Added ability to offset sample numbers on packetizers

audio/packetizer/adts.go

@@ -41,6 +41,10 @@ func (p *AdtsPacket) GetData() (result []byte) {
 	return
 }
 
+func (p *AdtsPacket) GetDataOffset(offset int64) []byte {
+	return p.GetData()
+}
+
 func NewAdtsPacketizer(reader io.Reader) *AdtsPacketizer {
 	return &AdtsPacketizer{reader: bufio.NewReader(reader)}
 }

audio/packetizer/flac.go

@@ -38,6 +38,10 @@ func (p *FLACPacket) GetData() []byte {
 	return p.data
 }
 
+func (p *FLACPacket) GetDataOffset(offset int64) []byte {
+	return p.GetData()
+}
+
 func (p *FLACPacket) Category() int64 {
 	return 0
 }

audio/packetizer/mp3.go

@@ -36,6 +36,10 @@ func (p *Mp3Packet) GetData() []byte {
 	return p.frame.Bytes()
 }
 
+func (p *Mp3Packet) GetDataOffset(offset int64) []byte {
+	return p.GetData()
+}
+
 func NewMp3Packetizer(reader io.Reader) *Mp3Packetizer {
 	return &Mp3Packetizer{decoder: mp3parser.NewDecoder(bufio.NewReader(reader))}
 }

audio/packetizer/ogg.go

@@ -60,6 +60,23 @@ func (p *OggPacket) GetData() []byte {
 	return buf.Bytes()
 }
 
+func (p *OggPacket) GetDataOffset(offset int64) []byte {
+	buf := bytes.NewBuffer(make([]byte, 0, 4+1+1+8+4+4+4+1+int(p.header.PageSegments)*(255+1)))
+
+	headerClone := p.header
+	headerClone.AbsoluteGranulePosition -= offset
+
+	binary.Write(buf, binary.LittleEndian, headerClone)
+	binary.Write(buf, binary.LittleEndian, p.pageSegmentTable)
+	for _, segment := range p.segments {
+		if len(segment) > 0 {
+			binary.Write(buf, binary.LittleEndian, segment)
+		}
+	}
+
+	return buf.Bytes()
+}
+
 func NewOggPacketizer(reader io.Reader) *OggPacketizer {
 	return &OggPacketizer{reader: bufio.NewReader(reader)}
 }

audio/packetizer/packetizer.go

@@ -18,6 +18,11 @@ type Packet interface {
 	GetData() []byte
 }
 
+type OffsetablePacket interface {
+	Packet
+	GetDataOffset(offset int64) []byte
+}
+
 type Packetizer interface {
 	GetPacket() Packet
 }