claude-noether
1e9619afe8
V4L2 stateless AV1 passes the sequence header information as a structured control (V4L2_CID_STATELESS_AV1_SEQUENCE) and ships only tile-group bytes in the OUTPUT buffer. libavcodec's AV1 decoder is full-bitstream, so the daemon needs to reconstruct the OBU bytes the consumer parsed out before feeding the assembled stream to libavcodec. This commit lands the Sequence Header OBU half of that reconstruction — av1_synth_sequence_header_obu(). Frame Header / Frame OBU synthesisers + the integration that wires the assembled OBUs into the decode hot path are separate follow-on modules. Module shape mirrors the H.264 NAL synthesiser (PR #1): - Public API: single function returning byte count or 0 on overflow/invalid input. - Wire encoder uses the existing bitstream_writer (bsw_put_u is AV1's f(n); bsw_put_ue is bit-identical to AV1's uvlc; bsw_align_rbsp matches AV1's trailing_bits()). - AV1-specific helpers (leb128 size, min_bits_for, subsampling resolution per §5.5.2) are file-local statics. - No emulation prevention — AV1 uses leb128-sized OBUs for bitstream boundaries, not byte-pattern escapes. Synthesis decisions for fields V4L2 doesn't carry are documented verbatim in the file header (reduced_still_picture_header = 0; single operating point at seq_level_idx = 13 / level 5.1; color_description_present_flag = 0; chroma_sample_position = 0; seq_choose_screen_detection_tools = 1; seq_choose_integer_mv = 1). Rejection cases: - seq_profile > 2 - bit_depth not in {8, 10, 12} - seq_profile = 1 + monochrome (4:4:4 forced colour) - seq_profile = 1 + bit_depth = 12 (only profile 2 allows it) - max_frame_{width,height}_minus_1 requiring > 16 length bits - out_cap too small to hold header + leb128 + payload Each returns 0 to surface the mismatch loudly rather than emit nonsense the libavcodec parser would reject downstream. Unit test (test_av1_obu_synth.c, opt-in via DAEDALUS_BUILD_TESTS=ON) exercises four cases bit-by-bit against a hand-computed reference: 1. profile 0, 1080p, 8-bit, 4:2:0, order_hint on (7 bits), CDEF+restoration on — the common Pi 5 path. 2. profile 0, 720p, 10-bit, monochrome — exercises high_bitdepth and the monochrome short-form color_config. 3. profile 1 + bit_depth 12 → expects 0 (rejected). 4. tiny out_cap → expects 0 (overflow). All four green on hertz (aarch64 Arch, gcc Wall+Wextra+Wpedantic clean). This commit does not change daemon behaviour — av1_obu_synth.c is built into the daemon binary so the symbols are reachable, but no call site is wired yet. Integration goes in the follow-on DAEMON-AV1 patches that also synthesise the Frame Header OBU and bracket the assembled OBUs with a Temporal Delimiter. Refs reauktion/daedalus-v4l2#11 daemon-half; closes daedalus backlog task #144.
daedalus-v4l2
V4L2 stateless decoder for the Raspberry Pi 5 / CM5, backed by the
daedalus-fourier kernel library (VP9 + AV1 CDEF + H.264 video
decode kernels on VideoCore VII compute + ARM NEON).
Status: scaffold (2026-05-18). Architecture locked per daedalus-fourier session memory; implementation not yet begun.
What this is
Sibling repo to daedalus-fourier (the kernel library; cycles 1-9 closed).
A two-piece userspace + kernel-module stack that exposes a V4L2
stateless decoder interface (/dev/videoNN) so that
libva-v4l2-request-fourier → firefox-fourier /
chromium-fourier can drive it the same way they drive existing
hardware-decode pipelines on Pi 5 / RK3588.
+-----------------------------------------------------------+
| firefox-fourier / chromium-fourier (existing) |
+-----------------------------------------------------------+
| VA-API |
+-----------------------------------------------------------+
| libva-v4l2-request-fourier (existing, sibling project) |
+-----------------------------------------------------------+
| V4L2 stateless ioctl uAPI |
+-----------------------------------------------------------+
| daedalus-v4l2 kernel module (`kernel/`) |
| - registers /dev/videoNN |
| - parses V4L2 stateless ioctls (VP9/AV1/H.264 controls) |
| - forwards bitstream + controls to userspace daemon |
| via chardev or netlink |
+-----------------------------------------------------------+
| daedalus-v4l2 userspace daemon (`daemon/`) |
| - takes bitstream blobs + per-slice controls |
| - drives FFmpeg parsers via dlopen (Option γ) |
| - dispatches per-block ops via daedalus-fourier |
| public API (daedalus_dispatch_*) |
| - posts decoded frames back to kernel module |
+-----------------------------------------------------------+
| daedalus-fourier kernel library (sibling project) |
| - exports include/daedalus.h public API |
| - per-kernel CPU NEON + opportunistic V3D QPU dispatch |
| - 9 closed cycles across VP9, AV1 CDEF, H.264 |
+-----------------------------------------------------------+
| V3D 7.1 (Mesa userspace v3dv) + ARM NEON (BCM2712) |
+-----------------------------------------------------------+
Why this architecture (Option B + γ + sibling)
Locked by user 2026-05-18 from 3 options in
daedalus-fourier/docs/phase8_scoping.md:
- Option B over A (userspace v4l2loopback): real
/dev/videoNN, proper DRM PRIME / dmabuf for browser zero-copy. - Option γ: dlopen FFmpeg as parser at runtime. No vendoring, fastest to v1.
- Sibling repo: per
project_consumer_targetconvention, V4L2-side work lives outside daedalus-fourier so the kernel-library has a clean API boundary.
Status
Initial scaffold only. See docs/architecture.md for the
deeper design and docs/roadmap.md for the
sub-phase breakdown.
Repo layout
kernel/— Linux kernel module (V4L2 device registration + ioctl handling + userspace chardev bridge). Out-of-tree.daemon/— userspace decoder daemon (linkslibdaedalus_core.afrom sibling daedalus-fourier; uses dlopen for FFmpeg parser).include/— shared headers between kernel and daemon.docs/— architecture + roadmap.
License
Kernel module: GPLv2 (required for kernel-tree compatibility). Userspace daemon: BSD-2-Clause (matches daedalus-fourier).