Caption support (#2462)

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

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

@@ -0,0 +1,101 @@
+package astits
+
+import (
+	"sort"
+	"sync"
+)
+
+// packetPool represents a pool of packets
+type packetPool struct {
+	b map[uint16][]*Packet // Indexed by PID
+	m *sync.Mutex
+}
+
+// newPacketPool creates a new packet pool
+func newPacketPool() *packetPool {
+	return &packetPool{
+		b: make(map[uint16][]*Packet),
+		m: &sync.Mutex{},
+	}
+}
+
+// add adds a new packet to the pool
+func (b *packetPool) add(p *Packet) (ps []*Packet) {
+	// Throw away packet if error indicator
+	if p.Header.TransportErrorIndicator {
+		return
+	}
+
+	// Throw away packets that don't have a payload until we figure out what we're going to do with them
+	// TODO figure out what we're going to do with them :D
+	if !p.Header.HasPayload {
+		return
+	}
+
+	// Lock
+	b.m.Lock()
+	defer b.m.Unlock()
+
+	// Init buffer
+	var mps []*Packet
+	var ok bool
+	if mps, ok = b.b[p.Header.PID]; !ok {
+		mps = []*Packet{}
+	}
+
+	// Empty buffer if we detect a discontinuity
+	if hasDiscontinuity(mps, p) {
+		mps = []*Packet{}
+	}
+
+	// Throw away packet if it's the same as the previous one
+	if isSameAsPrevious(mps, p) {
+		return
+	}
+
+	// Add packet
+	if len(mps) > 0 || (len(mps) == 0 && p.Header.PayloadUnitStartIndicator) {
+		mps = append(mps, p)
+	}
+
+	// Check payload unit start indicator
+	if p.Header.PayloadUnitStartIndicator && len(mps) > 1 {
+		ps = mps[:len(mps)-1]
+		mps = []*Packet{p}
+	}
+
+	// Assign
+	b.b[p.Header.PID] = mps
+	return
+}
+
+// dump dumps the packet pool by looking for the first item with packets inside
+func (b *packetPool) dump() (ps []*Packet) {
+	b.m.Lock()
+	defer b.m.Unlock()
+	var keys []int
+	for k := range b.b {
+		keys = append(keys, int(k))
+	}
+	sort.Ints(keys)
+	for _, k := range keys {
+		ps = b.b[uint16(k)]
+		delete(b.b, uint16(k))
+		if len(ps) > 0 {
+			return
+		}
+	}
+	return
+}
+
+// hasDiscontinuity checks whether a packet is discontinuous with a set of packets
+func hasDiscontinuity(ps []*Packet, p *Packet) bool {
+	return (p.Header.HasAdaptationField && p.AdaptationField.DiscontinuityIndicator) ||
+		(len(ps) > 0 && p.Header.HasPayload && p.Header.ContinuityCounter != (ps[len(ps)-1].Header.ContinuityCounter+1)%16) ||
+		(len(ps) > 0 && !p.Header.HasPayload && p.Header.ContinuityCounter != ps[len(ps)-1].Header.ContinuityCounter)
+}
+
+// isSameAsPrevious checks whether a packet is the same as the last packet of a set of packets
+func isSameAsPrevious(ps []*Packet, p *Packet) bool {
+	return len(ps) > 0 && p.Header.HasPayload && p.Header.ContinuityCounter == ps[len(ps)-1].Header.ContinuityCounter
+}