update readme

@@ -43,6 +43,8 @@ step 6: play live stream auto transcoded<br/>
 <pre>
 rtmp url: rtmp://127.0.0.1:1935/live/livestream_fast
 m3u8 url: http://127.0.0.1:80/live/livestream_fast.m3u8
+rtmp url: rtmp://127.0.0.1:1935/live/livestream_sd
+m3u8 url: http://127.0.0.1:80/live/livestream_sd.m3u8
 </pre>
 
 ### System Requirements

@@ -20,14 +20,14 @@ vhost __defaultVhost__ {
         enabled     on;
         ffmpeg      ./objs/ffmpeg/bin/ffmpeg;
         #ffmpeg      ./research/ffempty/ffempty;
-        engine fd{
+        engine fast{
             enabled         on;
             vcodec          libx264;
             vbitrate        300;
             vfps            20;
             vwidth          480;
             vheight         320;
-            vthreads        2;
+            vthreads        1;
             vprofile        baseline;
             vpreset         superfast;
             vparams {
@@ -40,6 +40,26 @@ vhost __defaultVhost__ {
             }
             output          rtmp://[vhost]:[port]/[app]/[stream]_fast;
         }
+        engine sd{
+            enabled         on;
+            vcodec          libx264;
+            vbitrate        500;
+            vfps            20;
+            vwidth          720;
+            vheight         480;
+            vthreads        1;
+            vprofile        main;
+            vpreset         fast;
+            vparams {
+            }
+            acodec          libaacplus;
+            abitrate        40;
+            asample_rate    44100;
+            achannels       2;
+            aparams {
+            }
+            output          rtmp://[vhost]:[port]/[app]/[stream]_sd;
+        }
     }
 }
 # transcode all app and stream of vhost