diff --git a/include/media/IAudioFlinger.h b/include/media/IAudioFlinger.h
index 2bae08e..8239b0e 100644
--- a/include/media/IAudioFlinger.h
+++ b/include/media/IAudioFlinger.h
@@ -45,8 +45,9 @@
 
     // or-able bits shared by createTrack and openRecord, but not all combinations make sense
     enum {
-        TRACK_DEFAULT = 0,
-        TRACK_TIMED   = 1,
+        TRACK_DEFAULT = 0,  // client requests a default AudioTrack
+        TRACK_TIMED   = 1,  // client requests a TimedAudioTrack
+        TRACK_FAST    = 2,  // client requests a fast AudioTrack
     };
     typedef uint32_t track_flags_t;