diff --git a/box.go b/box.go
index 8fd1288..beac0fd 100644
--- a/box.go
+++ b/box.go
@@ -12,62 +12,62 @@ const LengthUnlimited = math.MaxUint32
 
 type ICustomFieldObject interface {
 	// GetFieldSize returns size of dynamic field
-	GetFieldSize(name string, bss *BoxStructureStatus) uint
+	GetFieldSize(name string, bss BoxStructureStatus) uint
 
 	// GetFieldLength returns length of dynamic field
-	GetFieldLength(name string, bss *BoxStructureStatus) uint
+	GetFieldLength(name string, bss BoxStructureStatus) uint
 
 	// IsOptFieldEnabled check whether if the optional field is enabled
-	IsOptFieldEnabled(name string, bss *BoxStructureStatus) bool
+	IsOptFieldEnabled(name string, bss BoxStructureStatus) bool
 
 	// StringifyField returns field value as string
-	StringifyField(name string, indent string, depth int, bss *BoxStructureStatus) (string, bool)
+	StringifyField(name string, indent string, depth int, bss BoxStructureStatus) (string, bool)
 
-	IsPString(name string, bytes []byte, remainingSize uint64, bss *BoxStructureStatus) bool
+	IsPString(name string, bytes []byte, remainingSize uint64, bss BoxStructureStatus) bool
 
-	BeforeUnmarshal(r io.ReadSeeker, size uint64, bss *BoxStructureStatus) (n uint64, override bool, err error)
+	BeforeUnmarshal(r io.ReadSeeker, size uint64, bss BoxStructureStatus) (n uint64, override bool, err error)
 
-	OnReadField(name string, r bitio.ReadSeeker, leftBits uint64, bss *BoxStructureStatus) (rbits uint64, override bool, err error)
+	OnReadField(name string, r bitio.ReadSeeker, leftBits uint64, bss BoxStructureStatus) (rbits uint64, override bool, err error)
 
-	OnWriteField(name string, w bitio.Writer, bss *BoxStructureStatus) (wbits uint64, override bool, err error)
+	OnWriteField(name string, w bitio.Writer, bss BoxStructureStatus) (wbits uint64, override bool, err error)
 }
 
 type BaseCustomFieldObject struct {
 }
 
 // GetFieldSize returns size of dynamic field
-func (box *BaseCustomFieldObject) GetFieldSize(string, *BoxStructureStatus) uint {
+func (box *BaseCustomFieldObject) GetFieldSize(string, BoxStructureStatus) uint {
 	panic(errors.New("GetFieldSize not implemented"))
 }
 
 // GetFieldLength returns length of dynamic field
-func (box *BaseCustomFieldObject) GetFieldLength(string, *BoxStructureStatus) uint {
+func (box *BaseCustomFieldObject) GetFieldLength(string, BoxStructureStatus) uint {
 	panic(errors.New("GetFieldLength not implemented"))
 }
 
 // IsOptFieldEnabled check whether if the optional field is enabled
-func (box *BaseCustomFieldObject) IsOptFieldEnabled(string, *BoxStructureStatus) bool {
+func (box *BaseCustomFieldObject) IsOptFieldEnabled(string, BoxStructureStatus) bool {
 	return false
 }
 
 // StringifyField returns field value as string
-func (box *BaseCustomFieldObject) StringifyField(string, string, int, *BoxStructureStatus) (string, bool) {
+func (box *BaseCustomFieldObject) StringifyField(string, string, int, BoxStructureStatus) (string, bool) {
 	return "", false
 }
 
-func (*BaseCustomFieldObject) IsPString(name string, bytes []byte, remainingSize uint64, bss *BoxStructureStatus) bool {
+func (*BaseCustomFieldObject) IsPString(name string, bytes []byte, remainingSize uint64, bss BoxStructureStatus) bool {
 	return true
 }
 
-func (*BaseCustomFieldObject) BeforeUnmarshal(io.ReadSeeker, uint64, *BoxStructureStatus) (uint64, bool, error) {
+func (*BaseCustomFieldObject) BeforeUnmarshal(io.ReadSeeker, uint64, BoxStructureStatus) (uint64, bool, error) {
 	return 0, false, nil
 }
 
-func (*BaseCustomFieldObject) OnReadField(string, bitio.ReadSeeker, uint64, *BoxStructureStatus) (uint64, bool, error) {
+func (*BaseCustomFieldObject) OnReadField(string, bitio.ReadSeeker, uint64, BoxStructureStatus) (uint64, bool, error) {
 	return 0, false, nil
 }
 
-func (*BaseCustomFieldObject) OnWriteField(string, bitio.Writer, *BoxStructureStatus) (uint64, bool, error) {
+func (*BaseCustomFieldObject) OnWriteField(string, bitio.Writer, BoxStructureStatus) (uint64, bool, error) {
 	return 0, false, nil
 }
 
diff --git a/box_types.go b/box_types.go
index 2df2262..e4d8d9e 100644
--- a/box_types.go
+++ b/box_types.go
@@ -31,7 +31,7 @@ func (*Co64) GetType() BoxType {
 }
 
