Add MP4 atoms reader

pkg/iso/atoms.go

@@ -260,6 +260,22 @@ func (m *Movie) WriteAudioTrack(id uint32, codec string, timescale uint32, chann
 	m.EndAtom() // TRAK
 }
 
+const (
+	TfhdDefaultSampleDuration = 0x000008
+	TfhdDefaultSampleSize     = 0x000010
+	TfhdDefaultSampleFlags    = 0x000020
+	TfhdDefaultBaseIsMoof     = 0x020000
+)
+
+const (
+	TrunDataOffset       = 0x000001
+	TrunFirstSampleFlags = 0x000004
+	TrunSampleDuration   = 0x0000100
+	TrunSampleSize       = 0x0000200
+	TrunSampleFlags      = 0x0000400
+	TrunSampleCTS        = 0x0000800
+)
+
 func (m *Movie) WriteMovieFragment(seq, tid, duration, size, flags uint32, time uint64) {
 	m.StartAtom(Moof)
 
@@ -271,13 +287,6 @@ func (m *Movie) WriteMovieFragment(seq, tid, duration, size, flags uint32, time
 
 	m.StartAtom(MoofTraf)
 
-	const (
-		TfhdDefaultSampleDuration = 0x000008
-		TfhdDefaultSampleSize     = 0x000010
-		TfhdDefaultSampleFlags    = 0x000020
-		TfhdDefaultBaseIsMoof     = 0x020000
-	)
-
 	m.StartAtom(MoofTrafTfhd)
 	m.Skip(1) // version
 	m.WriteUint24(
@@ -298,15 +307,6 @@ func (m *Movie) WriteMovieFragment(seq, tid, duration, size, flags uint32, time
 	m.WriteUint64(time) // base media decode time
 	m.EndAtom()
 
-	const (
-		TrunDataOffset       = 0x000001
-		TrunFirstSampleFlags = 0x000004
-		TrunSampleDuration   = 0x0000100
-		TrunSampleSize       = 0x0000200
-		TrunSampleFlags      = 0x0000400
-		TrunSampleCTS        = 0x0000800
-	)
-
 	m.StartAtom(MoofTrafTrun)
 	m.Skip(1)                     // version
 	m.WriteUint24(TrunDataOffset) // flags