diff --git a/pkg/formats/fmp4/boxes.go b/pkg/formats/fmp4/boxes.go
deleted file mode 100644
index 2efa686..0000000
--- a/pkg/formats/fmp4/boxes.go
+++ /dev/null
@@ -1,35 +0,0 @@
-//nolint:gochecknoinits,revive,gocritic
-package fmp4
-
-import (
-	gomp4 "github.com/abema/go-mp4"
-)
-
-func BoxTypeMp4v() gomp4.BoxType { return gomp4.StrToBoxType("mp4v") }
-
-func init() {
-	gomp4.AddAnyTypeBoxDef(&gomp4.VisualSampleEntry{}, BoxTypeMp4v())
-}
-
-func BoxTypeAC3() gomp4.BoxType { return gomp4.StrToBoxType("ac-3") }
-func BoxTypeDA3() gomp4.BoxType { return gomp4.StrToBoxType("dac3") }
-
-type Dac3 struct {
-	gomp4.Box
-	Fscod       uint8 `mp4:"0,size=2"`
-	Bsid        uint8 `mp4:"1,size=5"`
-	Bsmod       uint8 `mp4:"2,size=3"`
-	Acmod       uint8 `mp4:"3,size=3"`
-	LfeOn       uint8 `mp4:"4,size=1"`
-	BitRateCode uint8 `mp4:"5,size=5"`
-	Reserved    uint8 `mp4:"6,size=5,const=0"`
-}
-
-func (Dac3) GetType() gomp4.BoxType {
-	return BoxTypeDA3()
-}
-
-func init() {
-	gomp4.AddAnyTypeBoxDef(&gomp4.AudioSampleEntry{}, BoxTypeAC3())
-	gomp4.AddBoxDef(&Dac3{})
-}
diff --git a/pkg/formats/fmp4/init.go b/pkg/formats/fmp4/init.go
index 2f71f3b..0c96c5c 100644
--- a/pkg/formats/fmp4/init.go
+++ b/pkg/formats/fmp4/init.go
@@ -478,7 +478,7 @@ func (i *Init) Unmarshal(byts []byte) error {
 			if err != nil {
 				return nil, err
 			}
-			dac3 := box.(*Dac3)
+			dac3 := box.(*mp4.Dac3)
 
 			curTrack.Codec = &CodecAC3{
 				SampleRate:   sampleRate,
diff --git a/pkg/formats/fmp4/init_track.go b/pkg/formats/fmp4/init_track.go
index f68c6b0..7ae7521 100644
--- a/pkg/formats/fmp4/init_track.go
+++ b/pkg/formats/fmp4/init_track.go
@@ -482,7 +482,7 @@ func (track *InitTrack) marshal(w *mp4Writer) error {
 		_, err = w.writeBoxStart(&mp4.VisualSampleEntry{ // <mp4v>
 			SampleEntry: mp4.SampleEntry{
 				AnyTypeBox: mp4.AnyTypeBox{
-					Type: BoxTypeMp4v(),
+					Type: mp4.BoxTypeMp4v(),
 				},
 				DataReferenceIndex: 1,
 			},
@@ -538,7 +538,7 @@ func (track *InitTrack) marshal(w *mp4Writer) error {
 		_, err = w.writeBoxStart(&mp4.VisualSampleEntry{ // <mp4v>
 			SampleEntry: mp4.SampleEntry{
 				AnyTypeBox: mp4.AnyTypeBox{
-					Type: BoxTypeMp4v(),
+					Type: mp4.BoxTypeMp4v(),
 				},
 				DataReferenceIndex: 1,
 			},
@@ -594,7 +594,7 @@ func (track *InitTrack) marshal(w *mp4Writer) error {
 		_, err = w.writeBoxStart(&mp4.VisualSampleEntry{ // <mp4v>
 			SampleEntry: mp4.SampleEntry{
 				AnyTypeBox: mp4.AnyTypeBox{
-					Type: BoxTypeMp4v(),
+					Type: mp4.BoxTypeMp4v(),
 				},
 				DataReferenceIndex: 1,
 			},
@@ -771,7 +771,7 @@ func (track *InitTrack) marshal(w *mp4Writer) error {
 		_, err = w.writeBoxStart(&mp4.AudioSampleEntry{ // <ac-3>
 			SampleEntry: mp4.SampleEntry{
 				AnyTypeBox: mp4.AnyTypeBox{
-					Type: BoxTypeAC3(),
+					Type: mp4.BoxTypeAC3(),
 				},
 				DataReferenceIndex: 1,
 			},
@@ -783,7 +783,7 @@ func (track *InitTrack) marshal(w *mp4Writer) error {
 			return err
 		}
 
-		_, err = w.writeBox(&Dac3{ // <dac3/>
+		_, err = w.writeBox(&mp4.Dac3{ // <dac3/>
 			Fscod: codec.Fscod,
 			Bsid:  codec.Bsid,
 			Bsmod: codec.Bsmod,