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daemon: shadow_decoder wiring (PR-Q3a.1) #25

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marfrit merged 1 commits from noether/daemon-shadow-decoder-wiring into main 2026-05-26 12:28:17 +00:00
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marfrit commented 2026-05-26 12:15:37 +00:00
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Toolchain plumbing for the upcoming daedalus-decoder shadow-mode path. Production behaviour is unchanged.

What lands here

  1. CMake links libdaedalus_decoder.a via pkg-config (depends on the daedalus-decoder.pc shipped by daedalus-decoder#17, merged today). Static archive — 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-h264-mb-inspect-callback.patch exports it. Shadow path activates only when both env DAEDALUS_SHADOW_MODE=1 AND the symbol resolves.
  3. New shadow_decoder.[ch]:
    • 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; a lazily-created daedalus_decoder context picks up dimensions from the first observed 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.

What stays out

PR-Q3a.1 scope ENDS at the callback counting 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 (architectural)

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, no new .so dependencies.
  • Disabled state (env unset OR symbol absent): no shadow log lines, daemon init continues normally. Startup logs libavcodec lacks ff_h264_set_mb_inspect_cb (stock build, no daedalus-fourier 0016 patch) — shadow-mode unavailable.
  • Enabled state: requires ffmpeg-v4l2-request-fourier rebuilt with patches 0016/0017 and deployed to hertz. Currently-installed release 10 predates them. Deployment task, separate from this PR.

Followups

  • Build + deploy fresh ffmpeg-v4l2-request-fourier .deb (release 11+) carrying patches 0016/0017 so the enabled-state shadow path is exercised on hertz.
  • PR-Q3a.2: transcribe the CLI's real-coeffs + edge-derivation path into shadow_decoder.c (gated on DAEDALUS_FFMPEG_SRC).
Toolchain plumbing for the upcoming daedalus-decoder shadow-mode path. Production behaviour is unchanged. ## What lands here 1. **CMake** links `libdaedalus_decoder.a` via pkg-config (depends on the `daedalus-decoder.pc` shipped by [daedalus-decoder#17](https://git.reauktion.de/marfrit/daedalus-decoder/pulls/17), merged today). Static archive — 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-h264-mb-inspect-callback.patch` exports it. Shadow path activates only when both env `DAEDALUS_SHADOW_MODE=1` AND the symbol resolves. 3. **New `shadow_decoder.[ch]`**: - `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`; a lazily-created `daedalus_decoder` context picks up dimensions from the first observed `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`. ## What stays out PR-Q3a.1 scope ENDS at the callback counting 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 (architectural) 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, no new .so dependencies. - **Disabled state (env unset OR symbol absent)**: no shadow log lines, daemon init continues normally. Startup logs `libavcodec lacks ff_h264_set_mb_inspect_cb (stock build, no daedalus-fourier 0016 patch) — shadow-mode unavailable`. - **Enabled state**: requires `ffmpeg-v4l2-request-fourier` rebuilt with patches 0016/0017 and deployed to hertz. Currently-installed release 10 predates them. Deployment task, separate from this PR. ## Followups - Build + deploy fresh `ffmpeg-v4l2-request-fourier` .deb (release 11+) carrying patches 0016/0017 so the enabled-state shadow path is exercised on hertz. - **PR-Q3a.2**: transcribe the CLI's real-coeffs + edge-derivation path into `shadow_decoder.c` (gated on `DAEDALUS_FFMPEG_SRC`).
marfrit added 1 commit 2026-05-26 12:15:37 +00:00
daemon: shadow_decoder wiring (PR-Q3a.1) dbf01eddb8 
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 merged commit 6b1d90816d into main 2026-05-26 12:28:17 +00:00
marfrit deleted branch noether/daemon-shadow-decoder-wiring 2026-05-26 12:28:17 +00:00
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Reference: reauktion/daedalus-v4l2#25
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