thought of how to address "alternatives" to fix inconsistency

reader.go

@@ -331,15 +331,11 @@ func decodeLineOfMasterPlaylist(p *MasterPlaylist, state *decodingState, line st
 				alt.URI = v
 			}
 		}
-		state.alternatives = append(state.alternatives, &alt)
+		p.Alternatives = append(p.Alternatives, &alt)
 	case !state.tagStreamInf && strings.HasPrefix(line, "#EXT-X-STREAM-INF:"):
 		state.tagStreamInf = true
 		state.listType = MASTER
 		state.variant = new(Variant)
-		if len(state.alternatives) > 0 {
-			state.variant.Alternatives = state.alternatives
-			state.alternatives = nil
-		}
 		p.Variants = append(p.Variants, state.variant)
 		for k, v := range decodeParamsLine(line[18:]) {
 			switch k {
@@ -395,10 +391,6 @@ func decodeLineOfMasterPlaylist(p *MasterPlaylist, state *decodingState, line st
 		state.listType = MASTER
 		state.variant = new(Variant)
 		state.variant.Iframe = true
-		if len(state.alternatives) > 0 {
-			state.variant.Alternatives = state.alternatives
-			state.alternatives = nil
-		}
 		p.Variants = append(p.Variants, state.variant)
 		for k, v := range decodeParamsLine(line[26:]) {
 			switch k {

reader_test.go

@@ -85,20 +85,26 @@ func TestDecodeMasterPlaylistWithAlternatives(t *testing.T) {
 		t.Fatal("not all variants in master playlist parsed")
 	}
 	// TODO check other values
-	for i, v := range p.Variants {
-		if i == 0 && len(v.Alternatives) != 3 {
-			t.Fatalf("not all alternatives from #EXT-X-MEDIA parsed (has %d but should be 3", len(v.Alternatives))
-		}
-		if i == 1 && len(v.Alternatives) != 3 {
-			t.Fatalf("not all alternatives from #EXT-X-MEDIA parsed (has %d but should be 3", len(v.Alternatives))
-		}
-		if i == 2 && len(v.Alternatives) != 3 {
-			t.Fatalf("not all alternatives from #EXT-X-MEDIA parsed (has %d but should be 3", len(v.Alternatives))
-		}
-		if i == 3 && len(v.Alternatives) > 0 {
-			t.Fatal("should not be alternatives for this variant")
+	var low_count, mid_count, hi_count int
+	for _, a := range p.Alternatives {
+		switch a.GroupId {
+		case "low":
+			low_count++
+		case "mid":
+			mid_count++
+		case "hi":
+			hi_count++
 		}
 	}
+	if low_count != 3 {
+		t.Fatalf("not all alternatives from #EXT-X-MEDIA parsed (has %d but should be 3", low_count)
+	}
+	if mid_count != 3 {
+		t.Fatalf("not all alternatives from #EXT-X-MEDIA parsed (has %d but should be 3", mid_count)
+	}
+	if hi_count != 3 {
+		t.Fatalf("not all alternatives from #EXT-X-MEDIA parsed (has %d but should be 3", hi_count)
+	}
 	// fmt.Println(p.Encode().String())
 }
 

structure.go

@@ -147,8 +147,9 @@ type MediaPlaylist struct {
 //    http://example.com/audio-only.m3u8
 type MasterPlaylist struct {
 	Variants            []*Variant
-	Args                string // optional arguments placed after URI (URI?Args)
-	CypherVersion       string // non-standard tag for Widevine (see also WV struct)
+	Alternatives        []*Alternative // EXT-X-MEDIA
+	Args                string         // optional arguments placed after URI (URI?Args)
+	CypherVersion       string         // non-standard tag for Widevine (see also WV struct)
 	buf                 bytes.Buffer
 	ver                 uint8
 	independentSegments bool
@@ -181,8 +182,7 @@ type VariantParams struct {
 	Iframe           bool   // EXT-X-I-FRAME-STREAM-INF
 	VideoRange       string
 	HDCPLevel        string
-	FrameRate        float64        // EXT-X-STREAM-INF
-	Alternatives     []*Alternative // EXT-X-MEDIA
+	FrameRate        float64 // EXT-X-STREAM-INF
 }
 
