diff --git a/format/rtspv2/demuxer.go b/format/rtspv2/demuxer.go
index e59c453..05ea449 100644
--- a/format/rtspv2/demuxer.go
+++ b/format/rtspv2/demuxer.go
@@ -343,12 +343,10 @@ func (client *RTSPClient) appendPlaybackVideoPacket(retmap []*av.Packet, nal []b
 					prePkt[i].RealTimestamp = client.preKeyRealVideoTs * 1000
 					client.iterateDruation = 0
 				}
-				client.iterateDruation += prePkt[i].Duration
 			} else {
 				prePkt[i].RealTimestamp = client.preKeyRealVideoTs*1000 + client.iterateDruation.Milliseconds()
-				client.iterateDruation += prePkt[i].Duration
 			}
-
+			client.iterateDruation += prePkt[i].Duration
 			client.preRealVideoMs = prePkt[i].RealTimestamp
 			// fmt.Println("playback duration",
 			// 	prePkt[i].IsKeyFrame,