for #367, design the config for exec.

@@ -919,6 +919,26 @@ vhost same.vhost.forward.srs.com {
     forward         127.0.0.1:1936 127.0.0.1:1937;
 }
 
+# the vhost for exec, fork process when publish stream.
+vhost exec.srs.com {
+    # the exec used to fork process when got some event.
+    exec {
+        # whether enable the exec.
+        # default: off.
+        enabled     off;
+        # when publish stream, exec the process with variables:
+        #       [vhost] the input stream vhost.
+        #       [port] the intput stream port.
+        #       [app] the input stream app.
+        #       [stream] the input stream name.
+        #       [engine] the tanscode engine name.
+        # other variables for exec only:
+        #       [url] the rtmp url which trigger the publish.
+        # @remark empty to ignore this exec.
+        publish     ./objs/ffmpeg/bin/ffmpeg -f flv -i [url] -vcodec copy -acodec copy -f flv ./[stream].flv;
+    }
+}
+
 # the main comments for transcode
 vhost example.transcode.srs.com {
     # the streaming transcode configs.