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TsPacket.go
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TsPacket.go
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package main
// TSPacket represents a single MPEG Transport Stream packet
// It holds pointers to each part of the packet, to reduce copying
// The Comment field is used to mark errors in the packet etc
type TsPacket struct {
Header *TsPacketHeader
AdaptationField *AdaptationField `json:"adaptation_field"`
Payload []byte `json:"data_byte"`
Comment string // can be used for logging, don't use newlines
bytes []byte // the raw packet bytes
}
func NewTsPacket(data []byte) TsPacket {
hdr := NewTsPacketHeader(data)
af := NewAdaptationField(data)
// copy the data, don't reuse the backing array
// otherwise you will get a race!
payld := append([]byte(nil), data[4+af.Length:]...)
bytes := append([]byte(nil), data...)
return TsPacket{
Header: hdr,
AdaptationField: af,
Payload: payld,
bytes: bytes,
}
}
// Represents the 4-byte transport stream packet header
// See ISO 13818-1 Table 2-2
type TsPacketHeader struct {
SyncByte byte `json:"sync_byte"`
Tei bool `json:"transport_error_indicator"`
Pusi bool `json:"payload_unit_start_indicator"`
Tp bool `json:"transport_priority"`
Pid int `json:"PID"`
Tsc byte `json:"transport_scrambling_control"`
Afc byte `json:"adaptation_field_control"`
Cc byte `json:"continuity_counter"`
}
// Constructor to create a new TS header struct
// expects data to start with a sync byte
func NewTsPacketHeader(data []byte) *TsPacketHeader {
return &TsPacketHeader{
SyncByte: data[0],
Tei: data[1]&128 != 0,
Pusi: data[1]&64 != 0,
Tp: data[1]&32 != 0,
Pid: ((int(data[1]) & 31) << 8) + int(data[2]),
Tsc: (data[3] & 192) >> 6,
Afc: (data[3] & 48) >> 4,
Cc: data[3] & 15,
}
}
// represents the optional adaptation field
// see ISO 13818-1 Table 2-6
type AdaptationField struct {
Length byte `json:"adaptation_field_length"`
Di bool `json:"discontinuity_indicator"`
Rai bool `json:"random_access_indicator"`
Espi bool `json:"elementary_stream_priority_indicator"`
Pcrf bool `json:"PCR_flag"`
Opcrf bool `json:"OPCR_flag"`
Spf bool `json:"splicing_point_flag"`
Tpdf bool `json:"transport_private_data_flag"`
Afef bool `json:"adaptation_field_extension_flag"`
//if PCR flag == 1
Pcrb int64 `json:"program_clock_reference_base"`
Pcre int64 `json:"program_clock_reference_extension"`
//if OPCR flag == 1
Opcrb int64 `json:"original_program_clock_reference_base"`
Opcre int64 `json:"original_program_clock_reference_extension"`
//if splicing_point_flag == 1
Sc byte `json:"splice_countdown"`
//if transport_private_data_flag == 1
Tpdl byte `json:"transport_private_data_length"`
Tpd []byte `json:"private_data_byte"`
//if adaptation_field_extension_flag == 1
Afel byte `json:"adaptation_field_extension_length"`
Ltwf bool `json:"ltw_flag"`
Pwrf bool `json:"piecewise_rate_flag"`
Ssf bool `json:"seamless_splice_flag"`
//if ltw_flag == 1
Ltwvf bool `json:"ltw_valid_flag"`
Ltwo int `json:"ltw_offset"`
//if piecewise_rate_flag == 1
Pwr int `json:"piecewise_rate"`
//if seamless_splice_flag == 1
St int `json:"splice_type"`
Dna int64 `json:"DTS_next_AU"`
}
// Constructor to create a new adaptation field struct
// expects data to start with a sync byte
// If AF is not present in the provided TS packet,
// returns zero struct if no af (Length = 0).
func NewAdaptationField(data []byte) *AdaptationField {
af := AdaptationField{}
if (data[3] & 32) == 0 {
//no af
return &af
}
if data[4] == 0 {
//zero length af
return &af
}
if len(data) >= 6 {
af.Length = data[4]
af.Di = data[5]&128 != 0
af.Rai = data[5]&64 != 0
af.Espi = data[5]&32 != 0
af.Pcrf = data[5]&16 != 0
af.Opcrf = data[5]&8 != 0
af.Spf = data[5]&4 != 0
af.Tpdf = data[5]&2 != 0
af.Afef = data[5]&1 != 0
}
//keep track of byte offset depending on flags
ofs := 6
if af.Pcrf {
if ofs+5 < len(data) {
af.Pcrb = 0
af.Pcrb += int64(data[ofs]) << 25
af.Pcrb += int64(data[ofs+1]) << 17
af.Pcrb += int64(data[ofs+2]) << 9
af.Pcrb += int64(data[ofs+3]) << 1
af.Pcrb += int64(data[ofs+4] >> 7)
af.Pcre = int64(data[ofs+4]&1) << 9
af.Pcre += int64(data[ofs+5])
}
ofs += 6
}
if af.Opcrf {
if ofs+5 < len(data) {
af.Opcrb = 0
af.Opcrb += int64(data[ofs]) << 25
af.Opcrb += int64(data[ofs+1]) << 17
af.Opcrb += int64(data[ofs+2]) << 9
af.Opcrb += int64(data[ofs+3]) << 1
af.Opcrb += int64(data[ofs+4] >> 7)
af.Opcre = int64(data[ofs+4]&1) << 9
af.Opcre += int64(data[ofs+5])
}
ofs += 6
}
if af.Spf {
if ofs < len(data) {
af.Sc = data[ofs]
}
ofs += 1
}
if af.Tpdf {
if ofs < len(data) {
af.Tpdl = data[ofs]
if ofs+int(af.Tpdl)+1 < len(data) {
af.Tpd = data[ofs+1 : ofs+int(af.Tpdl)+1]
}
}
ofs += int(af.Tpdl + 1)
}
if af.Afef {
if ofs+1 < len(data) {
af.Afel = data[ofs]
ofs += 1
af.Ltwf = data[ofs]&128 != 0
af.Pwrf = data[ofs]&64 != 0
af.Ssf = data[ofs]&32 != 0
ofs += 1
}
// TODO add the extension fields
}
return &af
}