default not to preview the stream for publisher.

@@ -47,7 +47,7 @@
             <input type="text" id="txt_url" class="input-xxlarge" value=""></input>
             <button class="btn btn-primary" id="btn_publish">发布视频</button>
             <label class="checkbox">
-                <input type="checkbox" id="cb_preview" checked>预览
+                <input type="checkbox" id="cb_preview">预览
             </label>
         </div>
     </div>