diff --git a/av/format/flv/muxeravcaac.go b/av/format/flv/muxeravcaac.go
index 885ff9a..3d55377 100644
--- a/av/format/flv/muxeravcaac.go
+++ b/av/format/flv/muxeravcaac.go
@@ -132,16 +132,6 @@ func (muxer *MuxerAvcAac) muxVideoTag(frame *codec.Frame) error {
 	if frame.Payload[0]&0x1F == h264.NalSps {
 		if len(muxer.videoMeta.Sps) == 0 {
 			muxer.videoMeta.Sps = frame.Payload
-			var rawSps h264.RawSPS
-			err := rawSps.Decode(muxer.videoMeta.Sps)
-			if err != nil {
-				return err
-			}
-
-			muxer.videoMeta.Width = rawSps.Width()
-			muxer.videoMeta.Height = rawSps.Height()
-			muxer.videoMeta.FrameRate = rawSps.FrameRate()
-			muxer.dtsStep = 1000.0 / muxer.videoMeta.FrameRate
 		}
 		return muxer.muxSequenceHeaderTag()
 	}
@@ -277,11 +267,16 @@ func (muxer *MuxerAvcAac) muxSequenceHeaderTag() error {
 		return nil
 	}
 
-	if len(muxer.videoMeta.Sps) == 0 || len(muxer.videoMeta.Pps) == 0 {
+	if !h264.MetadataIsReady(&muxer.videoMeta) {
 		// not enough
 		return nil
 	}
 
+	if muxer.videoMeta.FixedFrameRate {
+		muxer.dtsStep = 1000.0 / muxer.videoMeta.FrameRate
+	} else { // TODO:
+		muxer.dtsStep = 1000.0 / 30
+	}
 	muxer.spsMuxed = true
 
 	record := NewAVCDecoderConfigurationRecord(muxer.videoMeta.Sps, muxer.videoMeta.Pps)
diff --git a/av/format/mpegts/muxeravcaac.go b/av/format/mpegts/muxeravcaac.go
index ac011b5..e06c860 100644
--- a/av/format/mpegts/muxeravcaac.go
+++ b/av/format/mpegts/muxeravcaac.go
@@ -32,6 +32,7 @@ type MuxerAvcAac struct {
 	recvQueue     *queue.SyncQueue
 	tsframeWriter FrameWriter
 	closed        bool
+	metaReady      bool
 	basePts       int64
 	nextDts       float64
 	dtsStep       float64
@@ -141,16 +142,7 @@ func (muxer *MuxerAvcAac) muxVideoTag(frame *codec.Frame) (err error) {
 		if len(muxer.videoMeta.Sps) == 0 {
 			muxer.videoMeta.Sps = frame.Payload
 		}
-		var rawSps h264.RawSPS
-		err = rawSps.Decode(muxer.videoMeta.Sps)
-		if err != nil {
-			return
-		}
-
-		muxer.videoMeta.Width = rawSps.Width()
-		muxer.videoMeta.Height = rawSps.Height()
-		muxer.videoMeta.FrameRate = rawSps.FrameRate()
-		muxer.dtsStep = 1000.0 / muxer.videoMeta.FrameRate
+		muxer.preparMetadata()
 		return
 	}
 
@@ -158,6 +150,7 @@ func (muxer *MuxerAvcAac) muxVideoTag(frame *codec.Frame) (err error) {
 		if len(muxer.videoMeta.Pps) == 0 {
 			muxer.videoMeta.Pps = frame.Payload
 		}
+		muxer.preparMetadata()
 		return
 	}
 
@@ -183,6 +176,24 @@ func (muxer *MuxerAvcAac) muxVideoTag(frame *codec.Frame) (err error) {
 	return muxer.tsframeWriter.WriteMpegtsFrame(tsframe)
 }
 
+func (muxer *MuxerAvcAac) preparMetadata() {
+	if muxer.metaReady {
+		return
+	}
+
+	if !h264.MetadataIsReady(&muxer.videoMeta) {
+		// not enough
+		return
+	}
+
+	if muxer.videoMeta.FixedFrameRate {
+		muxer.dtsStep = 1000.0 / muxer.videoMeta.FrameRate
+	} else { // TODO:
+		muxer.dtsStep = 1000.0 / 30
+	}
+	muxer.metaReady = true
+}
+
 func (muxer *MuxerAvcAac) muxAudioTag(frame *codec.Frame) error {
 	pts := frame.AbsTimestamp - muxer.basePts + ptsDelay
 	pts *= 90