Add CHANNELS attribute for alternative renditions

reader.go

@@ -325,6 +325,8 @@ func decodeLineOfMasterPlaylist(p *MasterPlaylist, state *decodingState, line st
 				alt.Forced = v
 			case "CHARACTERISTICS":
 				alt.Characteristics = v
+			case "CHANNELS":
+				alt.Channels = v
 			case "SUBTITLES":
 				alt.Subtitles = v
 			case "URI":

structure.go

@@ -193,6 +193,7 @@ type Alternative struct {
 	Autoselect      string
 	Forced          string
 	Characteristics string
+	Channels        string
 	Subtitles       string
 }
 

writer.go

@@ -145,6 +145,11 @@ func (p *MasterPlaylist) Encode() *bytes.Buffer {
 					p.buf.WriteString(alt.Characteristics)
 					p.buf.WriteRune('"')
 				}
+				if alt.Channels != "" {
+					p.buf.WriteString(",CHANNELS=\"")
+					p.buf.WriteString(alt.Channels)
+					p.buf.WriteRune('"')
+				}
 				if alt.Subtitles != "" {
 					p.buf.WriteString(",SUBTITLES=\"")
 					p.buf.WriteString(alt.Subtitles)

writer_test.go

@@ -777,6 +777,7 @@ func TestNewMasterPlaylistWithAlternatives(t *testing.T) {
 		Name:       "main",
 		Default:    true,
 		Autoselect: "YES",
+		Channels:   "2",
 		Language:   "english",
 	}
 	p, e := NewMediaPlaylist(3, 5)
@@ -794,7 +795,7 @@ func TestNewMasterPlaylistWithAlternatives(t *testing.T) {
 	if m.ver != 4 {
 		t.Fatalf("Expected version 4, actual, %d", m.ver)
 	}
-	expected := `#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio",NAME="main",DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="english",URI="800/rendition.m3u8"`
+	expected := `#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio",NAME="main",DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="english",CHANNELS="2",URI="800/rendition.m3u8"`
 	if !strings.Contains(m.String(), expected) {
 		t.Fatalf("Master playlist did not contain: %s\nMaster Playlist:\n%v", expected, m.String())
 	}