rtmp: simplify Audio message structure (#2924)

internal/protocols/rtmp/message/audio.go

@@ -35,12 +35,6 @@ const (
 	Depth16 = 1
 )
 
-// audio channels
-const (
-	ChannelsMono   = 0
-	ChannelsStereo = 1
-)
-
 // AudioAACType is the AAC type of a Audio.
 type AudioAACType uint8
 
@@ -58,7 +52,7 @@ type Audio struct {
 	Codec           uint8
 	Rate            uint8
 	Depth           uint8
-	Channels        uint8
+	IsStereo        bool
 	AACType         AudioAACType // only for CodecMPEG4Audio
 	Payload         []byte
 }
@@ -82,7 +76,10 @@ func (m *Audio) Unmarshal(raw *rawmessage.Message) error {
 
 	m.Rate = (raw.Body[0] >> 2) & 0x03
 	m.Depth = (raw.Body[0] >> 1) & 0x01
-	m.Channels = raw.Body[0] & 0x01
+
+	if (raw.Body[0] & 0x01) != 0 {
+		m.IsStereo = true
+	}
 
 	if m.Codec == CodecMPEG4Audio {
 		m.AACType = AudioAACType(raw.Body[1])
@@ -114,7 +111,11 @@ func (m Audio) marshalBodySize() int {
 func (m Audio) Marshal() (*rawmessage.Message, error) {
 	body := make([]byte, m.marshalBodySize())
 
-	body[0] = m.Codec<<4 | m.Rate<<2 | m.Depth<<1 | m.Channels
+	body[0] = m.Codec<<4 | m.Rate<<2 | m.Depth<<1
+
+	if m.IsStereo {
+		body[0] |= 1
+	}
 
 	if m.Codec == CodecMPEG4Audio {
 		body[1] = uint8(m.AACType)

internal/protocols/rtmp/message/reader_test.go

@@ -35,7 +35,7 @@ var readWriterCases = []struct {
 			Codec:           CodecMPEG1Audio,
 			Rate:            Rate44100,
 			Depth:           Depth16,
-			Channels:        ChannelsStereo,
+			IsStereo:        true,
 			Payload:         []byte{0x01, 0x02, 0x03, 0x04},
 		},
 		[]byte{
@@ -52,7 +52,7 @@ var readWriterCases = []struct {
 			Codec:           CodecMPEG4Audio,
 			Rate:            Rate44100,
 			Depth:           Depth16,
-			Channels:        ChannelsStereo,
+			IsStereo:        true,
 			AACType:         AudioAACTypeAU,
 			Payload:         []byte{0x5A, 0xC0, 0x77, 0x40},
 		},

internal/protocols/rtmp/reader.go

@@ -333,7 +333,7 @@ func tracksFromMetadata(conn *Conn, payload []interface{}) (format.Format, forma
 						MULaw:      false,
 						SampleRate: 8000,
 						ChannelCount: func() int {
-							if msg.Channels == message.ChannelsStereo {
+							if msg.IsStereo {
 								return 2
 							}
 							return 1
@@ -346,7 +346,7 @@ func tracksFromMetadata(conn *Conn, payload []interface{}) (format.Format, forma
 						MULaw:      true,
 						SampleRate: 8000,
 						ChannelCount: func() int {
-							if msg.Channels == message.ChannelsStereo {
+							if msg.IsStereo {
 								return 2
 							}
 							return 1
@@ -364,10 +364,10 @@ func tracksFromMetadata(conn *Conn, payload []interface{}) (format.Format, forma
 						}(),
 						SampleRate: audioRateRTMPToInt(msg.Rate),
 						ChannelCount: func() int {
-							if msg.Channels == message.ChannelsMono {
-								return 1
+							if msg.IsStereo {
+								return 2
 							}
-							return 2
+							return 1
 						}(),
 					}
 				}

