diff --git a/trunk/src/app/srs_app_source.cpp b/trunk/src/app/srs_app_source.cpp
index 9654f0e38..3cba64bbf 100644
--- a/trunk/src/app/srs_app_source.cpp
+++ b/trunk/src/app/srs_app_source.cpp
@@ -246,6 +246,8 @@ void SrsMessageQueue::shrink()
     
     // no iframe, for audio, clear the queue.
     // it is ok to clear for audio, for the shrink tell us the queue is full.
+    // for video, we clear util the I-Frame, for the decoding must start from I-frame,
+    // for audio, it's ok to clear any data, also we can clear the whole queue.
     // @see: https://github.com/winlinvip/simple-rtmp-server/issues/134
     if (iframe_index < 0) {
         clear();