Caption support (#2462)

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

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

@@ -0,0 +1,130 @@
+package astits
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/asticode/go-astikit"
+)
+
+// parseDVBTime parses a DVB time
+// This field is coded as 16 bits giving the 16 LSBs of MJD followed by 24 bits coded as 6 digits in 4 - bit Binary
+// Coded Decimal (BCD). If the start time is undefined (e.g. for an event in a NVOD reference service) all bits of the
+// field are set to "1".
+// I apologize for the computation which is really messy but details are given in the documentation
+// Page: 160 | Annex C | 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
+func parseDVBTime(i *astikit.BytesIterator) (t time.Time, err error) {
+	// Get next 2 bytes
+	var bs []byte
+	if bs, err = i.NextBytesNoCopy(2); err != nil {
+		err = fmt.Errorf("astits: fetching next bytes failed: %w", err)
+		return
+	}
+
+	// Date
+	var mjd = uint16(bs[0])<<8 | uint16(bs[1])
+	var yt = int((float64(mjd) - 15078.2) / 365.25)
+	var mt = int((float64(mjd) - 14956.1 - float64(int(float64(yt)*365.25))) / 30.6001)
+	var d = int(float64(mjd) - 14956 - float64(int(float64(yt)*365.25)) - float64(int(float64(mt)*30.6001)))
+	var k int
+	if mt == 14 || mt == 15 {
+		k = 1
+	}
+	var y = yt + k
+	var m = mt - 1 - k*12
+	t, _ = time.Parse("06-01-02", fmt.Sprintf("%d-%d-%d", y, m, d))
+
+	// Time
+	var s time.Duration
+	if s, err = parseDVBDurationSeconds(i); err != nil {
+		err = fmt.Errorf("astits: parsing DVB duration seconds failed: %w", err)
+		return
+	}
+	t = t.Add(s)
+	return
+}
+
+// parseDVBDurationMinutes parses a minutes duration
+// 16 bit field containing the duration of the event in hours, minutes. format: 4 digits, 4 - bit BCD = 18 bit
+func parseDVBDurationMinutes(i *astikit.BytesIterator) (d time.Duration, err error) {
+	var bs []byte
+	if bs, err = i.NextBytesNoCopy(2); err != nil {
+		err = fmt.Errorf("astits: fetching next bytes failed: %w", err)
+		return
+	}
+	d = parseDVBDurationByte(bs[0])*time.Hour + parseDVBDurationByte(bs[1])*time.Minute
+	return
+}
+
+// parseDVBDurationSeconds parses a seconds duration
+// 24 bit field containing the duration of the event in hours, minutes, seconds. format: 6 digits, 4 - bit BCD = 24 bit
+func parseDVBDurationSeconds(i *astikit.BytesIterator) (d time.Duration, err error) {
+	var bs []byte
+	if bs, err = i.NextBytesNoCopy(3); err != nil {
+		err = fmt.Errorf("astits: fetching next bytes failed: %w", err)
+		return
+	}
+	d = parseDVBDurationByte(bs[0])*time.Hour + parseDVBDurationByte(bs[1])*time.Minute + parseDVBDurationByte(bs[2])*time.Second
+	return
+}
+
+// parseDVBDurationByte parses a duration byte
+func parseDVBDurationByte(i byte) time.Duration {
+	return time.Duration(uint8(i)>>4*10 + uint8(i)&0xf)
+}
+
+func writeDVBTime(w *astikit.BitsWriter, t time.Time) (int, error) {
+	year := t.Year() - 1900
+	month := t.Month()
+	day := t.Day()
+
+	l := 0
+	if month <= time.February {
+		l = 1
+	}
+
+	mjd := 14956 + day + int(float64(year-l)*365.25) + int(float64(int(month)+1+l*12)*30.6001)
+
+	d := t.Sub(t.Truncate(24 * time.Hour))
+
+	b := astikit.NewBitsWriterBatch(w)
+
+	b.Write(uint16(mjd))
+	bytesWritten, err := writeDVBDurationSeconds(w, d)
+	if err != nil {
+		return 2, err
+	}
+
+	return bytesWritten + 2, b.Err()
+}
+
+func writeDVBDurationMinutes(w *astikit.BitsWriter, d time.Duration) (int, error) {
+	b := astikit.NewBitsWriterBatch(w)
+
+	hours := uint8(d.Hours())
+	minutes := uint8(int(d.Minutes()) % 60)
+
+	b.Write(dvbDurationByteRepresentation(hours))
+	b.Write(dvbDurationByteRepresentation(minutes))
+
+	return 2, b.Err()
+}
+
+func writeDVBDurationSeconds(w *astikit.BitsWriter, d time.Duration) (int, error) {
+	b := astikit.NewBitsWriterBatch(w)
+
+	hours := uint8(d.Hours())
+	minutes := uint8(int(d.Minutes()) % 60)
+	seconds := uint8(int(d.Seconds()) % 60)
+
+	b.Write(dvbDurationByteRepresentation(hours))
+	b.Write(dvbDurationByteRepresentation(minutes))
+	b.Write(dvbDurationByteRepresentation(seconds))
+
+	return 3, b.Err()
+}
+
+func dvbDurationByteRepresentation(n uint8) uint8 {
+	return (n/10)<<4 | n%10
+}