diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 3e10496bee..d1d47631c0 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -621,7 +621,7 @@ typedef struct AVStream {
     /**
      * Format-specific stream ID.
      * decoding: set by libavformat
-     * encoding: set by the user
+     * encoding: set by the user, replaced by libavformat if left unset
      */
     int id;
     /**