Use Items.Index in VTT write method

subtitles.go

@@ -6,6 +6,7 @@ import (
 	"math"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strconv"
 	"strings"
 	"time"
@@ -595,6 +596,76 @@ func (s *Subtitles) Order() {
 	}
 }
 
+// ClipFrom clip items from input time
+func (s *Subtitles) ClipFrom(cf time.Duration) {
+	newIndex := 0
+	var items []*Item
+	for index := 0; index < len(s.Items); index++ {
+		s.Items[index].StartAt -= cf
+		s.Items[index].EndAt -= cf
+		s.Items[index].Index = newIndex
+		if s.Items[index].StartAt < 0 {
+			s.Items[index].StartAt = 0
+		}
+		if s.Items[index].EndAt > 0 {
+			items = append(items, s.Items[index])
+		}
+	}
+	s.Items = items
+}
+
+func copy(source interface{}, destin interface{}) {
+	x := reflect.ValueOf(source)
+	if x.Kind() == reflect.Ptr {
+		starX := x.Elem()
+		y := reflect.New(starX.Type())
+		starY := y.Elem()
+		starY.Set(starX)
+		reflect.ValueOf(destin).Elem().Set(y.Elem())
+	}
+}
+
+// Clone subtitles
+func (s *Subtitles) Clone() *Subtitles {
+	sub := &Subtitles{}
+	copy(s.Metadata, sub.Metadata)
+	for k, r := range s.Regions {
+		copy(r, sub.Regions[k])
+	}
+	for k, r := range s.Styles {
+		copy(r, sub.Styles[k])
+	}
+	for i := 0; i < len(s.Items); i++ {
+		n := &Item{}
+		copy(s.Items[i], n)
+		sub.Items = append(sub.Items, n)
+	}
+	return sub
+}
+
+// ClipFrom clip items until input time
+func (s *Subtitles) ClipTo(ct time.Duration) {
+	lastIndex := 0
+	for index := 0; index < len(s.Items); index++ {
+		lastIndex = index
+		if s.Items[index].StartAt > ct {
+			break
+		}
+		if s.Items[index].EndAt > ct {
+			s.Items[index].EndAt = ct
+			break
+		}
+	}
+	s.Items = s.Items[:lastIndex+1]
+}
+
+// FixIndex fix item index
+func (s *Subtitles) FixIndex() {
+	for i := 0; i < len(s.Items); i++ {
+		s.Items[i].Index = i + 1
+	}
+}
+
 // RemoveStyling removes the styling from the subtitles
 func (s *Subtitles) RemoveStyling() {
 	s.Regions = map[string]*Region{}

subtitles_test.go

@@ -276,3 +276,29 @@ func TestSubtitles_RemoveStyling(t *testing.T) {
 		Styles:  map[string]*astisub.Style{},
 	}, s)
 }
+
+func TestSubtitles_FixIndex(t *testing.T) {
+	var s = mockSubtitles()
+	s.FixIndex()
+	for i := 0; i < len(s.Items); i++ {
+		assert.Equal(t, i+1, s.Items[i].Index)
+	}
+}
+
+func TestSubtitles_ClipTo(t *testing.T) {
+	var s = mockSubtitles()
+	s.ClipTo(2 * time.Second)
+	assert.Equal(t, 1, len(s.Items))
+	assert.Equal(t, 1*time.Second, s.Items[0].StartAt)
+	assert.Equal(t, 2*time.Second, s.Items[0].EndAt)
+}
+
+func TestSubtitles_ClipFrom(t *testing.T) {
+	var s = mockSubtitles()
+	s.ClipFrom(2 * time.Second)
+	assert.Equal(t, 2, len(s.Items))
+	assert.Equal(t, 0*time.Second, s.Items[0].StartAt)
+	assert.Equal(t, 1*time.Second, s.Items[0].EndAt)
+	assert.Equal(t, 1*time.Second, s.Items[1].StartAt)
+	assert.Equal(t, 5*time.Second, s.Items[1].EndAt)
+}

webvtt.go

@@ -277,7 +277,26 @@ func formatDurationWebVTT(i time.Duration) string {
 }
 
 // WriteToWebVTT writes subtitles in .vtt format
-func (s Subtitles) WriteToWebVTT(o io.Writer) (err error) {
+// if set true in second args write index as item index
+func (s Subtitles) WriteToWebVTT(args ...interface{}) (err error) {
+	var o io.Writer
+	writeWithIndex := false
+	for i, arg := range args {
+		switch i {
+		case 0: // default output writer
+			out, ok := arg.(io.Writer)
+			if !ok {
+				return fmt.Errorf("first input argument must be io.Writer")
+			}
+			o = out
+		case 1:
+			b, ok := arg.(bool)
+			if !ok {
+				return fmt.Errorf("second input argument must be boolean")
+			}
+			writeWithIndex = b
+		}
+	}
 	// Do not write anything if no subtitles
 	if len(s.Items) == 0 {
 		err = ErrNoSubtitlesToWrite
@@ -350,7 +369,11 @@ func (s Subtitles) WriteToWebVTT(o io.Writer) (err error) {
 		}
 
 		// Add time boundaries
-		c = append(c, []byte(strconv.Itoa(index+1))...)
+		if writeWithIndex {
+			c = append(c, []byte(strconv.Itoa(item.Index))...)
+		} else {
+			c = append(c, []byte(strconv.Itoa(index+1))...)
+		}
 		c = append(c, bytesLineSeparator...)
 		c = append(c, []byte(formatDurationWebVTT(item.StartAt))...)
 		c = append(c, bytesWebVTTTimeBoundariesSeparator...)