 // GetFieldLength returns length of dynamic field
-func (co64 *Co64) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (co64 *Co64) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "ChunkOffset":
 		return uint(co64.EntryCount)
@@ -59,7 +59,7 @@ type Colr struct {
 	Unknown                 []byte  `mp4:"size=8,opt=dynamic"`
 }
 
-func (colr *Colr) IsOptFieldEnabled(name string, bss *BoxStructureStatus) bool {
+func (colr *Colr) IsOptFieldEnabled(name string, bss BoxStructureStatus) bool {
 	switch colr.ColourType {
 	case [4]byte{'n', 'c', 'l', 'x'}:
 		switch name {
@@ -111,7 +111,7 @@ func (*Ctts) GetType() BoxType {
 }
 
 // GetFieldLength returns length of dynamic field
-func (ctts *Ctts) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (ctts *Ctts) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		return uint(ctts.EntryCount)
@@ -231,7 +231,7 @@ func (*Elst) GetType() BoxType {
 }
 
 // GetFieldSize returns size of dynamic field
-func (elst *Elst) GetFieldSize(name string, bss *BoxStructureStatus) uint {
+func (elst *Elst) GetFieldSize(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		switch elst.GetVersion() {
@@ -253,7 +253,7 @@ func (elst *Elst) GetFieldSize(name string, bss *BoxStructureStatus) uint {
 }
 
 // GetFieldLength returns length of dynamic field
-func (elst *Elst) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (elst *Elst) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		return uint(elst.EntryCount)
@@ -282,7 +282,7 @@ type Emsg struct {
 	MessageData           []byte `mp4:"size=8,string"`
 }
 
-func (emsg *Emsg) OnReadField(name string, r bitio.ReadSeeker, leftBits uint64, bss *BoxStructureStatus) (rbits uint64, override bool, err error) {
+func (emsg *Emsg) OnReadField(name string, r bitio.ReadSeeker, leftBits uint64, bss BoxStructureStatus) (rbits uint64, override bool, err error) {
 	if emsg.GetVersion() == 0 {
 		return
 	}
@@ -306,7 +306,7 @@ func (emsg *Emsg) OnReadField(name string, r bitio.ReadSeeker, leftBits uint64,
 	}
 }
 
-func (emsg *Emsg) OnWriteField(name string, w bitio.Writer, bss *BoxStructureStatus) (wbits uint64, override bool, err error) {
+func (emsg *Emsg) OnWriteField(name string, w bitio.Writer, bss BoxStructureStatus) (wbits uint64, override bool, err error) {
 	if emsg.GetVersion() == 0 {
 		return
 	}
@@ -371,7 +371,7 @@ type Descriptor struct {
 }
 
 // GetFieldLength returns length of dynamic field
-func (ds *Descriptor) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (ds *Descriptor) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Data":
 		return uint(ds.Size)
@@ -379,7 +379,7 @@ func (ds *Descriptor) GetFieldLength(name string, bss *BoxStructureStatus) uint
 	panic(fmt.Errorf("invalid name of dynamic-length field: boxType=esds fieldName=%s", name))
 }
 
-func (ds *Descriptor) IsOptFieldEnabled(name string, bss *BoxStructureStatus) bool {
+func (ds *Descriptor) IsOptFieldEnabled(name string, bss BoxStructureStatus) bool {
 	switch ds.Tag {
 	case ESDescrTag:
 		return name == "ESDescriptor"
@@ -391,7 +391,7 @@ func (ds *Descriptor) IsOptFieldEnabled(name string, bss *BoxStructureStatus) bo
 }
 
 // StringifyField returns field value as string
-func (ds *Descriptor) StringifyField(name string, indent string, depth int, bss *BoxStructureStatus) (string, bool) {
+func (ds *Descriptor) StringifyField(name string, indent string, depth int, bss BoxStructureStatus) (string, bool) {
 	switch name {
 	case "Tag":
 		switch ds.Tag {
@@ -424,7 +424,7 @@ type ESDescriptor struct {
 	OCRESID              uint16 `mp4:"size=16,opt=dynamic"`
 }
 
-func (esds *ESDescriptor) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (esds *ESDescriptor) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "URLString":
 		return uint(esds.URLLength)
@@ -432,7 +432,7 @@ func (esds *ESDescriptor) GetFieldLength(name string, bss *BoxStructureStatus) u
 	panic(fmt.Errorf("invalid name of dynamic-length field: boxType=ESDescriptor fieldName=%s", name))
 }
 
-func (esds *ESDescriptor) IsOptFieldEnabled(name string, bss *BoxStructureStatus) bool {
+func (esds *ESDescriptor) IsOptFieldEnabled(name string, bss BoxStructureStatus) bool {
 	switch name {
 	case "DependsOnESID":
 		return esds.StreamDependenceFlag
@@ -536,7 +536,7 @@ func (*Hdlr) GetType() BoxType {
 	return BoxTypeHdlr()
 }
 
