Caption support (#2462)

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

vendor/github.com/asticode/go-astisub/srt.go

@@ -0,0 +1,159 @@
+package astisub
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Constants
+const (
+	srtTimeBoundariesSeparator = " --> "
+)
+
+// Vars
+var (
+	bytesSRTTimeBoundariesSeparator = []byte(srtTimeBoundariesSeparator)
+)
+
+// parseDurationSRT parses an .srt duration
+func parseDurationSRT(i string) (time.Duration, error) {
+	return parseDuration(i, ",", 3)
+}
+
+// ReadFromSRT parses an .srt content
+func ReadFromSRT(i io.Reader) (o *Subtitles, err error) {
+	// Init
+	o = NewSubtitles()
+	var scanner = bufio.NewScanner(i)
+
+	// Scan
+	var line string
+	var lineNum int
+	var s = &Item{}
+	for scanner.Scan() {
+		// Fetch line
+		line = strings.TrimSpace(scanner.Text())
+		lineNum++
+
+		// Remove BOM header
+		if lineNum == 1 {
+			line = strings.TrimPrefix(line, string(BytesBOM))
+		}
+
+		// Line contains time boundaries
+		if strings.Contains(line, srtTimeBoundariesSeparator) {
+			// Return the wrong number of rows
+			if len(s.Lines) == 0 {
+				err = fmt.Errorf("astisub: line %d: no lines", lineNum)
+				return
+			}
+
+			// Remove last item of previous subtitle since it's the index
+			index := s.Lines[len(s.Lines)-1]
+			s.Lines = s.Lines[:len(s.Lines)-1]
+
+			// Remove trailing empty lines
+			if len(s.Lines) > 0 {
+				for i := len(s.Lines) - 1; i >= 0; i-- {
+					if len(s.Lines[i].Items) > 0 {
+						for j := len(s.Lines[i].Items) - 1; j >= 0; j-- {
+							if len(s.Lines[i].Items[j].Text) == 0 {
+								s.Lines[i].Items = s.Lines[i].Items[:j]
+							} else {
+								break
+							}
+						}
+						if len(s.Lines[i].Items) == 0 {
+							s.Lines = s.Lines[:i]
+						}
+
+					}
+				}
+			}
+
+			// Init subtitle
+			s = &Item{}
+
+			// Fetch Index
+			s.Index, _ = strconv.Atoi(index.String())
+
+			// Extract time boundaries
+			s1 := strings.Split(line, srtTimeBoundariesSeparator)
+			if l := len(s1); l < 2 {
+				err = fmt.Errorf("astisub: line %d: time boundaries has only %d element(s)", lineNum, l)
+				return
+			}
+			// We do this to eliminate extra stuff like positions which are not documented anywhere
+			s2 := strings.Split(s1[1], " ")
+
+			// Parse time boundaries
+			if s.StartAt, err = parseDurationSRT(s1[0]); err != nil {
+				err = fmt.Errorf("astisub: line %d: parsing srt duration %s failed: %w", lineNum, s1[0], err)
+				return
+			}
+			if s.EndAt, err = parseDurationSRT(s2[0]); err != nil {
+				err = fmt.Errorf("astisub: line %d: parsing srt duration %s failed: %w", lineNum, s2[0], err)
+				return
+			}
+
+			// Append subtitle
+			o.Items = append(o.Items, s)
+		} else {
+			// Add text
+			s.Lines = append(s.Lines, Line{Items: []LineItem{{Text: strings.TrimSpace(line)}}})
+		}
+	}
+	return
+}
+
+// formatDurationSRT formats an .srt duration
+func formatDurationSRT(i time.Duration) string {
+	return formatDuration(i, ",", 3)
+}
+
+// WriteToSRT writes subtitles in .srt format
+func (s Subtitles) WriteToSRT(o io.Writer) (err error) {
+	// Do not write anything if no subtitles
+	if len(s.Items) == 0 {
+		err = ErrNoSubtitlesToWrite
+		return
+	}
+
+	// Add BOM header
+	var c []byte
+	c = append(c, BytesBOM...)
+
+	// Loop through subtitles
+	for k, v := range s.Items {
+		// Add time boundaries
+		c = append(c, []byte(strconv.Itoa(k+1))...)
+		c = append(c, bytesLineSeparator...)
+		c = append(c, []byte(formatDurationSRT(v.StartAt))...)
+		c = append(c, bytesSRTTimeBoundariesSeparator...)
+		c = append(c, []byte(formatDurationSRT(v.EndAt))...)
+		c = append(c, bytesLineSeparator...)
+
+		// Loop through lines
+		for _, l := range v.Lines {
+			c = append(c, []byte(l.String())...)
+			c = append(c, bytesLineSeparator...)
+		}
+
+		// Add new line
+		c = append(c, bytesLineSeparator...)
+	}
+
+	// Remove last new line
+	c = c[:len(c)-1]
+
+	// Write
+	if _, err = o.Write(c); err != nil {
+		err = fmt.Errorf("astisub: writing failed: %w", err)
+		return
+	}
+	return
+}