refine the ui buffer effect

@@ -266,6 +266,8 @@ function __srs_on_player_timer(id, time, buffer_length) {
     buffer_length = Math.max(0, buffer_length);
     buffer_length = Math.min(player.buffer_time, buffer_length);
     
+    time = Math.max(0, time);
+    
     // user may override the on_player_timer, 
     // so set the data before invoke it.
     player.time = time;

@@ -94,6 +94,7 @@
                 srs_player = new SrsPlayer("player_id", url, 
                     srs_get_player_width(), srs_get_player_height());
                 srs_player.on_player_ready = function() {
+                    select_buffer_time("#btn_bt_0_8", 0.8);
                     srs_player.play();
                 }
                 srs_player.on_player_metadata = function(metadata) {
@@ -105,11 +106,6 @@
                     var buffer = buffer_length / srs_player.buffer_time * 100;
                     $("#pb_buffer").width(Number(buffer).toFixed(1) + "%");
                     
-                    // @remark, hack the default buffer time.
-                    if (!__active_bt && time > 3) {
-                        select_buffer_time("#btn_bt_2", 2);
-                    }
-                    
                     $("#pb_buffer_bg").attr("title", 
                         "缓冲区长度:" + Number(buffer_length).toFixed(1) + "秒(" 
                         + Number(buffer).toFixed(1) + "%)");