-func (hdlr *Hdlr) IsPString(name string, bytes []byte, remainingSize uint64, bss *BoxStructureStatus) bool {
+func (hdlr *Hdlr) IsPString(name string, bytes []byte, remainingSize uint64, bss BoxStructureStatus) bool {
 	switch name {
 	case "Name":
 		return remainingSize == 0 && hdlr.PreDefined != 0
@@ -666,7 +666,7 @@ func (*Meta) GetType() BoxType {
 	return BoxTypeMeta()
 }
 
-func (meta *Meta) BeforeUnmarshal(r io.ReadSeeker, size uint64, bss *BoxStructureStatus) (n uint64, override bool, err error) {
+func (meta *Meta) BeforeUnmarshal(r io.ReadSeeker, size uint64, bss BoxStructureStatus) (n uint64, override bool, err error) {
 	// for Apple Quick Time
 	buf := make([]byte, 4)
 	if _, err := io.ReadFull(r, buf); err != nil {
@@ -844,7 +844,7 @@ func (*Mvhd) GetType() BoxType {
 }
 
 // StringifyField returns field value as string
-func (mvhd *Mvhd) StringifyField(name string, indent string, depth int, bss *BoxStructureStatus) (string, bool) {
+func (mvhd *Mvhd) StringifyField(name string, indent string, depth int, bss BoxStructureStatus) (string, bool) {
 	switch name {
 	case "Rate":
 		return strconv.FormatFloat(mvhd.GetRate(), 'f', -1, 32), true
@@ -886,7 +886,7 @@ type PsshKID struct {
 }
 
 // GetFieldLength returns length of dynamic field
-func (pssh *Pssh) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (pssh *Pssh) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "KIDs":
 		return uint(pssh.KIDCount)
@@ -897,7 +897,7 @@ func (pssh *Pssh) GetFieldLength(name string, bss *BoxStructureStatus) uint {
 }
 
 // StringifyField returns field value as string
-func (pssh *Pssh) StringifyField(name string, indent string, depth int, bss *BoxStructureStatus) (string, bool) {
+func (pssh *Pssh) StringifyField(name string, indent string, depth int, bss BoxStructureStatus) (string, bool) {
 	switch name {
 	case "SystemID":
 		buf := bytes.NewBuffer(nil)
@@ -969,7 +969,7 @@ type VisualSampleEntry struct {
 }
 
 // StringifyField returns field value as string
-func (vse *VisualSampleEntry) StringifyField(name string, indent string, depth int, bss *BoxStructureStatus) (string, bool) {
+func (vse *VisualSampleEntry) StringifyField(name string, indent string, depth int, bss BoxStructureStatus) (string, bool) {
 	switch name {
 	case "Compressorname":
 		if vse.Compressorname[0] <= 31 {
@@ -993,18 +993,18 @@ type AudioSampleEntry struct {
 	QuickTimeData []byte    `mp4:"size=8,opt=dynamic,len=dynamic"`
 }
 
-func (ase *AudioSampleEntry) IsOptFieldEnabled(name string, bss *BoxStructureStatus) bool {
+func (ase *AudioSampleEntry) IsOptFieldEnabled(name string, bss BoxStructureStatus) bool {
 	if name == "QuickTimeData" {
-		return bss != nil && bss.IsQuickTimeCompatible && (bss.UnderWave || ase.EntryVersion == 1 || ase.EntryVersion == 2)
+		return bss.IsQuickTimeCompatible && (bss.UnderWave || ase.EntryVersion == 1 || ase.EntryVersion == 2)
 	}
-	if bss != nil && bss.IsQuickTimeCompatible && bss.UnderWave {
+	if bss.IsQuickTimeCompatible && bss.UnderWave {
 		return false
 	}
 	return true
 }
 
-func (ase *AudioSampleEntry) GetFieldLength(name string, bss *BoxStructureStatus) uint {
-	if name == "QuickTimeData" && bss != nil && bss.IsQuickTimeCompatible {
+func (ase *AudioSampleEntry) GetFieldLength(name string, bss BoxStructureStatus) uint {
+	if name == "QuickTimeData" && bss.IsQuickTimeCompatible {
 		if bss.UnderWave {
 			return LengthUnlimited
 		} else if ase.EntryVersion == 1 {
@@ -1049,7 +1049,7 @@ type AVCDecoderConfiguration struct {
 	SequenceParameterSetsExt     []AVCParameterSet `mp4:"len=dynamic,opt=dynamic"`
 }
 
-func (avcc *AVCDecoderConfiguration) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (avcc *AVCDecoderConfiguration) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "SequenceParameterSets":
 		return uint(avcc.NumOfSequenceParameterSets)
@@ -1061,7 +1061,7 @@ func (avcc *AVCDecoderConfiguration) GetFieldLength(name string, bss *BoxStructu
 	return 0
 }
 
-func (avcc *AVCDecoderConfiguration) IsOptFieldEnabled(name string, bss *BoxStructureStatus) bool {
+func (avcc *AVCDecoderConfiguration) IsOptFieldEnabled(name string, bss BoxStructureStatus) bool {
 	switch name {
 	case "Reserved3",
 		"ChromaFormat",
@@ -1076,7 +1076,7 @@ func (avcc *AVCDecoderConfiguration) IsOptFieldEnabled(name string, bss *BoxStru
 	return false
 }
 
