/* NAME mpegts.go - provides a data structure intended to encapsulate the properties of an MPEG-TS packet and also functions to allow manipulation of these packets. DESCRIPTION See Readme.md AUTHOR Saxon A. Nelson-Milton LICENSE mpegts.go is Copyright (C) 2017 the Australian Ocean Lab (AusOcean) It is free software: you can redistribute it and/or modify them under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with revid in gpl.txt. If not, see [GNU licenses](http://www.gnu.org/licenses). */ // Package mts provides MPEGT-TS (mts) encoding and related functions. package mts import ( "errors" "fmt" "github.com/Comcast/gots/packet" "github.com/Comcast/gots/pes" ) const PacketSize = 188 // Program ID for various types of ts packets. const ( SdtPid = 17 PatPid = 0 PmtPid = 4096 VideoPid = 256 ) // StreamID is the id of the first stream. const StreamID = 0xe0 // HeadSize is the size of an MPEG-TS packet header. const HeadSize = 4 // Consts relating to adaptation field. const ( AdaptationIdx = 4 // Index to the adaptation field (index of AFL). AdaptationControlIdx = 3 // Index to octet with adaptation field control. AdaptationFieldsIdx = AdaptationIdx + 1 // Adaptation field index is the index of the adaptation fields. DefaultAdaptationSize = 2 // Default size of the adaptation field. AdaptationControlMask = 0x30 // Mask for the adaptation field control in octet 3. DefaultAdaptationBodySize = 1 // Default size of the adaptation field body. DiscontinuityIndicatorMask = 0x80 // Mask for the discontinuity indicator at the discontinuity indicator idk. DiscontinuityIndicatorIdx = AdaptationIdx + 1 // The index at which the discontinuity indicator is found in an MTS packet. ) // TODO: make this better - currently doesn't make sense. const ( HasPayload = 0x1 HasAdaptationField = 0x2 ) /* Packet encapsulates the fields of an MPEG-TS packet. Below is the formatting of an MPEG-TS packet for reference! MPEG-TS Packet Formatting ============================================================================ | octet no | bit 0 | bit 1 | bit 2 | bit 3 | bit 4 | bit 5 | bit 6 | bit 7 | ============================================================================ | octet 0 | sync byte (0x47) | ---------------------------------------------------------------------------- | octet 1 | TEI | PUSI | Prior | PID | ---------------------------------------------------------------------------- | octet 2 | PID cont. | ---------------------------------------------------------------------------- | octet 3 | TSC | AFC | CC | ---------------------------------------------------------------------------- | octet 4 | AFL | ---------------------------------------------------------------------------- | octet 5 | DI | RAI | ESPI | PCRF | OPCRF | SPF | TPDF | AFEF | ---------------------------------------------------------------------------- | optional | PCR (48 bits => 6 bytes) | ---------------------------------------------------------------------------- | - | PCR cont. | ---------------------------------------------------------------------------- | - | PCR cont. | ---------------------------------------------------------------------------- | - | PCR cont. | ---------------------------------------------------------------------------- | - | PCR cont. | ---------------------------------------------------------------------------- | - | PCR cont. | ---------------------------------------------------------------------------- | optional | OPCR (48 bits => 6 bytes) | ---------------------------------------------------------------------------- | - | OPCR cont. | ---------------------------------------------------------------------------- | - | OPCR cont. | ---------------------------------------------------------------------------- | - | OPCR cont. | ---------------------------------------------------------------------------- | - | OPCR cont. | ---------------------------------------------------------------------------- | - | OPCR cont. | ---------------------------------------------------------------------------- | optional | SC | ---------------------------------------------------------------------------- | optional | TPDL | ---------------------------------------------------------------------------- | optional | TPD (variable length) | ---------------------------------------------------------------------------- | - | ... | ---------------------------------------------------------------------------- | optional | Extension (variable length) | ---------------------------------------------------------------------------- | - | ... | ---------------------------------------------------------------------------- | optional | Stuffing (variable length) | ---------------------------------------------------------------------------- | - | ... | ---------------------------------------------------------------------------- | optional | Payload (variable length) | ---------------------------------------------------------------------------- | - | ... | ---------------------------------------------------------------------------- */ type Packet struct { TEI bool // Transport Error Indicator PUSI bool // Payload Unit Start Indicator Priority bool // Tranposrt priority indicator PID uint16 // Packet identifier TSC byte // Transport Scrambling Control AFC byte // Adaption Field Control CC byte // Continuity Counter DI bool // Discontinouty indicator RAI bool // random access indicator ESPI bool // Elementary stream priority indicator PCRF bool // PCR flag OPCRF bool // OPCR flag SPF bool // Splicing point flag TPDF bool // Transport private data flag AFEF bool // Adaptation field extension flag PCR uint64 // Program clock reference OPCR uint64 // Original program clock reference SC byte // Splice countdown TPDL byte // Tranposrt