diff --git a/av/pktque/buf.go b/av/pktque/buf.go
new file mode 100644
index 0000000..8be5f9a
--- /dev/null
+++ b/av/pktque/buf.go
@@ -0,0 +1,73 @@
+
+package pktque
+
+import (
+	"github.com/nareix/joy4/av"
+)
+
+type Buf struct {
+	Head, Tail BufPos
+	pkts []av.Packet
+	size, maxsize int
+}
+
+func NewBuf() *Buf {
+	return &Buf{
+		pkts: make([]av.Packet, 64),
+		maxsize: 1024*512,
+	}
+}
+
+func (self *Buf) SetMaxSize(size int) {
+	self.maxsize = size
+	self.shrink()
+}
+
+func (self *Buf) shrink() {
+	for self.size > self.maxsize && self.Head-self.Tail > 1 {
+		pkt := self.pkts[int(self.Head)&(len(self.pkts)-1)]
+		self.size -= len(pkt.Data)
+		self.Head++
+	}
+}
+
+func (self *Buf) grow() {
+	newpkts := make([]av.Packet, len(self.pkts)*2)
+	for i := self.Head; i.LT(self.Tail); i++ {
+		newpkts[int(i)&(len(newpkts)-1)] = self.pkts[int(i)&(len(self.pkts)-1)]
+	}
+	self.pkts = newpkts
+}
+
+func (self *Buf) Push(pkt av.Packet) {
+	if int(self.Tail-self.Head) == len(self.pkts) {
+		self.grow()
+	}
+	self.pkts[int(self.Tail)&(len(self.pkts)-1)] = pkt
+	self.Tail++
+	self.size += len(pkt.Data)
+	self.shrink()
+}
+
+func (self *Buf) Get(pos BufPos) av.Packet {
+	return self.pkts[int(pos)&(len(self.pkts)-1)]
+}
+
+func (self *Buf) IsValidPos(pos BufPos) bool {
+	return pos.GE(self.Head) && pos.LT(self.Tail)
+}
+
+type BufPos int
+
+func (self BufPos) LT(pos BufPos) bool {
+	return self - pos < 0
+}
+
+func (self BufPos) GE(pos BufPos) bool {
+	return self - pos >= 0
+}
+
+func (self BufPos) GT(pos BufPos) bool {
+	return self - pos > 0
+}
+
diff --git a/av/pubsub/queue.go b/av/pubsub/queue.go
index 2d312c4..473e823 100644
--- a/av/pubsub/queue.go
+++ b/av/pubsub/queue.go
@@ -4,6 +4,7 @@ package pubsub
 
 import (
 	"github.com/nareix/joy4/av"
+	"github.com/nareix/joy4/av/pktque"
 	"io"
 	"time"
 	"sync"
@@ -21,7 +22,7 @@ import (
 
 // One publisher and multiple subscribers thread-safe packet buffer queue.
 type Queue struct {
-	pkts []av.Packet
+	buf *pktque.Buf
 	head, tail int
 	lock *sync.RWMutex
 	cond *sync.Cond
@@ -33,6 +34,7 @@ type Queue struct {
 
 func NewQueue(streams []av.CodecData) *Queue {
 	q := &Queue{}
+	q.buf = pktque.NewBuf()
 	q.streams = streams
 	q.maxdur = time.Second*10
 	q.lock = &sync.RWMutex{}
@@ -46,32 +48,13 @@ func NewQueue(streams []av.CodecData) *Queue {
 	return q
 }
 
-// Set max buffered total packets duration.
-func (self *Queue) SetMaxDuration(dur time.Duration) {
+func (self *Queue) SetMaxSize(size int) {
 	self.lock.Lock()
-
-	self.maxdur = dur
-	for self.maxdur > 0 && len(self.pkts) >= 2 && self.pkts[len(self.pkts)-1].Time - self.pkts[0].Time > self.maxdur {
-		self.pkts = self.pkts[1:]
-		self.head++
-	}
-
+	self.buf.SetMaxSize(size)
 	self.lock.Unlock()
 	return
 }
 
-// Currently buffered packets total duration.
-func (self *Queue) Duration() (dur time.Duration) {
-	self.lock.RLock()
-
-	if len(self.pkts) >= 2 {
-		dur = self.pkts[len(self.pkts)-1].Time - self.pkts[0].Time
-	}
-
-	self.lock.RUnlock()
-	return
-}
-
 // After Close() called, all QueueCursor's ReadPacket will return io.EOF.
 func (self *Queue) Close() (err error) {
 	self.lock.Lock()
@@ -87,12 +70,7 @@ func (self *Queue) Close() (err error) {
 func (self *Queue) WritePacket(pkt av.Packet) (err error) {
 	self.lock.Lock()
 
