Improve WebVTT to TTML conversion

subtitles.go

@@ -428,6 +428,94 @@ func (sa *StyleAttributes) propagateWebVTTAttributes() {
 	sa.SRTBold = sa.WebVTTBold
 	sa.SRTItalics = sa.WebVTTItalics
 	sa.SRTUnderline = sa.WebVTTUnderline
+
+	// may be overridden by position parsing later
+	switch sa.WebVTTAlign {
+	case "left", "right", "center", "start", "end":
+		sa.TTMLTextAlign = astikit.StrPtr(sa.WebVTTAlign)
+	}
+
+	for _, tag := range sa.WebVTTTags {
+		switch tag.Name {
+		case "c":
+			if len(tag.Classes) > 0 {
+				for _, color := range tag.Classes {
+					if strings.HasPrefix(color, "bg_") && len(color) > 3 {
+						if bgColor, err := parseWebVTTColorClass(color[3:]); err == nil {
+							sa.TTMLBackgroundColor = astikit.StrPtr("#" + bgColor.TTMLString())
+						}
+					} else {
+						if fgColor, err := parseWebVTTColorClass(color); err == nil {
+							sa.TTMLColor = astikit.StrPtr("#" + fgColor.TTMLString())
+						}
+					}
+				}
+			}
+		}
+	}
+
+	// Handle WebVTT position and alignment conversion
+	sa.handleWebVTTPositioning()
+
+	if sa.WebVTTSize != "" {
+		sa.TTMLExtent = astikit.StrPtr(fmt.Sprintf("%s 10%%", sa.WebVTTSize))
+	}
+}
+
+// parseWebVTTPosition parses WebVTT position string like "10%,line-left".
+// Returns (xPosition, alignment)
+func (sa *StyleAttributes) parseWebVTTPosition() (string, string) {
+	if sa.WebVTTPosition == "" {
+		return "", ""
+	}
+
+	parts := strings.Split(sa.WebVTTPosition, ",")
+	if len(parts) != 2 {
+		return sa.WebVTTPosition, ""
+	}
+
+	return strings.TrimSpace(parts[0]), strings.TrimSpace(parts[1])
+}
+
+// handleWebVTTPositioning handles WebVTT position and line attributes conversion
+func (sa *StyleAttributes) handleWebVTTPositioning() {
+	var xPos, yPos string
+	var hasPosition, hasLine bool
+
+	// Parse position if available
+	if sa.WebVTTPosition != "" {
+		hasPosition = true
+		var alignment string
+		xPos, alignment = sa.parseWebVTTPosition()
+
+		// Handle position alignment (takes precedence over WebVTTAlign)
+		switch alignment {
+		case "line-left":
+			sa.TTMLTextAlign = astikit.StrPtr("left")
+		case "center":
+			sa.TTMLTextAlign = astikit.StrPtr("center")
+		case "line-right":
+			sa.TTMLTextAlign = astikit.StrPtr("right")
+		}
+	}
+
+	// Handle line if available
+	if sa.WebVTTLine != "" {
+		hasLine = true
+		yPos = sa.WebVTTLine
+	}
+
+	// Set TTMLOrigin based on available position and line data
+	if hasPosition && hasLine {
+		// Both position and line are available
+		sa.TTMLOrigin = astikit.StrPtr(fmt.Sprintf("%s %s", xPos, yPos))
+	} else if hasPosition {
+		// Only position is available, use default Y position (80% for bottom)
+		sa.TTMLOrigin = astikit.StrPtr(fmt.Sprintf("%s 80%%", xPos))
+	} else if hasLine {
+		// Only line is available, use default X position (10% for left)
+		sa.TTMLOrigin = astikit.StrPtr(fmt.Sprintf("10%% %s", yPos))
+	}
 }
 
 // merge - base on parent, override style attributes if defined in child

testdata/example-in.vtt

@@ -33,7 +33,7 @@ NOTE This a comment inside the VTT
 and this is the second line
 
 2
-00:02:04.08 --> 00:02:07.12  region:fred position:10%,start align:left size:35%
+00:02:04.08 --> 00:02:07.12  region:fred position:10%,line-left align:left size:35%
 MAN:
 How did we end up here?
 

testdata/example-out.vtt

@@ -29,7 +29,7 @@ NOTE This a comment inside the VTT
 and this is the second line
 
