Caption support (#2462)

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

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

@@ -0,0 +1,63 @@
+package astits
+
+import (
+	"fmt"
+
+	"github.com/asticode/go-astikit"
+)
+
+const (
+	patSectionEntryBytesSize = 4 // 16 bits + 3 reserved + 13 bits = 32 bits
+)
+
+// PATData represents a PAT data
+// https://en.wikipedia.org/wiki/Program-specific_information
+type PATData struct {
+	Programs          []*PATProgram
+	TransportStreamID uint16
+}
+
+// PATProgram represents a PAT program
+type PATProgram struct {
+	ProgramMapID  uint16 // The packet identifier that contains the associated PMT
+	ProgramNumber uint16 // Relates to the Table ID extension in the associated PMT. A value of 0 is reserved for a NIT packet identifier.
+}
+
+// parsePATSection parses a PAT section
+func parsePATSection(i *astikit.BytesIterator, offsetSectionsEnd int, tableIDExtension uint16) (d *PATData, err error) {
+	// Create data
+	d = &PATData{TransportStreamID: tableIDExtension}
+
+	// Loop until end of section data is reached
+	for i.Offset() < offsetSectionsEnd {
+		// Get next bytes
+		var bs []byte
+		if bs, err = i.NextBytesNoCopy(4); err != nil {
+			err = fmt.Errorf("astits: fetching next bytes failed: %w", err)
+			return
+		}
+
+		// Append program
+		d.Programs = append(d.Programs, &PATProgram{
+			ProgramMapID:  uint16(bs[2]&0x1f)<<8 | uint16(bs[3]),
+			ProgramNumber: uint16(bs[0])<<8 | uint16(bs[1]),
+		})
+	}
+	return
+}
+
+func calcPATSectionLength(d *PATData) uint16 {
+	return uint16(4 * len(d.Programs))
+}
+
+func writePATSection(w *astikit.BitsWriter, d *PATData) (int, error) {
+	b := astikit.NewBitsWriterBatch(w)
+
+	for _, p := range d.Programs {
+		b.Write(p.ProgramNumber)
+		b.WriteN(uint8(0xff), 3)
+		b.WriteN(p.ProgramMapID, 13)
+	}
+
+	return len(d.Programs) * patSectionEntryBytesSize, b.Err()
+}