-	if self.maxdur > 0 && len(self.pkts) >= 2 && self.pkts[len(self.pkts)-1].Time - self.pkts[0].Time > self.maxdur {
-		self.pkts = self.pkts[1:]
-		self.head++
-	}
-	self.pkts = append(self.pkts, pkt)
-	self.tail++
+	self.buf.Push(pkt)
 	self.cond.Broadcast()
 
 	self.lock.Unlock()
@@ -101,22 +79,22 @@ func (self *Queue) WritePacket(pkt av.Packet) (err error) {
 
 type QueueCursor struct {
 	que *Queue
-	pos int
-	init func(pkts []av.Packet, videoidx int) int
+	pos pktque.BufPos
+	gotpos bool
+	init func(buf *pktque.Buf, videoidx int) pktque.BufPos
 }
 
 func (self *Queue) newCursor() *QueueCursor {
 	return &QueueCursor{
 		que: self,
-		pos: -1,
 	}
 }
 
 // Create cursor position at latest packet.
 func (self *Queue) Latest() *QueueCursor {
 	cursor := self.newCursor()
-	cursor.init = func(pkts []av.Packet, videoidx int) int {
-		return len(pkts)
+	cursor.init = func(buf *pktque.Buf, videoidx int) pktque.BufPos {
+		return buf.Tail
 	}
 	return cursor
 }
@@ -124,8 +102,8 @@ func (self *Queue) Latest() *QueueCursor {
 // Create cursor position at oldest buffered packet.
 func (self *Queue) Oldest() *QueueCursor {
 	cursor := self.newCursor()
-	cursor.init = func(pkts []av.Packet, videoidx int) int {
-		return 0
+	cursor.init = func(buf *pktque.Buf, videoidx int) pktque.BufPos {
+		return buf.Head
 	}
 	return cursor
 }
@@ -133,14 +111,15 @@ func (self *Queue) Oldest() *QueueCursor {
 // Create cursor position at specific time in buffered packets.
 func (self *Queue) DelayedTime(dur time.Duration) *QueueCursor {
 	cursor := self.newCursor()
-	cursor.init = func(pkts []av.Packet, videoidx int) int {
-		i := len(self.pkts)-1
-		if i > 0 {
-			end := self.pkts[i]
-			for i--; i >= 0; i-- {
-				if end.Time - self.pkts[i].Time > dur {
+	cursor.init = func(buf *pktque.Buf, videoidx int) pktque.BufPos {
+		i := buf.Tail-1
+		if buf.IsValidPos(i) {
+			end := buf.Get(i)
+			for buf.IsValidPos(i) {
+				if end.Time - buf.Get(i).Time > dur {
 					break
 				}
+				i--
 			}
 		}
 		return i
@@ -151,12 +130,12 @@ func (self *Queue) DelayedTime(dur time.Duration) *QueueCursor {
 // Create cursor position at specific delayed GOP count in buffered packets.
 func (self *Queue) DelayedGopCount(n int) *QueueCursor {
 	cursor := self.newCursor()
-	cursor.init = func(pkts []av.Packet, videoidx int) int {
-		i := 0
+	cursor.init = func(buf *pktque.Buf, videoidx int) pktque.BufPos {
+		i := buf.Tail-1
 		if videoidx != -1 {
-			i = len(self.pkts)-1
-			for gop := 0; i >= 0 && gop < n; i-- {
-				if self.pkts[i].Idx == int8(self.videoidx) && self.pkts[i].IsKeyFrame {
+			for gop := 0; buf.IsValidPos(i) && gop < n; i-- {
+				pkt := buf.Get(i)
+				if pkt.Idx == int8(self.videoidx) && pkt.IsKeyFrame {
 					gop++
 				}
 			}
@@ -176,17 +155,19 @@ func (self *QueueCursor) Streams() (streams []av.CodecData, err error) {
 // ReadPacket will not consume packets in Queue, it's just a cursor.
 func (self *QueueCursor) ReadPacket() (pkt av.Packet, err error) {
 	self.que.cond.L.Lock()
-	if self.pos == -1 {
-		self.pos = self.init(self.que.pkts, self.que.videoidx)+self.que.head
+	buf := self.que.buf
+	if !self.gotpos {
+		self.pos = self.init(buf, self.que.videoidx)
+		self.gotpos = true
 	}
 	for {
-		if self.pos - self.que.head < 0 {
-			self.pos = self.que.head
-		} else if self.pos - self.que.tail > 0 {
-			self.pos = self.que.tail
+		if self.pos.LT(buf.Head) {
+			self.pos = buf.Head
+		} else if self.pos.GT(buf.Tail) {
+			self.pos = buf.Tail
 		}
-		if self.pos - self.que.head >= 0 && self.pos - self.que.tail < 0 {
-			pkt = self.que.pkts[self.pos - self.que.head]
+		if buf.IsValidPos(self.pos) {
+			pkt = buf.Get(self.pos)
 			self.pos++
 			break
 		}