diff --git a/av/pktque/filters.go b/av/pktque/filters.go
new file mode 100644
index 0000000..40a33b5
--- /dev/null
+++ b/av/pktque/filters.go
@@ -0,0 +1,167 @@
+
+package pktque
+
+import (
+	"time"
+	"github.com/nareix/joy4/av"
+)
+
+type Filter interface {
+	ModifyPacket(pkt *av.Packet, streams []av.CodecData, videoidx int, audioidx int) (drop bool, err error)
+}
+
+type Filters []Filter
+
+func (self Filters) ModifyPacket(pkt *av.Packet, streams []av.CodecData, videoidx int, audioidx int) (drop bool, err error) {
+	for _, filter := range self {
+		if drop, err = filter.ModifyPacket(pkt, streams, videoidx, audioidx); err != nil {
+			return
+		}
+		if drop {
+			return
+		}
+	}
+	return
+}
+
+type FilterDemuxer struct {
+	av.Demuxer
+	Filter Filter
+	streams []av.CodecData
+	videoidx int
+	audioidx int
+}
+
+func (self FilterDemuxer) ReadPacket() (pkt av.Packet, err error) {
+	if self.streams == nil {
+		if self.streams, err = self.Demuxer.Streams(); err != nil {
+			return
+		}
+		for i, stream := range self.streams {
+			if stream.Type().IsVideo() {
+				self.videoidx = i
+			} else if stream.Type().IsAudio() {
+				self.audioidx = i
+			}
+		}
+	}
+
+	for {
+		if pkt, err = self.Demuxer.ReadPacket(); err != nil {
+			return
+		}
+		var drop bool
+		if drop, err = self.Filter.ModifyPacket(&pkt, self.streams, self.videoidx, self.audioidx); err != nil {
+			return
+		}
+		if !drop {
+			break
+		}
+	}
+
+	return
+}
+
+type WaitKeyFrame struct {
+	ok bool
+}
+
+func (self *WaitKeyFrame) ModifyPacket(pkt *av.Packet, streams []av.CodecData, videoidx int, audioidx int) (drop bool, err error) {
+	if !self.ok && pkt.Idx == int8(videoidx) && pkt.IsKeyFrame {
+		self.ok = true
+	}
+	drop = !self.ok
+	return
+}
+
+type TimeStartFromZero struct {
+	timebase time.Duration
+}
+
+func (self *TimeStartFromZero) ModifyPacket(pkt *av.Packet, streams []av.CodecData, videoidx int, audioidx int) (drop bool, err error) {
+	if self.timebase == 0 {
+		self.timebase = pkt.Time
+	}
+	pkt.Time -= self.timebase
+	return
+}
+
+type AVSync struct {
+	MaxTimeDiff time.Duration
+	time []time.Duration
+	timebase time.Duration
+}
+
+func (self *AVSync) ModifyPacket(pkt *av.Packet, streams []av.CodecData, videoidx int, audioidx int) (drop bool, err error) {
+	if self.time == nil {
+		self.time = make([]time.Duration, len(streams))
+		if self.MaxTimeDiff == 0 {
+			self.MaxTimeDiff = time.Millisecond*500
+		}
+	}
+
+	start, end, correctable, correcttime := self.check(int(pkt.Idx))
+	time := pkt.Time - self.timebase
+	if time >= start && time < end {
+		pkt.Time = time
+		self.time[pkt.Idx] = time
+	} else {
+		if correctable {
+			self.timebase = pkt.Time - correcttime
+			pkt.Time = correcttime
+			self.time[pkt.Idx] = correcttime
+		} else {
+			drop = true
+		}
+	}
+
+	return
+}
+
+func (self *AVSync) check(i int) (start time.Duration, end time.Duration, correctable bool, correcttime time.Duration) {
+	minidx := -1
+	maxidx := -1
+	for j := range self.time {
+		if minidx == -1 || self.time[j] < self.time[minidx] {
+			minidx = j
+		}
+		if maxidx == -1 || self.time[j] > self.time[maxidx] {
+			maxidx = j
+		}
+	}
+	allthesame := self.time[minidx] == self.time[maxidx]
+
+	if i == minidx {
+		if allthesame {
+			correctable = true
+		} else {
+			correctable = false
+		}
+	} else {
+		correctable = true
+	}
+
+	start = self.time[minidx]
+	end = start + self.MaxTimeDiff
+	correcttime = start + time.Millisecond*40
+	return
+}
+
+type Walltime struct {
+	firsttime time.Time
+}
+
+func (self *Walltime) ModifyPacket(pkt *av.Packet, streams []av.CodecData, videoidx int, audioidx int) (drop bool, err error) {
+	if pkt.Idx == 0 {
+		if self.firsttime.IsZero() {
+			self.firsttime = time.Now()
+		}
+		pkttime := self.firsttime.Add(pkt.Time)
+		delta := pkttime.Sub(time.Now())
+		if delta > 0 {
+			time.Sleep(delta)
+		}
+	}
+	return
+}
+