 // Alternative structure represents EXT-X-MEDIA tag in variants.
@@ -327,7 +327,6 @@ type decodingState struct {
 	duration           float64
 	title              string
 	variant            *Variant
-	alternatives       []*Alternative
 	xkey               *Key
 	xmap               *Map
 	scte               *SCTE

writer.go

@@ -14,7 +14,6 @@ package m3u8
 import (
 	"bytes"
 	"errors"
-	"fmt"
 	"math"
 	"strconv"
 	"strings"
@@ -43,6 +42,21 @@ func NewMasterPlaylist() *MasterPlaylist {
 	return p
 }
 
+func (p *MasterPlaylist) AppendAlternative(alt Alternative) {
+	a := new(Alternative)
+	*a = alt
+	p.Alternatives = append(p.Alternatives, a)
+	// From section 7:
+	// The EXT-X-MEDIA tag and the AUDIO, VIDEO and SUBTITLES attributes of
+	// the EXT-X-STREAM-INF tag are backward compatible to protocol version
+	// 1, but playback on older clients may not be desirable.  A server MAY
+	// consider indicating a EXT-X-VERSION of 4 or higher in the Master
+	// Playlist but is not required to do so.
+	version(&p.ver, 4) // so it is optional and in theory may be set to ver.1
+	// but more tests required
+	p.buf.Reset()
+}
+
 // Append appends a variant to master playlist. This operation does
 // reset playlist cache.
 func (p *MasterPlaylist) Append(uri string, chunklist *MediaPlaylist, params VariantParams) {
@@ -51,16 +65,6 @@ func (p *MasterPlaylist) Append(uri string, chunklist *MediaPlaylist, params Var
 	v.Chunklist = chunklist
 	v.VariantParams = params
 	p.Variants = append(p.Variants, v)
-	if len(v.Alternatives) > 0 {
-		// From section 7:
-		// The EXT-X-MEDIA tag and the AUDIO, VIDEO and SUBTITLES attributes of
-		// the EXT-X-STREAM-INF tag are backward compatible to protocol version
-		// 1, but playback on older clients may not be desirable.  A server MAY
-		// consider indicating a EXT-X-VERSION of 4 or higher in the Master
-		// Playlist but is not required to do so.
-		version(&p.ver, 4) // so it is optional and in theory may be set to ver.1
-		// but more tests required
-	}
 	p.buf.Reset()
 }
 