-func (avcc *AVCDecoderConfiguration) OnReadField(name string, r bitio.ReadSeeker, leftBits uint64, bss *BoxStructureStatus) (rbits uint64, override bool, err error) {
+func (avcc *AVCDecoderConfiguration) OnReadField(name string, r bitio.ReadSeeker, leftBits uint64, bss BoxStructureStatus) (rbits uint64, override bool, err error) {
 	if name == "HighProfileFieldsEnabled" {
 		avcc.HighProfileFieldsEnabled = leftBits >= 32 &&
 			(avcc.Profile == AVCHighProfile ||
@@ -1088,7 +1088,7 @@ func (avcc *AVCDecoderConfiguration) OnReadField(name string, r bitio.ReadSeeker
 	return 0, false, nil
 }
 
-func (avcc *AVCDecoderConfiguration) OnWriteField(name string, w bitio.Writer, bss *BoxStructureStatus) (wbits uint64, override bool, err error) {
+func (avcc *AVCDecoderConfiguration) OnWriteField(name string, w bitio.Writer, bss BoxStructureStatus) (wbits uint64, override bool, err error) {
 	if name == "HighProfileFieldsEnabled" {
 		if avcc.HighProfileFieldsEnabled &&
 			avcc.Profile != AVCHighProfile &&
@@ -1108,7 +1108,7 @@ type AVCParameterSet struct {
 	NALUnit []byte `mp4:"size=8,len=dynamic"`
 }
 
-func (s *AVCParameterSet) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (s *AVCParameterSet) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "NALUnit":
 		return uint(s.Length)
@@ -1143,7 +1143,7 @@ type SbgpEntry struct {
 	GroupDescriptionIndex uint32 `mp4:"size=32"`
 }
 
-func (sbgp *Sbgp) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (sbgp *Sbgp) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		return uint(sbgp.EntryCount)
@@ -1239,7 +1239,7 @@ type TemporalLevelEntryL struct {
 	TemporalLevelEntry `mp4:"extend"`
 }
 
-func (sgpd *Sgpd) GetFieldSize(name string, bss *BoxStructureStatus) uint {
+func (sgpd *Sgpd) GetFieldSize(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "AlternativeStartupEntries":
 		return uint(sgpd.DefaultLength * 8)
@@ -1247,7 +1247,7 @@ func (sgpd *Sgpd) GetFieldSize(name string, bss *BoxStructureStatus) uint {
 	return 0
 }
 
-func (sgpd *Sgpd) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (sgpd *Sgpd) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "RollDistances", "RollDistancesL",
 		"AlternativeStartupEntries", "AlternativeStartupEntriesL",
@@ -1258,7 +1258,7 @@ func (sgpd *Sgpd) GetFieldLength(name string, bss *BoxStructureStatus) uint {
 	return 0
 }
 
-func (sgpd *Sgpd) IsOptFieldEnabled(name string, bss *BoxStructureStatus) bool {
+func (sgpd *Sgpd) IsOptFieldEnabled(name string, bss BoxStructureStatus) bool {
 	noDefaultLength := sgpd.Version == 1 && sgpd.DefaultLength == 0
 	rollDistances := sgpd.GroupingType == [4]byte{'r', 'o', 'l', 'l'} ||
 		sgpd.GroupingType == [4]byte{'p', 'r', 'o', 'l'}
@@ -1296,7 +1296,7 @@ func (*Sgpd) GetType() BoxType {
 	return BoxTypeSgpd()
 }
 
-func (entry *AlternativeStartupEntry) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (entry *AlternativeStartupEntry) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "SampleOffset":
 		return uint(entry.RollCount)
@@ -1304,7 +1304,7 @@ func (entry *AlternativeStartupEntry) GetFieldLength(name string, bss *BoxStruct
 	return 0
 }
 
-func (entry *AlternativeStartupEntryL) GetFieldSize(name string, bss *BoxStructureStatus) uint {
+func (entry *AlternativeStartupEntryL) GetFieldSize(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "AlternativeStartupEntry":
 		return uint(entry.DescriptionLength * 8)
@@ -1346,7 +1346,7 @@ func (*Sidx) GetType() BoxType {
 	return BoxTypeSidx()
 }
 
-func (sidx *Sidx) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (sidx *Sidx) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "References":
 		return uint(sidx.ReferenceCount)
@@ -1389,7 +1389,7 @@ func (*Smhd) GetType() BoxType {
 }
 
 // StringifyField returns field value as string
-func (smhd *Smhd) StringifyField(name string, indent string, depth int, bss *BoxStructureStatus) (string, bool) {
+func (smhd *Smhd) StringifyField(name string, indent string, depth int, bss BoxStructureStatus) (string, bool) {
 	switch name {
 	case "Balance":
 		return strconv.FormatFloat(float64(smhd.GetBalance()), 'f', -1, 32), true
@@ -1447,7 +1447,7 @@ func (*Stco) GetType() BoxType {
 }
 
