Index: nicontroller.js
===================================================================
--- nicontroller.js	(リビジョン 38275)
+++ nicontroller.js	(作業コピー)
@@ -274,24 +274,38 @@
         return null;
     },
 
+    get _flvplayerInfo() {
+        var p = this._flvplayer();
+        if (p._NicoPlayerControllerInfo === undefined) {
+            p._NicoPlayerControllerInfo = {};
+        }
+        return p._NicoPlayerControllerInfo;
+    },
+
+    play: function(playStatus) {
+        var p = this._flvplayer();
+        p.ext_play(playStatus);
+        this._flvplayerInfo.playStatus = playStatus;
+    },
+
     togglePlay: function() {
         var p = this._flvplayer();
-        (p.ext_getStatus() !== this.constants.STATE_PLAYING)
-            ? p.ext_play(this.constants.PLAY)
-            : p.ext_play(this.constants.PAUSE);
+        if (p.ext_getStatus() === 'end') {
+            if (p.ext_getPlayheadTime() === p.ext_getTotalTime()) {
+                p.ext_setPlayheadTime(0);
+                this.play(this.constants.PLAY);
+                return;
+            }
+            this.play(! this._flvplayerInfo.playStatus);
+            return;
+        }
 
-        if(p.ext_getStatus() === 'end') {
-            let base = p.ext_getPlayheadTime();
-            let self = this;
-            setTimeout(function () {
-                if (base !== p.ext_getPlayheadTime()) {
-                    p.ext_play(self.constants.PAUSE);
-                } else {
-                    p.ext_setPlayheadTime(0);
-                    p.ext_play(self.constants.PLAY);
-                }
-            }, 100);
+        if (this._flvplayerInfo.playStatus === undefined && p.ext_getPlayheadTime() === 0) {
+            this.play(this.constants.PLAY);
+            return;
         }
+
+        this.play(p.ext_getStatus() !== this.constants.STATE_PLAYING ? this.constants.PLAY : this.constants.PAUSE);
     },
 
     toggleMute: function() {
@@ -369,6 +383,60 @@
 
     seekBy: function(delta) {
         if(delta) {
+            if (delta.match(/^(-?\d+)k$/)) {
+                delta = parseInt(RegExp.$1, this.constants.CARDINAL_NUMBER);
+                var p = this._flvplayer();
+                var position = p.ext_getPlayheadTime();
+                if (delta < 0) {
+                    if (position == 0) {
+                        return;
+                    }
+                    var prePosition = position;
+                    function waitProc(cond, proc, interval) {
+                        function func() {
+                            if (cond()) {
+                                proc();
+                            }
+                            else {
+                                setTimeout(func, interval);
+                            }
+                        }
+                        func();
+                    }
+                    function seekAndWait(proc) {
+                        waitProc(function() { return p.ext_getStatus() !== 'seeking'; }, proc, 0);
+                    }
+                    function seekWhile(cond, onNext, onFinish) {
+                        function func(pos) {
+                            var nextPos = onNext(pos);
+                            if (nextPos < 0) {
+                                nextPos = 0;
+                            }
+                            p.ext_setPlayheadTime(nextPos);
+                            function proc() {
+                                var tmpPosition = p.ext_getPlayheadTime();
+                                if (cond(tmpPosition)) {
+                                    func(tmpPosition);
+                                }
+                                else {
+                                    onFinish(tmpPosition);
+                                }
+                            }
+                            seekAndWait(proc);
+                        }
+                        func();
+                    }
+                    function onFinish(finishPos) {
+                        //seekWhile(function(pos) { return pos < prePosition; }, function(pos) { return (position = (pos ? pos : finishPos)) + 1; }, function() { p.ext_setPlayheadTime(position); });
+                    }
+                    seekWhile(function(pos) { return pos >= prePosition; }, function() { return position -= 5; }, onFinish);
+                }
+                else {
+                    position += 1;
+                    p.ext_setPlayheadTime(position);
+                }
+                return;
+            }
             if(isNaN(delta)) throw new Error('assign signed number : seekBy()');
         }
         else delta = this.constants.SEEKBY_DEFAULT;
@@ -377,6 +445,12 @@
         var position = p.ext_getPlayheadTime();
         position += parseInt(delta, this.constants.CARDINAL_NUMBER);
 
+        if (position < 0) {
+            position = 0;
+        }
+        else if (position > p.ext_getTotalTime()) {
+            position = p.ext_getTotalTime();
+        }
         p.ext_setPlayheadTime(position);
     },