fix: EXT-X-MAP is written and stored when changed

CHANGELOG.md

@@ -16,6 +16,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - EXT-X-START was not written for negative values
+- EXT-X-MAP is written when changed
+
+### Chore
+
+- Refactored EXT-X-DEFINE and EXT-X-MAP parsing and writing
 
 ## [v0.3.0] 2025-01-14
 

m3u8/reader.go

@@ -677,6 +677,21 @@ func parseSessionData(line string) (*SessionData, error) {
 	return &sd, nil
 }
 
+func parseExtXMapParameters(parameters string) (*Map, error) {
+	m := Map{}
+	for _, attr := range decodeAttributes(parameters) {
+		switch attr.Key {
+		case "URI":
+			m.URI = attr.Val
+		case "BYTERANGE":
+			if _, err := fmt.Sscanf(attr.Val, "%d@%d", &m.Limit, &m.Offset); err != nil {
+				return nil, fmt.Errorf("byterange sub-range length value parsing error: %w", err)
+			}
+		}
+	}
+	return &m, nil
+}
+
 func parseKeyParams(parameters string) *Key {
 	key := Key{}
 	for _, attr := range decodeAttributes(parameters) {
@@ -768,7 +783,16 @@ func decodeLineOfMediaPlaylist(p *MediaPlaylist, state *decodingState, line stri
 		}
 	case !strings.HasPrefix(line, "#"):
 		if state.tagInf {
-			err := p.Append(line, state.duration, state.title)
+			seg := MediaSegment{
+				URI:      line,
+				Duration: state.duration,
+				Title:    state.title,
+			}
+			if state.lastReadMap != nil && !state.lastReadMap.Equal(state.lastStoredMap) {
+				seg.Map = state.lastReadMap
+				state.lastStoredMap = state.lastReadMap
+			}
+			err := p.AppendSegment(&seg)
 			if err == ErrPlaylistFull {
 				// Extend playlist by doubling size, reset internal state, try again.
 				// If the second Append fails, the if err block will handle it.
@@ -777,7 +801,7 @@ func decodeLineOfMediaPlaylist(p *MediaPlaylist, state *decodingState, line stri
 				p.Segments = append(p.Segments, make([]*MediaSegment, p.Count())...)
 				p.capacity = uint(len(p.Segments))
 				p.tail = p.count
-				err = p.Append(line, state.duration, state.title)
+				err = p.AppendSegment(&seg)
 			}
 			// Check err for first or subsequent Append()
 			if err != nil {
@@ -829,17 +853,6 @@ func decodeLineOfMediaPlaylist(p *MediaPlaylist, state *decodingState, line stri
 			}
 			state.tagKey = false
 		}
-		// If EXT-X-MAP appeared before reference to segment (EXTINF) then it linked to this segment
-		if state.tagMap {
-			p.Segments[p.last()].Map = &Map{state.xmap.URI, state.xmap.Limit, state.xmap.Offset}
-			// First EXT-X-MAP may appeared in the header of the playlist and linked to first segment
-			// but for convenient playlist generation it also linked as default playlist map
-			if p.Map == nil {
-				p.Map = state.xmap
-			}
-			state.tagMap = false
-		}
-
 		// if segment custom tag appeared before EXTINF then it links to this segment
 		if state.tagCustom {
 			p.Segments[p.last()].Custom = state.custom
@@ -904,18 +917,17 @@ func decodeLineOfMediaPlaylist(p *MediaPlaylist, state *decodingState, line stri
 		state.tagKey = true
 	case strings.HasPrefix(line, "#EXT-X-MAP:"):
 		state.listType = MEDIA
-		state.xmap = new(Map)
-		for k, v := range decodeAndTrimAttributes(line[11:]) {
-			switch k {
-			case "URI":
-				state.xmap.URI = v
-			case "BYTERANGE":
-				if _, err = fmt.Sscanf(v, "%d@%d", &state.xmap.Limit, &state.xmap.Offset); strict && err != nil {
-					return fmt.Errorf("byterange sub-range length value parsing error: %w", err)
-				}
-			}
+		xMap, err := parseExtXMapParameters(line[11:])
+		if err != nil {
+			return fmt.Errorf("error parsing EXT-X-MAP: %w", err)
+		}
+		if state.lastReadMap == nil && p.Count() == 0 {
+			p.Map = xMap
+			state.lastStoredMap = xMap
+		}
+		if state.lastReadMap == nil || !state.lastReadMap.Equal(xMap) {
+			state.lastReadMap = xMap
 		}
-		state.tagMap = true
 	case !state.tagProgramDateTime && strings.HasPrefix(line, "#EXT-X-PROGRAM-DATE-TIME:"):
 		state.tagProgramDateTime = true
 		state.listType = MEDIA

m3u8/structure.go

@@ -268,6 +268,17 @@ type Map struct {
 	Offset int64  // [@o] is offset from the start of the file under URI
 }
 