 // GetFieldLength returns length of dynamic field
-func (stco *Stco) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (stco *Stco) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "ChunkOffset":
 		return uint(stco.EntryCount)
@@ -1482,7 +1482,7 @@ func (*Stsc) GetType() BoxType {
 }
 
 // GetFieldLength returns length of dynamic field
-func (stsc *Stsc) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (stsc *Stsc) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		return uint(stsc.EntryCount)
@@ -1529,7 +1529,7 @@ func (*Stss) GetType() BoxType {
 }
 
 // GetFieldLength returns length of dynamic field
-func (stss *Stss) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (stss *Stss) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "SampleNumber":
 		return uint(stss.EntryCount)
@@ -1559,7 +1559,7 @@ func (*Stsz) GetType() BoxType {
 }
 
 // GetFieldLength returns length of dynamic field
-func (stsz *Stsz) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (stsz *Stsz) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "EntrySize":
 		if stsz.SampleSize == 0 {
@@ -1597,7 +1597,7 @@ func (*Stts) GetType() BoxType {
 }
 
 // GetFieldLength returns length of dynamic field
-func (stts *Stts) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (stts *Stts) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		return uint(stts.EntryCount)
@@ -1716,7 +1716,7 @@ func (*Tfra) GetType() BoxType {
 }
 
 // GetFieldSize returns size of dynamic field
-func (tfra *Tfra) GetFieldSize(name string, bss *BoxStructureStatus) uint {
+func (tfra *Tfra) GetFieldSize(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "TrafNumber":
 		return (uint(tfra.LengthSizeOfTrafNum) + 1) * 8
@@ -1746,7 +1746,7 @@ func (tfra *Tfra) GetFieldSize(name string, bss *BoxStructureStatus) uint {
 }
 
 // GetFieldLength returns length of dynamic field
-func (tfra *Tfra) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (tfra *Tfra) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		return uint(tfra.NumberOfEntry)
@@ -1794,7 +1794,7 @@ func (*Tkhd) GetType() BoxType {
 }
 
 // StringifyField returns field value as string
-func (tkhd *Tkhd) StringifyField(name string, indent string, depth int, bss *BoxStructureStatus) (string, bool) {
+func (tkhd *Tkhd) StringifyField(name string, indent string, depth int, bss BoxStructureStatus) (string, bool) {
 	switch name {
 	case "Width":
 		return strconv.FormatFloat(tkhd.GetWidth(), 'f', -1, 32), true
@@ -1917,7 +1917,7 @@ func (*Trun) GetType() BoxType {
 }
 
 // GetFieldSize returns size of dynamic field
-func (trun *Trun) GetFieldSize(name string, bss *BoxStructureStatus) uint {
+func (trun *Trun) GetFieldSize(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		var size uint
@@ -1940,7 +1940,7 @@ func (trun *Trun) GetFieldSize(name string, bss *BoxStructureStatus) uint {
 }
 
 // GetFieldLength returns length of dynamic field
-func (trun *Trun) GetFieldLength(name string, bss *BoxStructureStatus) uint {
+func (trun *Trun) GetFieldLength(name string, bss BoxStructureStatus) uint {
 	switch name {
 	case "Entries":
 		return uint(trun.SampleCount)
diff --git a/box_types_test.go b/box_types_test.go
index db36e62..0836e2e 100644
--- a/box_types_test.go
+++ b/box_types_test.go
@@ -2437,14 +2437,14 @@ func TestBoxTypes(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			// Marshal
 			buf := bytes.NewBuffer(nil)
-			n, err := Marshal(buf, tc.src, &tc.bss)
+			n, err := Marshal(buf, tc.src, tc.bss)
 			require.NoError(t, err)
 			assert.Equal(t, uint64(len(tc.bin)), n)
 			assert.Equal(t, tc.bin, buf.Bytes())
 
 			// Unmarshal
 			r := bytes.NewReader(tc.bin)
-			n, err = Unmarshal(r, uint64(len(tc.bin)), tc.dst, &tc.bss)
+			n, err = Unmarshal(r, uint64(len(tc.bin)), tc.dst, tc.bss)
 			require.NoError(t, err)
 			assert.Equal(t, uint64(buf.Len()), n)
 			assert.Equal(t, tc.src, tc.dst)
@@ -2453,7 +2453,7 @@ func TestBoxTypes(t *testing.T) {
 			assert.Equal(t, int64(buf.Len()), s)
 
 			// UnmarshalAny
-			dst, n, err := UnmarshalAny(bytes.NewReader(tc.bin), tc.src.GetType(), uint64(len(tc.bin)), &tc.bss)
+			dst, n, err := UnmarshalAny(bytes.NewReader(tc.bin), tc.src.GetType(), uint64(len(tc.bin)), tc.bss)
 			require.NoError(t, err)
 			assert.Equal(t, uint64(buf.Len()), n)
 			assert.Equal(t, tc.src, dst)
@@ -2462,7 +2462,7 @@ func TestBoxTypes(t *testing.T) {
 			assert.Equal(t, int64(buf.Len()), s)
 
