pat.go

package mpeg2ts

import (
	"fmt"
)

// Program Association Table
type PAT struct {
	Pointer                byte
	TableID                byte
	SectionSyntaxIndicator bool
	Reserved1              byte
	SectionLength          uint16
	TransportStreamID      uint16
	Reserved2              int
	Version                byte
	CurrentNextIndicator   bool
	SectionNumber          byte
	LastSectionNumber      byte
	CRC32                  uint
	Programs               []PATProgram
}

type PATProgram struct {
	ProgramNumber uint16
	Reserved      int
	NetworkPID    PID
	ProgramMapPID PID
}

func (p *Packet) ParsePAT() (PAT, error) {
	pat := PAT{}
	payload, err := p.GetPayload()
	if err != nil {
		return PAT{}, err
	}
	pat.Pointer = payload[0]
	pat.TableID = payload[1]
	pat.SectionSyntaxIndicator = ((payload[2] >> 7) & 0x01) == 1
	if ((payload[2] >> 6) & 0x01) == 1 {
		return PAT{}, fmt.Errorf("invalid format")
	}
	pat.SectionLength = uint16(payload[2]&0x0F)<<8 | uint16(payload[3])
	pat.TransportStreamID = uint16(payload[4])<<8 | uint16(payload[5])
	pat.Version = (payload[6] >> 1) & 0x1F
	pat.CurrentNextIndicator = (payload[6] & 0x01) == 0x01
	pat.SectionNumber = payload[7]
	pat.LastSectionNumber = payload[8]

	pat.Programs = make([]PATProgram, (pat.SectionLength-5-4)/4)
	for i := uint16(0); i < (pat.SectionLength-5-4)/4; i++ {
		base := 9 + i*4
		pat.Programs[i].ProgramNumber = uint16(payload[base])<<8 | uint16(payload[base+1])
		if pat.Programs[i].ProgramNumber == 0x0000 {
			pat.Programs[i].NetworkPID = PID(uint16(payload[base+2]&0x1f)<<8 | uint16(payload[base+3])&0x1fff)
		} else {
			pat.Programs[i].ProgramMapPID = PID(uint16(payload[base+2]&0x1f)<<8 | uint16(payload[base+3])&0x1fff)
		}
	}
	pat.CRC32 = uint(payload[pat.SectionLength])<<24 | uint(payload[pat.SectionLength+1])<<16 | uint(payload[pat.SectionLength+2])<<8 | uint(payload[pat.SectionLength+3])

	crc := calculateCRC(payload[1:pat.SectionLength])
	if uint32(pat.CRC32) != crc {
		return PAT{}, fmt.Errorf("CRC32 mismatch")
	}

	// fmt.Println("CRC OK")
	return pat, nil
}