Extract frames at full resolution before transcoding clip for browser

Previously frames were extracted after the 720p transcode, resulting in 1280x720
images even when the source was 4K. Now frames are extracted from the original
clip first, then the clip is transcoded to 720p for web playback.

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

app/watcher.py

@@ -109,13 +109,19 @@ def _frame_score(frame: np.ndarray, plates: list) -> float:
 
 
 def _process_clip(event_id: str, event_dir: str, clip_path: str, camera_name: str = None):
-    """Process an existing clip: transcode, extract frames, LPR, store in DB."""
+    """Process an existing clip: extract frames at full res, transcode for browser, LPR, store in DB."""
     if camera_name is None:
         camera_name = CAMERA_NAME
 
     frames_pattern = os.path.join(event_dir, "frame_%04d.jpg")
 
-    # Transcode to H.264 baseline for browser compatibility
+    # Extract frames at full original resolution BEFORE any transcode
+    subprocess.run([
+        "ffmpeg", "-y", "-i", clip_path,
+        "-vf", f"fps={CAPTURE_FPS}", "-q:v", "2", frames_pattern,
+    ], capture_output=True, timeout=60)
+
+    # Transcode to H.264 baseline 720p for browser (after frame extraction)
     web_clip = os.path.join(event_dir, "clip_web.mp4")
     subprocess.run([
         "ffmpeg", "-y", "-i", clip_path,
@@ -131,12 +137,6 @@ def _process_clip(event_id: str, event_dir: str, clip_path: str, camera_name: st
     else:
         log.warning("Transcode failed, keeping raw clip")
 
-    # Extract frames
-    subprocess.run([
-        "ffmpeg", "-y", "-i", clip_path,
-        "-vf", f"fps={CAPTURE_FPS}", "-q:v", "2", frames_pattern,
-    ], capture_output=True, timeout=60)
-
     frame_files = sorted(glob.glob(os.path.join(event_dir, "frame_*.jpg")))
     log.info(f"Extracted {len(frame_files)} frames")