 			// Stringify
-			str, err := Stringify(tc.src, &tc.bss)
+			str, err := Stringify(tc.src, tc.bss)
 			require.NoError(t, err)
 			assert.Equal(t, tc.str, str)
 		})
@@ -2534,7 +2534,7 @@ func TestHdlrUnmarshalHandlerName(t *testing.T) {
 			// unmarshal
 			dst := Hdlr{}
 			r := bytes.NewReader(bin)
-			n, err := Unmarshal(r, uint64(len(bin)), &dst, nil)
+			n, err := Unmarshal(r, uint64(len(bin)), &dst, BoxStructureStatus{})
 			assert.NoError(t, err)
 			assert.Equal(t, uint64(len(bin)), n)
 			assert.Equal(t, [4]byte{'v', 'i', 'd', 'e'}, dst.HandlerType)
@@ -2555,7 +2555,7 @@ func TestMetaMarshalAppleQuickTime(t *testing.T) {
 	// unmarshal
 	dst := Meta{}
 	r := bytes.NewReader(bin)
-	n, err := Unmarshal(r, uint64(len(bin)), &dst, nil)
+	n, err := Unmarshal(r, uint64(len(bin)), &dst, BoxStructureStatus{})
 	assert.NoError(t, err)
 	assert.Equal(t, uint64(0), n)
 	s, _ := r.Seek(0, io.SeekCurrent)
@@ -2598,7 +2598,7 @@ func TestAvcCInconsistentError(t *testing.T) {
 		},
 	}
 	buf := bytes.NewBuffer(nil)
-	_, err := Marshal(buf, avcc, nil)
+	_, err := Marshal(buf, avcc, BoxStructureStatus{})
 	require.Error(t, err)
 	assert.Equal(t, "each values of Profile and HighProfileFieldsEnabled are inconsistent", err.Error())
 }
diff --git a/extract.go b/extract.go
index 5dcadc6..5e3001b 100644
--- a/extract.go
+++ b/extract.go
@@ -26,9 +26,9 @@ func ExtractBoxesWithPayload(r io.ReadSeeker, parent *BoxInfo, paths []BoxPath)
 			return nil, err
 		}
 
-		var bss *BoxStructureStatus
+		var bss BoxStructureStatus
 		if parent != nil {
-			bss = &parent.BoxStructureStatus
+			bss = parent.BoxStructureStatus
 		}
 		box, _, err := UnmarshalAny(r, bi.Type, bi.Size-bi.HeaderSize, bss)
 		if err != nil {
diff --git a/marshaller.go b/marshaller.go
index ed3551e..1045bd6 100644
--- a/marshaller.go
+++ b/marshaller.go
@@ -23,10 +23,10 @@ type marshaller struct {
 	writer bitio.Writer
 	wbits  uint64
 	src    IImmutableBox
-	bss    *BoxStructureStatus
+	bss    BoxStructureStatus
 }
 
-func Marshal(w io.Writer, src IImmutableBox, bss *BoxStructureStatus) (n uint64, err error) {
+func Marshal(w io.Writer, src IImmutableBox, bss BoxStructureStatus) (n uint64, err error) {
 	t := reflect.TypeOf(src).Elem()
 	v := reflect.ValueOf(src).Elem()
 
@@ -259,10 +259,10 @@ type unmarshaller struct {
 	dst    IBox
 	size   uint64
 	rbits  uint64
-	bss    *BoxStructureStatus
+	bss    BoxStructureStatus
 }
 
-func UnmarshalAny(r io.ReadSeeker, boxType BoxType, payloadSize uint64, bss *BoxStructureStatus) (box IBox, n uint64, err error) {
+func UnmarshalAny(r io.ReadSeeker, boxType BoxType, payloadSize uint64, bss BoxStructureStatus) (box IBox, n uint64, err error) {
 	if dst, err := boxType.New(); err != nil {
 		return nil, 0, err
 	} else {
@@ -271,7 +271,7 @@ func UnmarshalAny(r io.ReadSeeker, boxType BoxType, payloadSize uint64, bss *Box
 	}
 }
 
-func Unmarshal(r io.ReadSeeker, payloadSize uint64, dst IBox, bss *BoxStructureStatus) (n uint64, err error) {
+func Unmarshal(r io.ReadSeeker, payloadSize uint64, dst IBox, bss BoxStructureStatus) (n uint64, err error) {
 	t := reflect.TypeOf(dst).Elem()
 	v := reflect.ValueOf(dst).Elem()
 
@@ -687,7 +687,7 @@ type fieldConfig struct {
 	hidden     bool
 }
 
-func readFieldConfig(box IImmutableBox, parent reflect.Value, fieldName string, tag fieldTag, bss *BoxStructureStatus) (config fieldConfig, err error) {
+func readFieldConfig(box IImmutableBox, parent reflect.Value, fieldName string, tag fieldTag, bss BoxStructureStatus) (config fieldConfig, err error) {
 	config.name = fieldName
 	cfo, ok := parent.Addr().Interface().(ICustomFieldObject)
 	if ok {
@@ -825,7 +825,7 @@ func parseFieldTag(str string) fieldTag {
 	return tag
 }
 
