diff --git a/dali/operators/reader/loader/video/frames_decoder.cc b/dali/operators/reader/loader/video/frames_decoder.cc
index cc510fbaed..f989d9a2dc 100644
--- a/dali/operators/reader/loader/video/frames_decoder.cc
+++ b/dali/operators/reader/loader/video/frames_decoder.cc
@@ -396,6 +396,7 @@ void FramesDecoder::BuildIndex() {
           }
         }
       } else {
+        // for other formats it is enough to check (packet->flags & AV_PKT_FLAG_KEY)
         entry.is_keyframe = true;
       }
     } else {