Toolchain plumbing for the upcoming daedalus-decoder shadow-mode
path. Production behaviour is unchanged.
What lands here:
1. CMake links libdaedalus_decoder via pkg-config. Static archive,
so no .so dependency change in the daemon's link map.
2. ffmpeg_loader resolves ff_h264_set_mb_inspect_cb NULL-tolerantly.
Stock libavcodec lacks the symbol (logged as INFO at startup);
the marfrit-packages ffmpeg-v4l2-request-fourier fork's 0016
patch exports it. The shadow path activates only when both
env DAEDALUS_SHADOW_MODE=1 AND the symbol resolves.
3. New shadow_decoder.[ch] module:
- shadow_decoder_create() gates on env + symbol presence,
returns NULL in production state (the common case).
- shadow_decoder_install_cb() registers a per-MB callback on
the H.264 AVCodecContext; lazily-created daedalus_decoder
context will pick up dimensions from the first AVFrame.
- shadow_decoder_on_frame() logs per-frame MB-observed count.
Every entry point is NULL-safe so decoder.c stays clean of
conditionals.
4. decoder.{c,h} grow a `struct shadow_decoder *shadow` field on
daedalus_decoder. Install hook fires once per H.264 codec open;
frame hook fires after each successful avcodec_receive_frame.
PR-Q3a.1 scope ENDS here. The callback just counts MBs; no
daedalus_decoder_append_mb or flush_frame yet. Real-coeffs / edges
extraction needs the patched FFmpeg source-tree headers
(DAEDALUS_FFMPEG_SRC) to introspect H264Context internals — that
lands in PR-Q3a.2.
dejavu-check: this path is daedalus-decoder's frame-major UMA
dispatch architecture (one cmdbuf per frame, one submit) running
alongside libavcodec's reference decode for validation. It is NOT
per-kernel libavcodec function-pointer substitution. No new
libavcodec patches; the existing 0016 callback is the only intercept
point.
Verified on hertz:
- Build: clean, libdaedalus_decoder.a linked.
- Disabled state (env unset OR symbol absent): no shadow log
lines, daemon init continues normally, INFO logs
"libavcodec lacks ff_h264_set_mb_inspect_cb (stock build,
no daedalus-fourier 0016 patch) — shadow-mode unavailable".
- Enabled state would require ffmpeg-v4l2-request-fourier .deb
rebuilt with patches 0016/0017 deployed to hertz (current .deb
release 10 predates them). That's a deployment task, separate
from this PR.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
marfrit