mirror of https://bitbucket.org/ausocean/av.git
111 lines
3.2 KiB
Go
111 lines
3.2 KiB
Go
/*
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NAME
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discontinuity.go
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DESCRIPTION
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discontinuity.go provides functionality for detecting discontinuities in
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mpegts and accounting for using the discontinuity indicator in the adaptation
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field.
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AUTHOR
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Saxon A. Nelson-Milton <saxon@ausocean.org>
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LICENSE
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discontinuity.go is Copyright (C) 2017-2019 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see [GNU licenses](http://www.gnu.org/licenses).
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*/
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package mts
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import "github.com/Comcast/gots/packet"
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// discontinuityRepairer provides function to detect discontinuities in mpegts
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// and set the discontinuity indicator as appropriate.
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type DiscontinuityRepairer struct {
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expCC map[int]int
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}
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// NewDiscontinuityRepairer returns a pointer to a new discontinuityRepairer.
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func NewDiscontinuityRepairer() *DiscontinuityRepairer {
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return &DiscontinuityRepairer{
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expCC: map[int]int{
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PatPid: 16,
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PmtPid: 16,
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VideoPid: 16,
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},
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}
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}
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// Failed is to be called in the case of a failed send. This will decrement the
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// expectedCC so that it aligns with the failed chunks cc.
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func (dr *DiscontinuityRepairer) Failed() {
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dr.decExpectedCC(PatPid)
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}
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// Repair takes a clip of mpegts and checks that the first packet, which should
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// be a PAT, contains a cc that is expected, otherwise the discontinuity indicator
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// is set to true.
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func (dr *DiscontinuityRepairer) Repair(d []byte) error {
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var pkt [PacketSize]byte
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copy(pkt[:], d[:PacketSize])
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p := (*packet.Packet)(&pkt)
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pid := p.PID()
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if pid != PatPid {
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panic("Clip to repair must have PAT first")
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}
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cc := p.ContinuityCounter()
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expect, exists := dr.expectedCC(pid)
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dr.incExpectedCC(pid)
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if !exists {
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dr.setExpectedCC(pid, cc)
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} else if cc != int(expect) {
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if packet.ContainsAdaptationField(p) {
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(*packet.AdaptationField)(p).SetDiscontinuity(true)
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} else {
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err := addAdaptationField(&pkt, DiscontinuityIndicator(true))
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if err != nil {
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return err
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}
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}
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dr.setExpectedCC(pid, cc)
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copy(d[:PacketSize], pkt[:])
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}
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return nil
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}
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// expectedCC returns the expected cc. If the cc hasn't been used yet, then 16
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// and false is returned.
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func (dr *DiscontinuityRepairer) expectedCC(pid int) (int, bool) {
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if dr.expCC[pid] == 16 {
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return 16, false
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}
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return dr.expCC[pid], true
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}
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// incExpectedCC increments the expected cc.
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func (dr *DiscontinuityRepairer) incExpectedCC(pid int) {
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dr.expCC[pid] = (dr.expCC[pid] + 1) & 0xf
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}
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// decExpectedCC decrements the expected cc.
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func (dr *DiscontinuityRepairer) decExpectedCC(pid int) {
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dr.expCC[pid] = (dr.expCC[pid] - 1) & 0xf
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}
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// setExpectedCC sets the expected cc.
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func (dr *DiscontinuityRepairer) setExpectedCC(pid, cc int) {
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dr.expCC[pid] = cc
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}
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