diff --git a/netStream.go b/netStream.go
index 28526b0..c53388f 100644
--- a/netStream.go
+++ b/netStream.go
@@ -152,18 +152,18 @@ func processRtmp(conn net.Conn) {
 						err = nc.SendMessage(SEND_PLAY_RESPONSE_MESSAGE, newPlayResponseMessageData(nc.streamID, NetStream_Play_Reset, Level_Status))
 						err = nc.SendMessage(SEND_PLAY_RESPONSE_MESSAGE, newPlayResponseMessageData(nc.streamID, NetStream_Play_Start, Level_Status))
 						vt, at := subscriber.WaitVideoTrack(), subscriber.WaitAudioTrack()
-						var lastTimeStamp uint32
-						var getDeltaTime func(uint32) uint32
-						getDeltaTime = func(ts uint32) (t uint32) {
-							lastTimeStamp = ts
+						if vt != nil {
+							var lastTimeStamp uint32
+							var getDeltaTime func(uint32) uint32
 							getDeltaTime = func(ts uint32) (t uint32) {
-								t = ts - lastTimeStamp
 								lastTimeStamp = ts
+								getDeltaTime = func(ts uint32) (t uint32) {
+									t = ts - lastTimeStamp
+									lastTimeStamp = ts
+									return
+								}
 								return
 							}
-							return
-						}
-						if vt != nil {
 							err = nc.SendMessage(SEND_FULL_VDIEO_MESSAGE, &AVPack{Payload: vt.ExtraData.Payload})
 							subscriber.OnVideo = func(pack engine.VideoPack) {
 								err = nc.SendMessage(SEND_FULL_VDIEO_MESSAGE, &AVPack{Timestamp: 0, Payload: pack.Payload})
@@ -173,6 +173,17 @@ func processRtmp(conn net.Conn) {
 							}
 						}
 						if at != nil {
+							var lastTimeStamp uint32
+							var getDeltaTime func(uint32) uint32
+							getDeltaTime = func(ts uint32) (t uint32) {
+								lastTimeStamp = ts
+								getDeltaTime = func(ts uint32) (t uint32) {
+									t = ts - lastTimeStamp
+									lastTimeStamp = ts
+									return
+								}
+								return
+							}
 							subscriber.OnAudio = func(pack engine.AudioPack) {
 								if at.CodecID == 10 {
 									err = nc.SendMessage(SEND_FULL_AUDIO_MESSAGE, &AVPack{Payload: at.ExtraData})