private data length TPD []byte // Private data Ext []byte // Adaptation field extension Payload []byte // Mpeg ts Payload } // FindPmt will take a clip of MPEG-TS and try to find a PMT table - if one // is found, then it is returned along with its index, otherwise nil, -1 and an error is returned. func FindPmt(d []byte) ([]byte, int, error) { return FindPid(d, PmtPid) } // FindPat will take a clip of MPEG-TS and try to find a PAT table - if one // is found, then it is returned along with its index, otherwise nil, -1 and an error is returned. func FindPat(d []byte) ([]byte, int, error) { return FindPid(d, PatPid) } // FindPid will take a clip of MPEG-TS and try to find a packet with given PID - if one // is found, then it is returned along with its index, otherwise nil, -1 and an error is returned. func FindPid(d []byte, pid uint16) (pkt []byte, i int, err error) { if len(d) < PacketSize { return nil, -1, errors.New("MPEG-TS data not of valid length") } for i = 0; i < len(d); i += PacketSize { p := (uint16(d[i+1]&0x1f) << 8) | uint16(d[i+2]) if p == pid { pkt = d[i : i+PacketSize] return } } return nil, -1, fmt.Errorf("could not find packet with pid: %d", pid) } // FillPayload takes a channel and fills the packets Payload field until the // channel is empty or we've the packet reaches capacity func (p *Packet) FillPayload(data []byte) int { currentPktLen := 6 + asInt(p.PCRF)*6 if len(data) > PacketSize-currentPktLen { p.Payload = make([]byte, PacketSize-currentPktLen) } else { p.Payload = make([]byte, len(data)) } return copy(p.Payload, data) } // Bytes interprets the fields of the ts packet instance and outputs a // corresponding byte slice func (p *Packet) Bytes(buf []byte) []byte { if buf == nil || cap(buf) < PacketSize { buf = make([]byte, PacketSize) } if p.OPCRF { panic("original program clock reference field unsupported") } if p.SPF { panic("splicing countdown unsupported") } if p.TPDF { panic("transport private data unsupported") } if p.AFEF { panic("adaptation field extension unsupported") } buf = buf[:6] buf[0] = 0x47 buf[1] = (asByte(p.TEI)<<7 | asByte(p.PUSI)<<6 | asByte(p.Priority)<<5 | byte((p.PID&0xFF00)>>8)) buf[2] = byte(p.PID & 0x00FF) buf[3] = (p.TSC<<6 | p.AFC<<4 | p.CC) var maxPayloadSize int if p.AFC&0x2 != 0 { maxPayloadSize = PacketSize - 6 - asInt(p.PCRF)*6 } else { maxPayloadSize = PacketSize - 4 } stuffingLen := maxPayloadSize - len(p.Payload) if p.AFC&0x2 != 0 { buf[4] = byte(1 + stuffingLen + asInt(p.PCRF)*6) buf[5] = (asByte(p.DI)<<7 | asByte(p.RAI)<<6 | asByte(p.ESPI)<<5 | asByte(p.PCRF)<<4 | asByte(p.OPCRF)<<3 | asByte(p.SPF)<<2 | asByte(p.TPDF)<<1 | asByte(p.AFEF)) } else { buf = buf[:4] } for i := 40; p.PCRF && i >= 0; i -= 8 { buf = append(buf, byte((p.PCR<<15)>>uint(i))) } for i := 0; i < stuffingLen; i++ { buf = append(buf, 0xff) } curLen := len(buf) buf = buf[:PacketSize] copy(buf[curLen:], p.Payload) return buf } func asInt(b bool) int { if b { return 1 } return 0 } func asByte(b bool) byte { if b { return 1 } return 0 } type Option func(p *packet.Packet) // addAdaptationField adds an adaptation field to p, and applys the passed options to this field. // TODO: this will probably break if we already have adaptation field. func addAdaptationField(p *packet.Packet, options ...Option) error { if packet.ContainsAdaptationField((*packet.Packet)(p)) { return errors.New("Adaptation field is already present in packet") } // Create space for adaptation field. copy(p[HeadSize+DefaultAdaptationSize:], p[HeadSize:len(p)-DefaultAdaptationSize]) // TODO: seperate into own function // Update adaptation field control. p[AdaptationControlIdx] &= 0xff ^ AdaptationControlMask p[AdaptationControlIdx] |= AdaptationControlMask // Default the adaptationfield. resetAdaptation(p) // Apply and options that have bee passed. for _, option := range options { option(p) } return nil } // resetAdaptation sets fields in ps adaptation field to 0 if the adaptation field // exists, otherwise an error is returned. func resetAdaptation(p *packet.Packet) error { if !packet.ContainsAdaptationField((*packet.Packet)(p)) { return errors.New("No adaptation field in this packet") } p[AdaptationIdx] = DefaultAdaptationBodySize p[AdaptationIdx+1] = 0x00 return nil } // DiscontinuityIndicator returns and Option that will set p's discontinuity // indicator according to f. func DiscontinuityIndicator(f bool) Option { return func(p *packet.Packet) { set := byte(DiscontinuityIndicatorMask) if !f { set = 0x00 } p[DiscontinuityIndicatorIdx] &= 0xff ^ DiscontinuityIndicatorMask p[DiscontinuityIndicatorIdx] |= DiscontinuityIndicatorMask & set } } // GetPTSRange retreives the first and last PTS of an MPEGTS clip. func GetPTSRange(clip []byte, pid uint16) (pts [2]uint64, err error) { // Find the first packet with PID pidType. pkt, _, err := FindPid(clip, pid) if err != nil { return [2]uint64{}, err } // Get the payload of the packet, which will be the start of the PES packet. var _pkt packet.Packet copy(_pkt[:], pkt) payload, err := packet.Payload(&_pkt) if err != nil { fmt.Printf("_pkt: %v\n", _pkt) return [2]uint64{}, err } // Get the the first PTS from the PES header. _pes, err := pes.NewPESHeader(payload) if err != nil { return [2]uint64{}, err } pts[0] = _pes.PTS() // Get the final PTS searching from end of clip for access unit start. for i := len(clip) - PacketSize; i >= 0; i -= PacketSize { copy(_pkt[:], clip[i:i+PacketSize]) if packet.PayloadUnitStartIndicator(&_pkt) && uint16(_pkt.PID()) == pid { payload, err = packet.Payload(&_pkt) if err != nil { return [2]uint64{}, err } _pes, err = pes.NewPESHeader(payload) if err != nil { return [2]uint64{}, err } pts[1] = _pes.PTS() return } } return [2]uint64{}, errors.New("could only find one access unit in mpegts clip") }