Caption support (#2462)

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

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

@@ -0,0 +1,117 @@
+package astits
+
+import (
+	"fmt"
+
+	"github.com/asticode/go-astikit"
+)
+
+// PIDs
+const (
+	PIDPAT  uint16 = 0x0    // Program Association Table (PAT) contains a directory listing of all Program Map Tables.
+	PIDCAT  uint16 = 0x1    // Conditional Access Table (CAT) contains a directory listing of all ITU-T Rec. H.222 entitlement management message streams used by Program Map Tables.
+	PIDTSDT uint16 = 0x2    // Transport Stream Description Table (TSDT) contains descriptors related to the overall transport stream
+	PIDNull uint16 = 0x1fff // Null Packet (used for fixed bandwidth padding)
+)
+
+// DemuxerData represents a data parsed by Demuxer
+type DemuxerData struct {
+	EIT         *EITData
+	FirstPacket *Packet
+	NIT         *NITData
+	PAT         *PATData
+	PES         *PESData
+	PID         uint16
+	PMT         *PMTData
+	SDT         *SDTData
+	TOT         *TOTData
+}
+
+// MuxerData represents a data to be written by Muxer
+type MuxerData struct {
+	PID             uint16
+	AdaptationField *PacketAdaptationField
+	PES             *PESData
+}
+
+// parseData parses a payload spanning over multiple packets and returns a set of data
+func parseData(ps []*Packet, prs PacketsParser, pm programMap) (ds []*DemuxerData, err error) {
+	// Use custom parser first
+	if prs != nil {
+		var skip bool
+		if ds, skip, err = prs(ps); err != nil {
+			err = fmt.Errorf("astits: custom packets parsing failed: %w", err)
+			return
+		} else if skip {
+			return
+		}
+	}
+
+	// Get payload length
+	var l int
+	for _, p := range ps {
+		l += len(p.Payload)
+	}
+
+	// Append payload
+	var payload = make([]byte, l)
+	var c int
+	for _, p := range ps {
+		c += copy(payload[c:], p.Payload)
+	}
+
+	// Create reader
+	i := astikit.NewBytesIterator(payload)
+
+	// Parse PID
+	pid := ps[0].Header.PID
+
+	// Parse payload
+	if pid == PIDCAT {
+		// Information in a CAT payload is private and dependent on the CA system. Use the PacketsParser
+		// to parse this type of payload
+	} else if isPSIPayload(pid, pm) {
+		// Parse PSI data
+		var psiData *PSIData
+		if psiData, err = parsePSIData(i); err != nil {
+			err = fmt.Errorf("astits: parsing PSI data failed: %w", err)
+			return
+		}
+
+		// Append data
+		ds = psiData.toData(ps[0], pid)
+	} else if isPESPayload(payload) {
+		// Parse PES data
+		var pesData *PESData
+		if pesData, err = parsePESData(i); err != nil {
+			err = fmt.Errorf("astits: parsing PES data failed: %w", err)
+			return
+		}
+
+		// Append data
+		ds = append(ds, &DemuxerData{
+			FirstPacket: ps[0],
+			PES:         pesData,
+			PID:         pid,
+		})
+	}
+	return
+}
+
+// isPSIPayload checks whether the payload is a PSI one
+func isPSIPayload(pid uint16, pm programMap) bool {
+	return pid == PIDPAT || // PAT
+		pm.exists(pid) || // PMT
+		((pid >= 0x10 && pid <= 0x14) || (pid >= 0x1e && pid <= 0x1f)) //DVB
+}
+
+// isPESPayload checks whether the payload is a PES one
+func isPESPayload(i []byte) bool {
+	// Packet is not big enough
+	if len(i) < 3 {
+		return false
+	}
+
+	// Check prefix
+	return uint32(i[0])<<16|uint32(i[1])<<8|uint32(i[2]) == 1
+}