av/stream/mts/discontinuity.go

111 lines
3.2 KiB
Go

/*
NAME
discontinuity.go
DESCRIPTION
discontinuity.go provides functionality for detecting discontinuities in
mpegts and accounting for using the discontinuity indicator in the adaptation
field.
AUTHOR
Saxon A. Nelson-Milton <saxon@ausocean.org>
LICENSE
discontinuity.go is Copyright (C) 2017-2019 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
import "github.com/Comcast/gots/packet"
// discontinuityRepairer provides function to detect discontinuities in mpegts
// and set the discontinuity indicator as appropriate.
type DiscontinuityRepairer struct {
expCC map[int]int
}
// NewDiscontinuityRepairer returns a pointer to a new discontinuityRepairer.
func NewDiscontinuityRepairer() *DiscontinuityRepairer {
return &DiscontinuityRepairer{
expCC: map[int]int{
PatPid: 16,
PmtPid: 16,
VideoPid: 16,
},
}
}
// Failed is to be called in the case of a failed send. This will decrement the
// expectedCC so that it aligns with the failed chunks cc.
func (dr *DiscontinuityRepairer) Failed() {
dr.decExpectedCC(PatPid)
}
// Repair takes a clip of mpegts and checks that the first packet, which should
// be a PAT, contains a cc that is expected, otherwise the discontinuity indicator
// is set to true.
func (dr *DiscontinuityRepairer) Repair(d []byte) error {
var pkt [PacketSize]byte
copy(pkt[:], d[:PacketSize])
p := (*packet.Packet)(&pkt)
pid := p.PID()
if pid != PatPid {
panic("Clip to repair must have PAT first")
}
cc := p.ContinuityCounter()
expect, exists := dr.ExpectedCC(pid)
dr.IncExpectedCC(pid)
if !exists {
dr.SetExpectedCC(pid, cc)
} else if cc != int(expect) {
if packet.ContainsAdaptationField(p) {
(*packet.AdaptationField)(p).SetDiscontinuity(true)
} else {
err := addAdaptationField(&pkt, DiscontinuityIndicator(true))
if err != nil {
return err
}
}
dr.SetExpectedCC(pid, cc)
copy(d[:PacketSize], pkt[:])
}
return nil
}
// expectedCC returns the expected cc. If the cc hasn't been used yet, then 16
// and false is returned.
func (dr *DiscontinuityRepairer) ExpectedCC(pid int) (int, bool) {
if dr.expCC[pid] == 16 {
return 16, false
}
return dr.expCC[pid], true
}
// incExpectedCC increments the expected cc.
func (dr *DiscontinuityRepairer) IncExpectedCC(pid int) {
dr.expCC[pid] = (dr.expCC[pid] + 1) & 0xf
}
// decExpectedCC decrements the expected cc.
func (dr *DiscontinuityRepairer) decExpectedCC(pid int) {
dr.expCC[pid] = (dr.expCC[pid] - 1) & 0xf
}
// setExpectedCC sets the expected cc.
func (dr *DiscontinuityRepairer) SetExpectedCC(pid, cc int) {
dr.expCC[pid] = cc
}