-func isTargetField(box IImmutableBox, config fieldConfig, bss *BoxStructureStatus) bool {
+func isTargetField(box IImmutableBox, config fieldConfig, bss BoxStructureStatus) bool {
 	if box.GetVersion() != anyVersion {
 		if config.version != anyVersion && box.GetVersion() != config.version {
 			return false
diff --git a/marshaller_test.go b/marshaller_test.go
index dda266d..7d04bee 100644
--- a/marshaller_test.go
+++ b/marshaller_test.go
@@ -21,7 +21,7 @@ func (m *mockBox) GetType() BoxType {
 	return m.Type
 }
 
-func (m *mockBox) GetFieldSize(n string, bss *BoxStructureStatus) uint {
+func (m *mockBox) GetFieldSize(n string, bss BoxStructureStatus) uint {
 	if s, ok := m.DynSizeMap[n]; !ok {
 		panic(fmt.Errorf("invalid name of dynamic-size field: %s", n))
 	} else {
@@ -29,7 +29,7 @@ func (m *mockBox) GetFieldSize(n string, bss *BoxStructureStatus) uint {
 	}
 }
 
-func (m *mockBox) GetFieldLength(n string, bss *BoxStructureStatus) uint {
+func (m *mockBox) GetFieldLength(n string, bss BoxStructureStatus) uint {
 	if l, ok := m.DynLenMap[n]; !ok {
 		panic(fmt.Errorf("invalid name of dynamic-length field: %s", n))
 	} else {
@@ -180,14 +180,14 @@ func TestMarshal(t *testing.T) {
 
 	// marshal
 	buf := &bytes.Buffer{}
-	n, err := Marshal(buf, &src, nil)
+	n, err := Marshal(buf, &src, BoxStructureStatus{})
 	require.NoError(t, err)
 	assert.Equal(t, uint64(len(bin)), n)
 	assert.Equal(t, bin, buf.Bytes())
 
 	// unmarshal
 	dst := testBox{mockBox: mb}
-	n, err = Unmarshal(bytes.NewReader(bin), uint64(len(bin)+8), &dst, nil)
+	n, err = Unmarshal(bytes.NewReader(bin), uint64(len(bin)+8), &dst, BoxStructureStatus{})
 	assert.NoError(t, err)
 	assert.Equal(t, uint64(len(bin)), n)
 	assert.Equal(t, src, dst)
@@ -229,7 +229,7 @@ func TestUnsupportedBoxVersionErr(t *testing.T) {
 		}
 
 		dst := testBox{mockBox: mb}
-		n, err := Unmarshal(bytes.NewReader(bin), uint64(len(bin)+8), &dst, nil)
+		n, err := Unmarshal(bytes.NewReader(bin), uint64(len(bin)+8), &dst, BoxStructureStatus{})
 
 		if e.enabled {
 			assert.NoError(t, err, "version=%d", e.version)
@@ -631,7 +631,7 @@ func TestReadFieldConfig(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			v := reflect.ValueOf(tc.box).Elem()
-			config, err := readFieldConfig(tc.box, v, tc.fieldName, tc.fieldTag, nil)
+			config, err := readFieldConfig(tc.box, v, tc.fieldName, tc.fieldTag, BoxStructureStatus{})
 			if tc.err {
 				assert.Error(t, err)
 				return
diff --git a/probe.go b/probe.go
index d639838..51cf297 100644
--- a/probe.go
+++ b/probe.go
@@ -106,7 +106,7 @@ func probeTkhd(r io.ReadSeeker, bi *BoxInfo, info *TrackInfo) error {
 	}
 
 	tkhd := Tkhd{}
-	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tkhd, &bi.BoxStructureStatus)
+	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tkhd, bi.BoxStructureStatus)
 	if err != nil {
 		return err
 	}
@@ -126,7 +126,7 @@ func probeMdhd(r io.ReadSeeker, bi *BoxInfo, info *TrackInfo) error {
 	}
 
 	mdhd := Mdhd{}
-	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &mdhd, &bi.BoxStructureStatus)
+	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &mdhd, bi.BoxStructureStatus)
 	if err != nil {
 		return err
 	}
@@ -183,7 +183,7 @@ func probeTfhd(r io.ReadSeeker, bi *BoxInfo, segment *SegmentInfo) error {
 	}
 
 	tfhd := Tfhd{}
-	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tfhd, &bi.BoxStructureStatus)
+	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tfhd, bi.BoxStructureStatus)
 	if err != nil {
 		return err
 	}
@@ -200,7 +200,7 @@ func probeTfdt(r io.ReadSeeker, bi *BoxInfo, segment *SegmentInfo) error {
 	}
 
