diff --git a/README b/README
index ab1937d..a53a913 100644
--- a/README
+++ b/README
@@ -4,8 +4,19 @@ You can find free video streaming multicast ip addresses with Oh! Multicast
 Video Scanner.
 
 omvs scans all multicast ip addresses the user specifies and if omvs finds
-something, omvs tries to decode it with gstreamer and save it as png file in
-the output directory. Root privilege is required to run omvs.
+something, omvs tries to decode it with gstreamer and saves it as png file in
+the output directory. There are many cases omvs finds something but png file is
+not stored. Such as, the video is scrambled(encrypted, not free), multicasting
+data doesn't contain video(audio only, data only), gstreamer doesn't recognize
+it(unknown codec), etc. If you increase the number of jobs with "-j" command
+line option, you can scan faster. However, You need take caution, because it
+can cause network congestion.
+
+As omvs uses libpcap to capture raw packet, root privilege is required to run
+omvs.
+
+Run "./configure ; make" to build omvs. Run "./omvs" with scanning multicast ip
+addresses.
 
 e.g.)
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