@@ -93,71 +97,63 @@ func (p *MasterPlaylist) Encode() *bytes.Buffer {
 		}
 	}
 
-	var altsWritten = make(map[string]bool)
-
-	for _, pl := range p.Variants {
-		if pl.Alternatives != nil {
-			for _, alt := range pl.Alternatives {
-				// Make sure that we only write out an alternative once
-				altKey := fmt.Sprintf("%s-%s-%s-%s", alt.Type, alt.GroupId, alt.Name, alt.Language)
-				if altsWritten[altKey] {
-					continue
-				}
-				altsWritten[altKey] = true
-
-				p.buf.WriteString("#EXT-X-MEDIA:")
-				if alt.Type != "" {
-					p.buf.WriteString("TYPE=") // Type should not be quoted
-					p.buf.WriteString(alt.Type)
-				}
-				if alt.GroupId != "" {
-					p.buf.WriteString(",GROUP-ID=\"")
-					p.buf.WriteString(alt.GroupId)
-					p.buf.WriteRune('"')
-				}
-				if alt.Name != "" {
-					p.buf.WriteString(",NAME=\"")
-					p.buf.WriteString(alt.Name)
-					p.buf.WriteRune('"')
-				}
-				p.buf.WriteString(",DEFAULT=")
-				if alt.Default {
-					p.buf.WriteString("YES")
-				} else {
-					p.buf.WriteString("NO")
-				}
-				if alt.Autoselect != "" {
-					p.buf.WriteString(",AUTOSELECT=")
-					p.buf.WriteString(alt.Autoselect)
-				}
-				if alt.Language != "" {
-					p.buf.WriteString(",LANGUAGE=\"")
-					p.buf.WriteString(alt.Language)
-					p.buf.WriteRune('"')
-				}
-				if alt.Forced != "" {
-					p.buf.WriteString(",FORCED=\"")
-					p.buf.WriteString(alt.Forced)
-					p.buf.WriteRune('"')
-				}
-				if alt.Characteristics != "" {
-					p.buf.WriteString(",CHARACTERISTICS=\"")
-					p.buf.WriteString(alt.Characteristics)
-					p.buf.WriteRune('"')
-				}
-				if alt.Subtitles != "" {
-					p.buf.WriteString(",SUBTITLES=\"")
-					p.buf.WriteString(alt.Subtitles)
-					p.buf.WriteRune('"')
-				}
-				if alt.URI != "" {
-					p.buf.WriteString(",URI=\"")
-					p.buf.WriteString(alt.URI)
-					p.buf.WriteRune('"')
-				}
-				p.buf.WriteRune('\n')
+	if p.Alternatives != nil {
+		for _, alt := range p.Alternatives {
+			p.buf.WriteString("#EXT-X-MEDIA:")
+			if alt.Type != "" {
+				p.buf.WriteString("TYPE=") // Type should not be quoted
+				p.buf.WriteString(alt.Type)
+			}
+			if alt.GroupId != "" {
+				p.buf.WriteString(",GROUP-ID=\"")
+				p.buf.WriteString(alt.GroupId)
+				p.buf.WriteRune('"')
+			}
+			if alt.Name != "" {
+				p.buf.WriteString(",NAME=\"")
+				p.buf.WriteString(alt.Name)
+				p.buf.WriteRune('"')
+			}
+			p.buf.WriteString(",DEFAULT=")
+			if alt.Default {
+				p.buf.WriteString("YES")
+			} else {
+				p.buf.WriteString("NO")
+			}
+			if alt.Autoselect != "" {
+				p.buf.WriteString(",AUTOSELECT=")
+				p.buf.WriteString(alt.Autoselect)
+			}
+			if alt.Language != "" {
+				p.buf.WriteString(",LANGUAGE=\"")
+				p.buf.WriteString(alt.Language)
+				p.buf.WriteRune('"')
+			}
+			if alt.Forced != "" {
+				p.buf.WriteString(",FORCED=\"")
+				p.buf.WriteString(alt.Forced)
+				p.buf.WriteRune('"')
 			}
+			if alt.Characteristics != "" {
+				p.buf.WriteString(",CHARACTERISTICS=\"")
+				p.buf.WriteString(alt.Characteristics)
+				p.buf.WriteRune('"')
+			}
+			if alt.Subtitles != "" {
+				p.buf.WriteString(",SUBTITLES=\"")
+				p.buf.WriteString(alt.Subtitles)
+				p.buf.WriteRune('"')
+			}
+			if alt.URI != "" {
+				p.buf.WriteString(",URI=\"")
+				p.buf.WriteString(alt.URI)
+				p.buf.WriteRune('"')
+			}
+			p.buf.WriteRune('\n')
 		}
+	}
+
+	for _, pl := range p.Variants {
 		if pl.Iframe {
 			p.buf.WriteString("#EXT-X-I-FRAME-STREAM-INF:PROGRAM-ID=")
 			p.buf.WriteString(strconv.FormatUint(uint64(pl.ProgramId), 10))

writer_test.go

@@ -789,7 +789,8 @@ func TestNewMasterPlaylistWithAlternatives(t *testing.T) {
 			t.Errorf("Add segment #%d to a media playlist failed: %s", i, e)
 		}
 	}
-	m.Append("chunklist1.m3u8", p, VariantParams{Alternatives: []*Alternative{audioAlt}})
+	m.Append("chunklist1.m3u8", p, VariantParams{})
+	m.AppendAlternative(*audioAlt)
 
 	if m.ver != 4 {
 		t.Fatalf("Expected version 4, actual, %d", m.ver)