feat(pipeline): resolve bundled ffmpeg fallback; integration test runs on real forest base

- run.py: add resolve_ffmpeg() mirroring setup_scales_media.py; change
  process_clip ff param to None and resolve at call time
- test_pipeline_integration.py: gate on resolve_ffmpeg() not PATH ffmpeg;
  verify proxy dims with cv2 instead of ffprobe
- ffmpeg_ops.py: add fps= to trim segments in crossfade_loop_args so xfade
  receives CFR input (xfade rejects 1/0 rate from raw trim output)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tools/pipeline/ffmpeg_ops.py

@@ -31,17 +31,20 @@ def frame_args(src, dst, *, start: float, duration: float,
 
 
 def crossfade_loop_args(src, dst, *, duration: float, overlap: float,
-                        ff: str = "ffmpeg") -> list[str]:
+                        fps: int = 30, ff: str = "ffmpeg") -> list[str]:
     """Stage 3 — make `src` loop seamlessly by crossfading its tail over its head.
     Output length = duration − overlap. Requires overlap < duration/2 so a non-empty
-    middle remains."""
+    middle remains.
+
+    fps is applied after each trim so xfade receives a constant-frame-rate stream
+    (xfade requires CFR; a raw trim output reports rate 1/0 which xfade rejects)."""
     if overlap <= 0 or overlap >= duration / 2:
         raise ValueError(f"overlap {overlap} must be in (0, duration/2={duration/2})")
     d, o = duration, overlap
     fc = (
-        f"[0:v]trim=0:{o},setpts=PTS-STARTPTS[head];"
-        f"[0:v]trim={o}:{d - o},setpts=PTS-STARTPTS[mid];"
-        f"[0:v]trim={d - o}:{d},setpts=PTS-STARTPTS[tail];"
+        f"[0:v]trim=0:{o},setpts=PTS-STARTPTS,fps={fps}[head];"
+        f"[0:v]trim={o}:{d - o},setpts=PTS-STARTPTS,fps={fps}[mid];"
+        f"[0:v]trim={d - o}:{d},setpts=PTS-STARTPTS,fps={fps}[tail];"
         f"[tail][head]xfade=transition=fade:duration={o}:offset=0[xf];"
         f"[xf][mid]concat=n=2:v=1,format=yuv420p[out]"
     )

tools/pipeline/run.py

@@ -4,6 +4,7 @@ this glue is covered by the opt-in integration test."""
 
 from __future__ import annotations
 
+import shutil
 import subprocess
 from pathlib import Path
 
@@ -12,6 +13,15 @@ from .ffmpeg_ops import crossfade_loop_args, frame_args, transcode_args
 MASTER_MAX_W = 3840
 
 
+def resolve_ffmpeg() -> str:
+    """ffmpeg from PATH, else the bundled imageio-ffmpeg binary (matches
+    simulator/setup_scales_media.py). The Pi/dev box may lack a system ffmpeg."""
+    if shutil.which("ffmpeg"):
+        return "ffmpeg"
+    import imageio_ffmpeg
+    return imageio_ffmpeg.get_ffmpeg_exe()
+
+
 def probe_duration(src, *, ff: str = "ffprobe") -> float:
     out = subprocess.run(
         [ff, "-v", "quiet", "-show_entries", "format=duration",
@@ -27,9 +37,10 @@ def _run(args: list[str]) -> None:
 
 def process_clip(src, out_dir, *, start: float = 0.0, duration: float | None = None,
                  overlap: float = 1.0, master_w: int = 3840, master_h: int = 2160,
-                 ff: str = "ffmpeg") -> dict:
+                 ff: str | None = None) -> dict:
     """Run stages 2–4 for one clip; return {'master','proxy','loop','mezzanine'} paths.
     `duration` defaults to the full source length (minus the trim start)."""
+    ff = ff or resolve_ffmpeg()
     src = Path(src)
     out_dir = Path(out_dir)
     out_dir.mkdir(parents=True, exist_ok=True)