Caption support (#2462)

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

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

@@ -0,0 +1,108 @@
+package astits
+
+import (
+	"fmt"
+
+	"github.com/asticode/go-astikit"
+)
+
+// Running statuses
+const (
+	RunningStatusNotRunning          = 1
+	RunningStatusPausing             = 3
+	RunningStatusRunning             = 4
+	RunningStatusServiceOffAir       = 5
+	RunningStatusStartsInAFewSeconds = 2
+	RunningStatusUndefined           = 0
+)
+
+// SDTData represents an SDT data
+// Page: 33 | Chapter: 5.2.3 | Link: https://www.dvb.org/resources/public/standards/a38_dvb-si_specification.pdf
+// (barbashov) the link above can be broken, alternative: https://dvb.org/wp-content/uploads/2019/12/a038_tm1217r37_en300468v1_17_1_-_rev-134_-_si_specification.pdf
+type SDTData struct {
+	OriginalNetworkID uint16
+	Services          []*SDTDataService
+	TransportStreamID uint16
+}
+
+// SDTDataService represents an SDT data service
+type SDTDataService struct {
+	Descriptors            []*Descriptor
+	HasEITPresentFollowing bool // When true indicates that EIT present/following information for the service is present in the current TS
+	HasEITSchedule         bool // When true indicates that EIT schedule information for the service is present in the current TS
+	HasFreeCSAMode         bool // When true indicates that access to one or more streams may be controlled by a CA system.
+	RunningStatus          uint8
+	ServiceID              uint16
+}
+
+// parseSDTSection parses an SDT section
+func parseSDTSection(i *astikit.BytesIterator, offsetSectionsEnd int, tableIDExtension uint16) (d *SDTData, err error) {
+	// Create data
+	d = &SDTData{TransportStreamID: tableIDExtension}
+
+	// Get next bytes
+	var bs []byte
+	if bs, err = i.NextBytesNoCopy(2); err != nil {
+		err = fmt.Errorf("astits: fetching next bytes failed: %w", err)
+		return
+	}
+
+	// Original network ID
+	d.OriginalNetworkID = uint16(bs[0])<<8 | uint16(bs[1])
+
+	// Reserved for future use
+	i.Skip(1)
+
+	// Loop until end of section data is reached
+	for i.Offset() < offsetSectionsEnd {
+		// Create service
+		s := &SDTDataService{}
+
+		// Get next bytes
+		if bs, err = i.NextBytesNoCopy(2); err != nil {
+			err = fmt.Errorf("astits: fetching next bytes failed: %w", err)
+			return
+		}
+
+		// Service ID
+		s.ServiceID = uint16(bs[0])<<8 | uint16(bs[1])
+
+		// Get next byte
+		var b byte
+		if b, err = i.NextByte(); err != nil {
+			err = fmt.Errorf("astits: fetching next byte failed: %w", err)
+			return
+		}
+
+		// EIT schedule flag
+		s.HasEITSchedule = uint8(b&0x2) > 0
+
+		// EIT present/following flag
+		s.HasEITPresentFollowing = uint8(b&0x1) > 0
+
+		// Get next byte
+		if b, err = i.NextByte(); err != nil {
+			err = fmt.Errorf("astits: fetching next byte failed: %w", err)
+			return
+		}
+
+		// Running status
+		s.RunningStatus = uint8(b) >> 5
+
+		// Free CA mode
+		s.HasFreeCSAMode = uint8(b&0x10) > 0
+
+		// We need to rewind since the current byte is used by the descriptor as well
+		i.Skip(-1)
+
+		// Descriptors
+		if s.Descriptors, err = parseDescriptors(i); err != nil {
+			err = fmt.Errorf("astits: parsing descriptors failed: %w", err)
+			return
+		}
+
+		// Append service
+		d.Services = append(d.Services, s)
+	}
+	return
+}