fix: normalize video fps to 24000/1001 with ffprobe check

extract.py

@@ -37,12 +37,75 @@ OUT_DIR    = os.path.join(os.path.dirname(os.path.abspath(__file__)), "extracted
 #   inter-frame only, and FFV1/PCM/ProRes/DNxHR have no GPU implementation.
 #   GPU only makes sense for preview proxies, not for measurement. CPU encode
 #   of 90 s clips is fast enough and bit-exact.
-VIDEO_CODEC = ["-c:v", "ffv1", "-level", "3", "-pix_fmt", "yuv444p"]
+VIDEO_CODEC_BASE = ["-c:v", "ffv1", "-level", "3", "-pix_fmt", "yuv444p"]
 AUDIO_CODEC = ["-c:a", "pcm_f32le", "-ar", "48000", "-ac", "1"]
+TARGET_FPS = "24000/1001"            # Blu-ray film = 23.976023... (shown as 23.98)
+TARGET_FPS_FLOAT = 24000 / 1001
+FPS_EPS = 0.02                        # tolerance for float comparison
+
+def _parse_rate(s: str) -> float | None:
+    s = s.strip()
+    if not s or s in ("0/0", "0"):
+        return None
+    if "/" in s:
+        try:
+            n, d = s.split("/")
+            return float(n) / float(d) if float(d) != 0 else None
+        except ValueError:
+            return None
+    try:
+        return float(s)
+    except ValueError:
+        return None
+
+def probe_fps(path: str) -> float | None:
+    """Return probed video fps via ffprobe, or None if probe fails."""
+    if shutil.which("ffprobe") is None:
+        return None
+    # avg_frame_rate is usually canonical; fall back to r_frame_rate
+    for entry in ("avg_frame_rate", "r_frame_rate"):
+        try:
+            r = subprocess.run(
+                ["ffprobe", "-v", "error", "-select_streams", "v:0",
+                 "-show_entries", f"stream={entry}", "-of", "default=nw=1:nk=1", path],
+                capture_output=True, text=True, timeout=10
+            )
+            for line in r.stdout.strip().splitlines():
+                fps = _parse_rate(line)
+                if fps and fps > 0 and fps < 1000:
+                    return fps
+        except Exception:
+            continue
+    return None
+
+def fps_matches(a: float | None, b: float, eps: float = FPS_EPS) -> bool:
+    return a is not None and abs(a - b) < eps
+
 # ─── Check ffmpeg ───
 if shutil.which(f"ffmpeg") is None:
     sys.exit(f"ERROR: 'ffmpeg' not found on PATH. Install it and try again.")
 
+# ─── Pre-probe all inputs to decide fps handling ───
+probed = {}
+for p in INPUT_FILES:
+    fps = probe_fps(p) if os.path.exists(p) else None
+    probed[p] = fps
+    tag = f"{fps:.3f}" if fps else "unknown (ffprobe missing or file not found)"
+    print(f"[probe] {os.path.basename(p)}: {tag} fps" + (f" {'≈ target ' + TARGET_FPS if fps_matches(fps, TARGET_FPS_FLOAT) else '≠ target ' + TARGET_FPS}" if fps else ""))
+
+# sanity check: both mismatch target and differ from each other → warn (neither is canonical)
+valid_fps = [v for v in probed.values() if v is not None]
+if len(valid_fps) >= 2:
+    all_match = all(fps_matches(v, TARGET_FPS_FLOAT) for v in valid_fps)
+    any_mismatch = any(not fps_matches(v, TARGET_FPS_FLOAT) for v in valid_fps)
+    if any_mismatch:
+        distinct = len({round(v, 2) for v in valid_fps}) > 1
+        if not all_match and distinct:
+            print(f"WARNING: inputs have different non-target fps {valid_fps} — both will be normalized to {TARGET_FPS} ({TARGET_FPS_FLOAT:.6f} fps). "
+                  f"If this is PAL speedup (25) vs NTSC film (24000/1001), consider also compensating audio tempo.")
+        elif not all_match:
+            print(f"NOTE: inputs share fps {valid_fps[0]:.3f} but differ from target {TARGET_FPS} — both will be normalized to {TARGET_FPS}.")
+
 # ─── Prepare output folder ───
 os.makedirs(OUT_DIR, exist_ok=True)
 
@@ -59,13 +122,25 @@ for INPUT_FILE in INPUT_FILES:
     print(f"-" * 50)
 
     # ─── Extract video-only (first 90s, no audio, CPU FFV1 re-encode) ───
+    # Only apply fps filter if probed fps differs from target (avoid needless re-timing)
+    fps = probed.get(INPUT_FILE)
+    needs_fps = not fps_matches(fps, TARGET_FPS_FLOAT)
+    video_codec = VIDEO_CODEC_BASE + (["-vf", f"fps={TARGET_FPS}:round=near", "-vsync", "cfr"] if needs_fps else [])
+    if fps is not None:
+        print(f"[fps] {stem}: probed {fps:.3f} → {'convert to ' + TARGET_FPS if needs_fps else 'already ' + TARGET_FPS + ', keeping native timing'}")
+    else:
+        print(f"[fps] {stem}: unknown fps → forcing {TARGET_FPS} (safe fallback)")
+        # ensure fallback forces target if we couldn't probe
+        if not needs_fps:
+            video_codec = VIDEO_CODEC_BASE + ["-vf", f"fps={TARGET_FPS}:round=near", "-vsync", "cfr"]
+
     cmd_video = [
         "ffmpeg",
         "-y",               # overwrite output
         "-i", INPUT_FILE,
         "-t", str(DURATION),
         "-an",              # no audio
-        *VIDEO_CODEC,       # ffv1 lossless intra-only, CPU (no GPU equiv.)
+        *video_codec,       # ffv1 lossless intra-only, CPU (no GPU equiv.)
         video_out
     ]
     print(f"[video: {stem}] running ffmpeg…")