+// Equal compares two MediaSegment for equality.
+func (m *Map) Equal(other *Map) bool {
+	if m == nil && other == nil {
+		return true
+	}
+	if m == nil || other == nil {
+		return false
+	}
+	return m.URI == other.URI && m.Limit == other.Limit && m.Offset == other.Offset
+}
+
 // Internal structure for decoding a line of input stream with a list type detection
 type decodingState struct {
 	listType           ListType
@@ -279,7 +290,6 @@ type decodingState struct {
 	tagDiscontinuity   bool
 	tagProgramDateTime bool
 	tagKey             bool
-	tagMap             bool
 	tagCustom          bool
 	programDateTime    time.Time
 	limit              int64
@@ -289,7 +299,8 @@ type decodingState struct {
 	variant            *Variant
 	alternatives       []*Alternative
 	xkey               *Key
-	xmap               *Map
+	lastReadMap        *Map
+	lastStoredMap      *Map
 	scte               *SCTE
 	scte35DateRanges   []*DateRange
 	custom             CustomMap

m3u8/writer.go

@@ -389,6 +389,20 @@ func writeExtXStart(buf *bytes.Buffer, startTime float64, precise bool) {
 	buf.WriteRune('\n')
 }
 
+func writeExtXMap(buf *bytes.Buffer, m *Map) {
+	buf.WriteString("#EXT-X-MAP:")
+	buf.WriteString("URI=\"")
+	buf.WriteString(m.URI)
+	buf.WriteRune('"')
+	if m.Limit > 0 {
+		buf.WriteString(",BYTERANGE=")
+		buf.WriteString(strconv.FormatInt(m.Limit, 10))
+		buf.WriteRune('@')
+		buf.WriteString(strconv.FormatInt(m.Offset, 10))
+	}
+	buf.WriteRune('\n')
+}
+
 func writeKey(tag string, buf *bytes.Buffer, key *Key) {
 	buf.WriteString(tag)
 	buf.WriteString("METHOD=")
@@ -631,6 +645,8 @@ func (p *MediaPlaylist) Encode() *bytes.Buffer {
 		return &p.buf
 	}
 
+	var lastMap *Map
+
 	p.buf.WriteString("#EXTM3U\n#EXT-X-VERSION:")
 	p.buf.WriteString(strVer(p.ver))
 	p.buf.WriteRune('\n')
@@ -664,20 +680,6 @@ func (p *MediaPlaylist) Encode() *bytes.Buffer {
 		writeKey("#EXT-X-KEY:", &p.buf, p.Key)
 	}
 
-	// default MAP before any segment
-	if p.Map != nil {
-		p.buf.WriteString("#EXT-X-MAP:")
-		p.buf.WriteString("URI=\"")
-		p.buf.WriteString(p.Map.URI)
-		p.buf.WriteRune('"')
-		if p.Map.Limit > 0 {
-			p.buf.WriteString(",BYTERANGE=")
-			p.buf.WriteString(strconv.FormatInt(p.Map.Limit, 10))
-			p.buf.WriteRune('@')
-			p.buf.WriteString(strconv.FormatInt(p.Map.Offset, 10))
-		}
-		p.buf.WriteRune('\n')
-	}
 	if p.MediaType > 0 {
 		p.buf.WriteString("#EXT-X-PLAYLIST-TYPE:")
 		switch p.MediaType {
@@ -704,6 +706,10 @@ func (p *MediaPlaylist) Encode() *bytes.Buffer {
 	if p.Iframe {
 		p.buf.WriteString("#EXT-X-I-FRAMES-ONLY\n")
 	}
+	if p.Map != nil {
+		writeExtXMap(&p.buf, p.Map)
+		lastMap = p.Map
+	}
 