 2
-00:02:04.080 --> 00:02:07.120 align:left position:10%,start region:fred size:35%
+00:02:04.080 --> 00:02:07.120 align:left position:10%,line-left region:fred size:35%
 MAN:
 How did we end up here?
 

webvtt.go

@@ -648,10 +648,21 @@ func (li LineItem) webVTTBytes(previous, next *LineItem) (c []byte) {
 		c = append(c, []byte("<"+formatDurationWebVTT(li.StartAt)+">")...)
 	}
 
-	// Get color
+	// Get color - only add TTMLColor-based tag if there are no WebVTT color tags
 	var color string
-	if li.InlineStyle != nil && li.InlineStyle.TTMLColor != nil {
-		color = cssColor(*li.InlineStyle.TTMLColor)
+	var hasColorTags bool
+	if li.InlineStyle != nil {
+		// Check if we have WebVTT color tags
+		for _, tag := range li.InlineStyle.WebVTTTags {
+			if tag.Name == "c" {
+				hasColorTags = true
+				break
+			}
+		}
+		// Only use TTMLColor if we don't have WebVTT color tags
+		if !hasColorTags && li.InlineStyle.TTMLColor != nil {
+			color = cssColor(*li.InlineStyle.TTMLColor)
+		}
 	}
 
 	// Append
@@ -692,3 +703,30 @@ func cssColor(rgb string) string {
 	}
 	return colors[strings.ToLower(rgb)] // returning the empty string is ok
 }
+
+// webVTTColorMap maps WebVTT color class names to Color instances
+var webVTTColorMap = map[string]*Color{
+	"black":   ColorBlack,
+	"red":     ColorRed,
+	"green":   ColorGreen,
+	"yellow":  ColorYellow,
+	"blue":    ColorBlue,
+	"magenta": ColorMagenta,
+	"cyan":    ColorCyan,
+	"white":   ColorWhite,
+	"silver":  ColorSilver,
+	"gray":    ColorGray,
+	"maroon":  ColorMaroon,
+	"olive":   ColorOlive,
+	"lime":    ColorLime,
+	"teal":    ColorTeal,
+	"navy":    ColorNavy,
+	"purple":  ColorPurple,
+}
+
+func parseWebVTTColorClass(color string) (*Color, error) {
+	if c, ok := webVTTColorMap[color]; ok {
+		return c, nil
+	}
+	return nil, fmt.Errorf("unknown color class %s", color)
+}

webvtt_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/asticode/go-astikit"
 	"github.com/asticode/go-astisub"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -27,7 +28,16 @@ func TestWebVTT(t *testing.T) {
 	assert.Equal(t, s.Regions["bill"], s.Items[0].Region)
 	assert.Equal(t, s.Regions["fred"], s.Items[1].Region)
 	// Styles
-	assert.Equal(t, astisub.StyleAttributes{WebVTTAlign: "left", WebVTTPosition: "10%,start", WebVTTSize: "35%"}, *s.Items[1].InlineStyle)
+	expected := astisub.StyleAttributes{
+		WebVTTAlign:    "left",
+		WebVTTPosition: "10%,line-left",
+		WebVTTSize:     "35%",
+	}
+	// propagateWebVTTAttributes() sets these based on WebVTT attributes
+	expected.TTMLTextAlign = astikit.StrPtr("left") // From WebVTTAlign since "start" is not a valid position alignment
+	expected.TTMLOrigin = astikit.StrPtr("10% 80%") // From position: 10% X, 80% Y (default when no line specified)
+	expected.TTMLExtent = astikit.StrPtr("35% 10%") // From size: 35% width, 10% height (default when no line specified)
+	assert.Equal(t, expected, *s.Items[1].InlineStyle)
 
