV12 — not
worth burning DMA + electrons when no downstream needs it
- colourspace metadata plumbing requirement: SPS vui_parameters
(colour_primaries, transfer_characteristics, matrix_coefficients,
video_full_range_flag) MUST flow through to the shader; default
BT.709 limited-range with warning if VUI absent
Updated the new-shader inventory to include v3d_h264_yuv_to_rgba.
Total dispatches/frame remains ~190-200; Stage 5 adds one.
daedalus-decoder
Frame-level GPU H.264 decoder for Raspberry Pi 5 / V3D7. Design phase — not implemented yet.
The objective: build the NVDEC-equivalent shape on Pi 5. One Vulkan submit per frame, one fence wait per frame, encoded H.264 bitstream in, NV12 frame out. Reuses daedalus-fourier's V3D compute primitives at the right granularity — not the per-block-call granularity that the kernel-substitution prototype exposed as architecturally wrong.
Sibling projects:
- daedalus-fourier — V3D + NEON kernel pack (IDCT, MC, deblock primitives). Stays as research/microbench artifact.
- daedalus-v4l2 — V4L2 stateless decoder shim + userspace daemon for Pi 5. The eventual consumer of this decoder.
- libva-v4l2-request-fourier — VAAPI ↔ V4L2 stateless bridge. End consumer.
See DESIGN.md for the architecture sketch.