 	var (
 		seg           *MediaSegment
@@ -774,19 +780,10 @@ func (p *MediaPlaylist) Encode() *bytes.Buffer {
 		if seg.Discontinuity {
 			p.buf.WriteString("#EXT-X-DISCONTINUITY\n")
 		}
-		// ignore segment Map if default playlist Map is present
-		if p.Map == nil && seg.Map != nil {
-			p.buf.WriteString("#EXT-X-MAP:")
-			p.buf.WriteString("URI=\"")
-			p.buf.WriteString(seg.Map.URI)
-			p.buf.WriteRune('"')
-			if seg.Map.Limit > 0 {
-				p.buf.WriteString(",BYTERANGE=")
-				p.buf.WriteString(strconv.FormatInt(seg.Map.Limit, 10))
-				p.buf.WriteRune('@')
-				p.buf.WriteString(strconv.FormatInt(seg.Map.Offset, 10))
-			}
-			p.buf.WriteRune('\n')
+		// ignore segment Map if already written
+		if seg.Map != nil && !seg.Map.Equal(lastMap) {
+			writeExtXMap(&p.buf, seg.Map)
+			lastMap = seg.Map
 		}
 		if !seg.ProgramDateTime.IsZero() {
 			p.buf.WriteString("#EXT-X-PROGRAM-DATE-TIME:")

m3u8/writer_test.go

@@ -261,25 +261,44 @@ test01.ts`
 
 // Create new media playlist
 // Set default map
-// Add segment to media playlist
-// Set map on segment (should be ignored when encoding)
+// Add segment to media playlist with two different maps.
+// Only the second should be included in the playlist.
 func TestEncodeMediaPlaylistWithDefaultMap(t *testing.T) {
 	is := is.New(t)
-	p, e := NewMediaPlaylist(3, 5)
-	is.NoErr(e) // Create media playlist should be successful
+	p, err := NewMediaPlaylist(3, 5)
+	is.NoErr(err) // Create media playlist should be successful
 	p.SetDefaultMap("https://example.com", 1000*1024, 1024*1024)
 
-	e = p.Append("test01.ts", 5.0, "")
-	is.NoErr(e) // Add 1st segment to a media playlist should be successful
-	e = p.SetMap("https://notencoded.com", 1000*1024, 1024*1024)
-	is.NoErr(e) // Set map to a media playlist should be successful, but not set
+	err = p.Append("test01.ts", 5.0, "")
+	is.NoErr(err) // Add 1st segment to a media playlist should be successful
+	err = p.SetMap("https://example.com", 1000*1024, 1024*1024)
+	is.NoErr(err) // Set map to a media playlist should be successful, but not set since same as default.
+
+	err = p.Append("test02.ts", 5.0, "")
+	is.NoErr(err) // Add 1st segment to a media playlist should be successful
+	err = p.SetMap("https://example2.com", 1000*1024, 1024*1024)
+	is.NoErr(err) // Set map to a media playlist should be successful, but not set since same as already set.
+
+	err = p.SetDiscontinuity()
+	is.NoErr(err) // Set discontinuity tag should be successful
+
+	err = p.Append("test03.ts", 5.0, "")
+	is.NoErr(err) // Add 1st segment to a media playlist should be successful
+	err = p.SetMap("https://example2.com", 1000*1024, 1024*1024)
+	is.NoErr(err) // Set map to a media playlist should be successful, but not set since same as already set.
 
 	encoded := p.String()
 	expected := `EXT-X-MAP:URI="https://example.com",BYTERANGE=1024000@1048576`
-	is.True(strings.Contains(encoded, expected)) // default map is included in the playlist
+	is.Equal(1, strings.Count(encoded, expected)) // default map is included in the playlist just once
+
+	expected = `EXT-X-MAP:URI="https://example2.com",BYTERANGE=1024000@1048576`
+	is.Equal(1, strings.Count(encoded, expected)) // new map is included in the playlist just once
+
+	split := strings.Split(encoded, "#EXT-X-DISCONTINUITY")
+	is.Equal(2, len(split)) // discontinuity tag is included one time
 
-	ignored := `EXT-X-MAP:URI="https://notencoded.com"`
-	is.True(!strings.Contains(encoded, ignored)) // additional map is not included in the playlist
+	expected = `EXT-X-MAP:URI="https://example2.com",BYTERANGE=1024000@1048576`
+	is.Equal(1, strings.Count(split[1], expected)) // new map should be after discontinuity tag
 }
 
 // Create new media playlist