 	// No subtitles to write
 	w := &bytes.Buffer{}
@@ -255,3 +265,85 @@ func TestWebVTTParseDuration(t *testing.T) {
 	assert.NotNil(t, s.Items[1].InlineStyle)
 	assert.Equal(t, s.Items[1].InlineStyle.WebVTTAlign, "middle")
 }
+
+func TestWebVTTColorToTTML(t *testing.T) {
+	testData := `WEBVTT
+
+1
+00:00:01.000 --> 00:00:03.000
+<c.red>Red text</c> and <c.blue.bg_yellow>blue text on yellow background</c>
+
+2
+00:00:04.000 --> 00:00:06.000
+<c.green>Green text</c> with <c.bg_cyan>text on cyan background</c>
+
+3
+00:00:07.000 --> 00:00:09.000
+Normal text with <c.magenta>magenta</c> and <c.orange>unknown color</c>`
+
+	s, err := astisub.ReadFromWebVTT(strings.NewReader(testData))
+	require.NoError(t, err)
+	require.Len(t, s.Items, 3)
+
+	// Test item 1: Red text and blue text on yellow background
+	item1 := s.Items[0]
+	require.Len(t, item1.Lines, 1)
+	require.Len(t, item1.Lines[0].Items, 3) // "Red text", " and ", "blue text on yellow background"
+
+	// Check red text
+	redItem := item1.Lines[0].Items[0]
+	assert.Equal(t, "Red text", redItem.Text)
+	require.NotNil(t, redItem.InlineStyle)
+	require.NotNil(t, redItem.InlineStyle.TTMLColor)
+	assert.Equal(t, "#ff0000", *redItem.InlineStyle.TTMLColor) // Red color
+	assert.Nil(t, redItem.InlineStyle.TTMLBackgroundColor)
+
+	// Check blue text on yellow background
+	blueYellowItem := item1.Lines[0].Items[2]
+	assert.Equal(t, "blue text on yellow background", blueYellowItem.Text)
+	require.NotNil(t, blueYellowItem.InlineStyle)
+	require.NotNil(t, blueYellowItem.InlineStyle.TTMLColor)
+	require.NotNil(t, blueYellowItem.InlineStyle.TTMLBackgroundColor)
+	assert.Equal(t, "#0000ff", *blueYellowItem.InlineStyle.TTMLColor)           // Blue color
+	assert.Equal(t, "#ffff00", *blueYellowItem.InlineStyle.TTMLBackgroundColor) // Yellow background
+
+	// Test item 2: Green text and background color only
+	item2 := s.Items[1]
+	require.Len(t, item2.Lines, 1)
+	require.Len(t, item2.Lines[0].Items, 3) // "Green text", " with ", "text on cyan background"
+
+	// Check green text
+	greenItem := item2.Lines[0].Items[0]
+	assert.Equal(t, "Green text", greenItem.Text)
+	require.NotNil(t, greenItem.InlineStyle)
+	require.NotNil(t, greenItem.InlineStyle.TTMLColor)
+	assert.Equal(t, "#008000", *greenItem.InlineStyle.TTMLColor) // Green color
+	assert.Nil(t, greenItem.InlineStyle.TTMLBackgroundColor)
+
+	// Check text with cyan background only
+	cyanBgItem := item2.Lines[0].Items[2]
+	assert.Equal(t, "text on cyan background", cyanBgItem.Text)
+	require.NotNil(t, cyanBgItem.InlineStyle)
+	assert.Nil(t, cyanBgItem.InlineStyle.TTMLColor) // No foreground color specified
+	require.NotNil(t, cyanBgItem.InlineStyle.TTMLBackgroundColor)
+	assert.Equal(t, "#00ffff", *cyanBgItem.InlineStyle.TTMLBackgroundColor) // Cyan background
+
+	// Test item 3: Known and unknown colors
+	item3 := s.Items[2]
+	require.Len(t, item3.Lines, 1)
+	require.Len(t, item3.Lines[0].Items, 4) // "Normal text with ", "magenta", " and ", "unknown color"
+
+	// Check magenta text (known color)
+	magentaItem := item3.Lines[0].Items[1]
+	assert.Equal(t, "magenta", magentaItem.Text)
+	require.NotNil(t, magentaItem.InlineStyle)
+	require.NotNil(t, magentaItem.InlineStyle.TTMLColor)
+	assert.Equal(t, "#ff00ff", *magentaItem.InlineStyle.TTMLColor) // Magenta color
+
+	// Check unknown color (should not set TTMLColor because "orange" is not in webVTTColorMap)
+	unknownColorItem := item3.Lines[0].Items[3]
+	assert.Equal(t, "unknown color", unknownColorItem.Text)
+	require.NotNil(t, unknownColorItem.InlineStyle)
+	assert.Nil(t, unknownColorItem.InlineStyle.TTMLColor) // Unknown color should not be converted
+	assert.Nil(t, unknownColorItem.InlineStyle.TTMLBackgroundColor)
+}