daedalus-v4l2/daemon/src/shadow_decoder.c

/* SPDX-License-Identifier: BSD-2-Clause */
/*
 * shadow_decoder.c — env-gated parallel daedalus-decoder wiring.
 *
 * PR-Q3a.1 scope: prove the toolchain.
 *
 *   1. DAEDALUS_SHADOW_MODE=1 + libavcodec carries marfrit-packages
 *      0016 (ff_h264_set_mb_inspect_cb) → shadow path active.
 *   2. Per-MB callback fires on every macroblock libavcodec emits.
 *      We only count the firings here.
 *   3. Frame boundary creates a daedalus_decoder context lazily
 *      (sized from the first AVFrame); destroy + recreate on
 *      resolution change.
 *   4. Per-frame log line surfaces MB count + has_qpu state.
 *
 * No daedalus_decoder_append_mb / flush_frame calls yet — that
 * needs H264Context introspection which depends on the patched
 * FFmpeg source-tree headers (DAEDALUS_FFMPEG_SRC) and lands in
 * PR-Q3a.2.  This module's job here is to confirm the link
 * survives, the callback resolves, the context creates, and
 * tearing the path back down doesn't perturb the production
 * AVFrame → V4L2 pipeline.
 */
#include "shadow_decoder.h"

#include "ffmpeg_loader.h"
#include "log.h"

#include <libavcodec/avcodec.h>
#include <libavutil/frame.h>

#include <daedalus_decoder.h>

#include <stdlib.h>
#include <string.h>

struct shadow_decoder {
	struct ffmpeg_loader *loader;
	daedalus_decoder     *dec;	/* lazily created on first frame */
	int                   ctx_w;	/* coded-frame width at last create */
	int                   ctx_h;
	uint64_t              mbs_this_frame;
	uint64_t              total_frames;
	uint64_t              total_mbs;
};

static void shadow_mb_inspect(void *opaque,
			      const struct H264Context *h __attribute__((unused)),
			      int mb_x __attribute__((unused)),
			      int mb_y __attribute__((unused)))
{
	struct shadow_decoder *sh = opaque;
	sh->mbs_this_frame++;
}

struct shadow_decoder *shadow_decoder_create(struct ffmpeg_loader *loader)
{
	const char *env = getenv("DAEDALUS_SHADOW_MODE");

	if (!env || strcmp(env, "1") != 0)
		return NULL;

	if (!loader || !loader->ff_h264_set_mb_inspect_cb) {
		log_warn("shadow_decoder: DAEDALUS_SHADOW_MODE=1 set but "
			 "libavcodec lacks ff_h264_set_mb_inspect_cb — disabled");
		return NULL;
	}

	struct shadow_decoder *sh = calloc(1, sizeof(*sh));
	if (!sh) {
		log_err("shadow_decoder: out of memory");
		return NULL;
	}
	sh->loader = loader;
	log_info("shadow_decoder: enabled (DAEDALUS_SHADOW_MODE=1, "
		 "daedalus-decoder version %s)",
		 daedalus_decoder_version());
	return sh;
}

void shadow_decoder_destroy(struct shadow_decoder *sh)
{
	if (!sh)
		return;
	if (sh->dec)
		daedalus_decoder_destroy(sh->dec);
	log_info("shadow_decoder: shutdown — observed %llu frames / %llu MBs",
		 (unsigned long long) sh->total_frames,
		 (unsigned long long) sh->total_mbs);
	free(sh);
}

void shadow_decoder_install_cb(struct shadow_decoder *sh,
			       struct AVCodecContext *avctx)
{
	if (!sh || !avctx)
		return;
	/*
	 * Loader's optional-symbol pointer was checked at create time
	 * (we wouldn't be non-NULL otherwise), so the call is safe.
	 */
	sh->loader->ff_h264_set_mb_inspect_cb(avctx, shadow_mb_inspect, sh);
	log_info("shadow_decoder: per-MB callback installed on H.264 ctx");
}

/*
 * Ensure the daedalus_decoder context matches the frame's dimensions.
 * Rounds up to the H.264 macroblock grid (16-pixel multiples) — the
 * coded picture is always 16-aligned even when the displayed crop
 * isn't.  Returns 0 on success, -1 on failure (ctx left NULL; caller
 * logs and continues without shadow dispatch this frame).
 */
static int shadow_ensure_ctx(struct shadow_decoder *sh, int w, int h)
{
	int coded_w = (w + 15) & ~15;
	int coded_h = (h + 15) & ~15;

	if (sh->dec && sh->ctx_w == coded_w && sh->ctx_h == coded_h)
		return 0;

	if (sh->dec) {
		daedalus_decoder_destroy(sh->dec);
		sh->dec = NULL;
	}

	sh->dec = daedalus_decoder_create(coded_w, coded_h);
	if (!sh->dec) {
		log_warn("shadow_decoder: daedalus_decoder_create(%dx%d) "
			 "failed — shadow dispatch skipped this stream",
			 coded_w, coded_h);
		sh->ctx_w = sh->ctx_h = 0;
		return -1;
	}
	sh->ctx_w = coded_w;
	sh->ctx_h = coded_h;
	log_info("shadow_decoder: ctx ready (%dx%d coded, has_qpu=%d)",
		 coded_w, coded_h, daedalus_decoder_has_qpu(sh->dec));
	return 0;
}

void shadow_decoder_on_frame(struct shadow_decoder *sh,
			     const struct AVFrame *fr)
{
	if (!sh || !fr)
		return;

	(void) shadow_ensure_ctx(sh, fr->width, fr->height);

	sh->total_frames++;
	sh->total_mbs += sh->mbs_this_frame;

	uint64_t expected = (uint64_t) ((fr->width + 15) >> 4) *
			    (uint64_t) ((fr->height + 15) >> 4);
	log_info("shadow_decoder: frame #%llu %dx%d — %llu MBs observed "
		 "(expected %llu)",
		 (unsigned long long) sh->total_frames,
		 fr->width, fr->height,
		 (unsigned long long) sh->mbs_this_frame,
		 (unsigned long long) expected);

	sh->mbs_this_frame = 0;
}