diff --git a/scripts/avsync.py b/scripts/avsync.py
index 32189da..d453194 100644
--- a/scripts/avsync.py
+++ b/scripts/avsync.py
@@ -219,8 +219,11 @@ def main() -> int:
     print(f"video   {video:8.3f} s")
     print(f"audio   {audio:8.3f} s")
     print(f"delta   {diff:+8.3f} s  ({pct:+.2f}% of the video length)")
-    verdict = "lengths match" if abs(diff) < 0.05 else "LENGTH MISMATCH — a clock problem"
-    print(f"        {verdict}")
+    if abs(diff) < 0.05:
+        print("        lengths match")
+    else:
+        print("        LENGTH MISMATCH — a clock problem, UNLESS a negative lip-sync offset is set:")
+        print(f"        trimming the stream head by N ms makes the audio track N ms shorter by design")
     for start, wlag, wcorr in windows:
         mark = "*" if wcorr >= 0.35 else " "
         print(f"        {start:5.1f}s {wlag:+7.0f} ms  corr {wcorr:.2f} {mark}")