Add INSTREAM-ID attribute for CLOSED-CAPTIONS

reader.go

@@ -323,6 +323,8 @@ func decodeLineOfMasterPlaylist(p *MasterPlaylist, state *decodingState, line st
 				alt.Autoselect = v
 			case "FORCED":
 				alt.Forced = v
+			case "INSTREAM-ID":
+				alt.InstreamID = v
 			case "CHARACTERISTICS":
 				alt.Characteristics = v
 			case "SUBTITLES":

structure.go

@@ -192,6 +192,7 @@ type Alternative struct {
 	Default         bool
 	Autoselect      string
 	Forced          string
+	InstreamID      string
 	Characteristics string
 	Subtitles       string
 }

writer.go

@@ -140,6 +140,11 @@ func (p *MasterPlaylist) Encode() *bytes.Buffer {
 					p.buf.WriteString(alt.Forced)
 					p.buf.WriteRune('"')
 				}
+				if alt.Type == "CLOSED-CAPTIONS" && alt.InstreamID != "" {
+					p.buf.WriteString(",INSTREAM-ID=\"")
+					p.buf.WriteString(alt.InstreamID)
+					p.buf.WriteRune('"')
+				}
 				if alt.Characteristics != "" {
 					p.buf.WriteString(",CHARACTERISTICS=\"")
 					p.buf.WriteString(alt.Characteristics)