diff --git a/scenes/thumbnails.py b/scenes/thumbnails.py
index 1d70123..0cb5f06 100644
--- a/scenes/thumbnails.py
+++ b/scenes/thumbnails.py
@@ -17,7 +17,10 @@ logger = logging.getLogger(__name__)
 THUMB_INTERVAL_SECONDS = 1.0
 THUMB_MAX_HEIGHT = 360
 THUMB_JPEG_QUALITY = 9
-CLIP_SELECT_CHUNK_SIZE = 30
+# ffmpeg's select filter decodes the whole clip on every pass, so each chunk is
+# a full re-decode. Keep it one pass (one decode) for all but absurdly long clips
+# — a single select expression with thousands of terms is cheap to evaluate.
+CLIP_SELECT_CHUNK_SIZE = 4096
 
 
 def _otio_frames(rational_time):