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claude-noether 1e9619afe8 daemon: AV1 Sequence Header OBU synthesiser + unit test

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.

2026-05-23 15:41:07 +02:00

src

daemon: AV1 Sequence Header OBU synthesiser + unit test

2026-05-23 15:41:07 +02:00

CMakeLists.txt

daemon: AV1 Sequence Header OBU synthesiser + unit test

2026-05-23 15:41:07 +02:00

README.md

Initial scaffold: daedalus-v4l2 sibling repo

2026-05-18 14:54:56 +00:00

README.md

daemon/ — daedalus-v4l2 userspace decoder daemon

Userspace daemon that:

Connects to the kernel module's chardev
Receives bitstream + V4L2 control blobs
Parses bitstream via dlopen'd FFmpeg
Dispatches per-block work via daedalus_dispatch_* from sibling daedalus-fourier
Returns decoded frames to kernel

Status

Scaffold only. Phase 8.3 not yet started.

Build dependencies (planned)

libdaedalus_core.a from sibling daedalus-fourier (static link)
FFmpeg dev headers (for AVPacket/AVCodec interface types) + runtime FFmpeg .so (loaded via dlopen)
libv4l2 (for V4L2 control struct definitions)
pthread

Build (when implemented)

mkdir build && cd build
cmake .. -DDAEDALUS_FOURIER_DIR=/path/to/daedalus-fourier
make

Layout (planned)

CMakeLists.txt
src/main.c — event loop, chardev connection
src/parser.c — FFmpeg dlopen wrapper + per-codec dispatch
src/decode_vp9.c, src/decode_av1.c, src/decode_h264.c — per-codec block walkers
src/frame_io.c — frame allocation, return to kernel

License

BSD-2-Clause (matches daedalus-fourier sibling).

Phase 8.3 starting point

A standalone program that:

Opens a .ivf or .mp4
Pulls codec packets via dlopen'd avformat
Calls dlopen'd avcodec to parse (without decoding)
Walks the block-level metadata
Validates output structure

No kernel involvement yet — just confirm the parse path works.