 	tfdt := Tfdt{}
-	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tfdt, &bi.BoxStructureStatus)
+	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tfdt, bi.BoxStructureStatus)
 	if err != nil {
 		return err
 	}
@@ -220,7 +220,7 @@ func probeTrun(r io.ReadSeeker, bi *BoxInfo, segment *SegmentInfo) error {
 	}
 
 	trun := Trun{}
-	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &trun, &bi.BoxStructureStatus)
+	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &trun, bi.BoxStructureStatus)
 	if err != nil {
 		return err
 	}
@@ -263,7 +263,7 @@ func probeTfra(r io.ReadSeeker, bi *BoxInfo, info *FraProbeInfo) error {
 	}
 
 	tfra := Tfra{}
-	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tfra, &bi.BoxStructureStatus)
+	_, err := Unmarshal(r, bi.Size-bi.HeaderSize, &tfra, bi.BoxStructureStatus)
 	if err != nil {
 		return err
 	}
diff --git a/read.go b/read.go
index 15e582b..0065691 100644
--- a/read.go
+++ b/read.go
@@ -54,7 +54,7 @@ func readBoxStructureFromInternal(r io.ReadSeeker, bi *BoxInfo, path BoxPath, ha
 	// check comatible-brands
 	if len(path) == 0 && bi.Type == BoxTypeFtyp() {
 		var ftyp Ftyp
-		if _, err := Unmarshal(r, bi.Size-bi.HeaderSize, &ftyp, &bi.BoxStructureStatus); err != nil {
+		if _, err := Unmarshal(r, bi.Size-bi.HeaderSize, &ftyp, bi.BoxStructureStatus); err != nil {
 			return nil, err
 		}
 		for _, cb := range ftyp.CompatibleBrands {
@@ -88,7 +88,7 @@ func readBoxStructureFromInternal(r io.ReadSeeker, bi *BoxInfo, path BoxPath, ha
 			return nil, 0, err
 		}
 
-		if box, n, err := UnmarshalAny(r, bi.Type, bi.Size-bi.HeaderSize, &bi.BoxStructureStatus); err != nil {
+		if box, n, err := UnmarshalAny(r, bi.Type, bi.Size-bi.HeaderSize, bi.BoxStructureStatus); err != nil {
 			return nil, 0, err
 		} else {
 			childrenOffset = bi.Offset + bi.HeaderSize + n
@@ -114,7 +114,7 @@ func readBoxStructureFromInternal(r io.ReadSeeker, bi *BoxInfo, path BoxPath, ha
 				return nil, err
 			}
 
-			if _, n, err := UnmarshalAny(r, bi.Type, bi.Size-bi.HeaderSize, &bi.BoxStructureStatus); err != nil {
+			if _, n, err := UnmarshalAny(r, bi.Type, bi.Size-bi.HeaderSize, bi.BoxStructureStatus); err != nil {
 				return nil, err
 			} else {
 				childrenOffset = bi.Offset + bi.HeaderSize + n
diff --git a/string.go b/string.go
index 69f89e1..0370ce0 100644
--- a/string.go
+++ b/string.go
@@ -12,14 +12,14 @@ type stringfier struct {
 	buf    *bytes.Buffer
 	src    IImmutableBox
 	indent string
-	bss    *BoxStructureStatus
+	bss    BoxStructureStatus
 }
 
-func Stringify(src IImmutableBox, bss *BoxStructureStatus) (string, error) {
+func Stringify(src IImmutableBox, bss BoxStructureStatus) (string, error) {
 	return StringifyWithIndent(src, "", bss)
 }
 
-func StringifyWithIndent(src IImmutableBox, indent string, bss *BoxStructureStatus) (string, error) {
+func StringifyWithIndent(src IImmutableBox, indent string, bss BoxStructureStatus) (string, error) {
 	t := reflect.TypeOf(src).Elem()
 	v := reflect.ValueOf(src).Elem()
 
diff --git a/string_test.go b/string_test.go
index 0e86da2..01ee5eb 100644
--- a/string_test.go
+++ b/string_test.go
@@ -54,7 +54,7 @@ func TestEmsgStringify(t *testing.T) {
 		Bool:  true,
 	}
 
-	str, err := StringifyWithIndent(&box, " ", nil)
+	str, err := StringifyWithIndent(&box, " ", BoxStructureStatus{})
 	require.NoError(t, err)
 	assert.Equal(t, ` Version=0`+"\n"+
 		` Flags=0x000000`+"\n"+
@@ -74,7 +74,7 @@ func TestEmsgStringify(t *testing.T) {
 		` Array="hoge"`+"\n"+
 		` Bool=true`+"\n", str)
 
-	str, err = Stringify(&box, nil)
+	str, err = Stringify(&box, BoxStructureStatus{})
 	require.NoError(t, err)
 	assert.Equal(t, `Version=0 Flags=0x000000 String="abema.tv" Int32=-1234567890 Int32Hex=0x12345678 Uint32=1234567890 Bytes="abema" Ptr={Uint64=0x1234567890} Uint64=0x1234567890 Struct={Uint64=0x1234567890} Uint64=0x1234567890 Array="hoge" Bool=true`, str)
 }