Index: app.c
===================================================================
--- app.c	(revision 18783)
+++ app.c	(working copy)
@@ -555,6 +555,7 @@
 	int gotsilence = 0;		/* did we timeout for silence? */
 	int rfmt=0;
 	struct ast_silence_generator *silgen = NULL;
+	int no_audio = 0;
 
 	if (silencethreshold < 0)
 		silencethreshold = global_silence_threshold;
@@ -645,6 +646,7 @@
 				if (!res) {
 					ast_log(LOG_WARNING, "No audio available on %s??\n", chan->name);
 					res = -1;
+					no_audio = 1;
 				}
 			}
 
@@ -736,6 +738,8 @@
 		ast_channel_stop_silence_generator(chan, silgen);
 
 	*duration = end - start;
+	if (no_audio && *duration >= 4)
+		*duration -= 4;
 
 	for (x=0;x<fmtcnt;x++) {
 		if (!others[x])