Add warning about frame duration in autocue/ebur128 filter.

src/libs/autocue.liq

@@ -717,11 +717,31 @@ def autocue.internal.implementation(
 
       # Get very last frame for precise track duration
       frame = list.last(frames)
+      frame_duration =
+        float_of_string(
+          list.assoc(default="0.", "lavfi.liq.duration_time", frame)
+        )
+
+      frame_duration =
+        if
+          frame_duration != 100.
+        then
+          log.important(
+            label="autocue",
+            "Warning: reported frame duration should be 100ms. Either the FFmpeg \
+             ebur128 filter has changed its internals or the version/build of \
+             FFmpeg you are using is buggy. We recommend using a fairly recent \
+             distribution with FFmpeg version 7 or above. Backported packages \
+             can be tricky."
+          )
+          100.
+        else
+          frame_duration
+        end
+
       duration =
         float_of_string(list.assoc(default="0.", "lavfi.liq.pts_time", frame)) +
-          float_of_string(
-            list.assoc(default="0.", "lavfi.liq.duration_time", frame)
-          )
+          frame_duration
 
       # Finalize cue/cross/fade values now...
       if cue_out() == 0. then cue_out := duration end