Caption support (#2462)

Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

vendor/github.com/asticode/go-astits/program_map.go

@@ -0,0 +1,57 @@
+package astits
+
+import "sync"
+
+// programMap represents a program ids map
+type programMap struct {
+	m *sync.Mutex
+	p map[uint16]uint16 // map[ProgramMapID]ProgramNumber
+}
+
+// newProgramMap creates a new program ids map
+func newProgramMap() programMap {
+	return programMap{
+		m: &sync.Mutex{},
+		p: make(map[uint16]uint16),
+	}
+}
+
+// exists checks whether the program with this pid exists
+func (m programMap) exists(pid uint16) (ok bool) {
+	m.m.Lock()
+	defer m.m.Unlock()
+	_, ok = m.p[pid]
+	return
+}
+
+// set sets a new program id
+func (m programMap) set(pid, number uint16) {
+	m.m.Lock()
+	defer m.m.Unlock()
+	m.p[pid] = number
+}
+
+func (m programMap) unset(pid uint16) {
+	m.m.Lock()
+	defer m.m.Unlock()
+	delete(m.p, pid)
+}
+
+func (m programMap) toPATData() *PATData {
+	m.m.Lock()
+	defer m.m.Unlock()
+
+	d := &PATData{
+		Programs:          []*PATProgram{},
+		TransportStreamID: uint16(PSITableIDPAT),
+	}
+
+	for pid, pnr := range m.p {
+		d.Programs = append(d.Programs, &PATProgram{
+			ProgramMapID:  pid,
+			ProgramNumber: pnr,
+		})
+	}
+
+	return d
+}