internal/protocols/rtmp/reader_test.go

@@ -174,7 +174,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecMPEG4Audio,
 					Rate:            message.Rate44100,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsStereo,
+					IsStereo:        true,
 					AACType:         message.AudioAACTypeConfig,
 					Payload: func() []byte {
 						enc, err := mpeg4audio.Config{
@@ -294,7 +294,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecMPEG4Audio,
 					Rate:            message.Rate44100,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsStereo,
+					IsStereo:        true,
 					AACType:         message.AudioAACTypeConfig,
 					Payload: func() []byte {
 						enc, err := mpeg4audio.Config{
@@ -329,7 +329,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecMPEG4Audio,
 					Rate:            message.Rate44100,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsStereo,
+					IsStereo:        true,
 					AACType:         message.AudioAACTypeConfig,
 					Payload: func() []byte {
 						enc, err := mpeg4audio.Config{
@@ -347,7 +347,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecMPEG4Audio,
 					Rate:            message.Rate44100,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsStereo,
+					IsStereo:        true,
 					AACType:         message.AudioAACTypeConfig,
 					Payload: func() []byte {
 						enc, err := mpeg4audio.Config{
@@ -430,7 +430,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecMPEG4Audio,
 					Rate:            message.Rate44100,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsStereo,
+					IsStereo:        true,
 					AACType:         message.AudioAACTypeConfig,
 					Payload: func() []byte {
 						enc, err := mpeg4audio.Config{
@@ -674,7 +674,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           0xa,
 					Rate:            0x3,
 					Depth:           0x1,
-					Channels:        0x1,
+					IsStereo:        true,
 					Payload:         []uint8{0x11, 0x88},
 				},
 			},
@@ -813,7 +813,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecPCMA,
 					Rate:            message.Rate5512,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsMono,
+					IsStereo:        false,
 					Payload:         []byte{1, 2, 3, 4},
 				},
 			},
@@ -848,7 +848,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecPCMU,
 					Rate:            message.Rate5512,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsMono,
+					IsStereo:        false,
 					Payload:         []byte{1, 2, 3, 4},
 				},
 			},
@@ -882,7 +882,7 @@ func TestReadTracks(t *testing.T) {
 					Codec:           message.CodecLPCM,
 					Rate:            message.Rate44100,
 					Depth:           message.Depth16,
-					Channels:        message.ChannelsStereo,
+					IsStereo:        true,
 					Payload:         []byte{1, 2, 3, 4},
 				},
 			},

internal/protocols/rtmp/writer.go

@@ -39,11 +39,8 @@ func audioRateIntToRTMP(v int) uint8 {
 	}
 }
 
-func mpeg1AudioChannels(m mpeg1audio.ChannelMode) uint8 {
-	if m == mpeg1audio.ChannelModeMono {
-		return message.ChannelsMono
-	}
-	return message.ChannelsStereo
+func mpeg1AudioChannels(m mpeg1audio.ChannelMode) bool {
+	return m != mpeg1audio.ChannelModeMono
 }
 
 // Writer is a wrapper around Conn that provides utilities to mux outgoing data.
@@ -156,7 +153,7 @@ func (w *Writer) writeTracks(videoTrack format.Format, audioTrack format.Format)
 			Codec:           message.CodecMPEG4Audio,
 			Rate:            message.Rate44100,
 			Depth:           message.Depth16,
-			Channels:        message.ChannelsStereo,
+			IsStereo:        true,
 			AACType:         message.AudioAACTypeConfig,
 			Payload:         enc,
 		})
@@ -195,7 +192,7 @@ func (w *Writer) WriteMPEG4Audio(pts time.Duration, au []byte) error {
 		Codec:           message.CodecMPEG4Audio,
 		Rate:            message.Rate44100,
 		Depth:           message.Depth16,
-		Channels:        message.ChannelsStereo,
+		IsStereo:        true,
 		AACType:         message.AudioAACTypeAU,
 		Payload:         au,
 		DTS:             pts,
@@ -210,7 +207,7 @@ func (w *Writer) WriteMPEG1Audio(pts time.Duration, h *mpeg1audio.FrameHeader, f
 		Codec:           message.CodecMPEG1Audio,
 		Rate:            audioRateIntToRTMP(h.SampleRate),
 		Depth:           message.Depth16,
-		Channels:        mpeg1AudioChannels(h.ChannelMode),
+		IsStereo:        mpeg1AudioChannels(h.ChannelMode),
 		Payload:         frame,
 		DTS:             pts,
 	})

internal/protocols/rtmp/writer_test.go

@@ -91,7 +91,7 @@ func TestWriteTracks(t *testing.T) {
 		Codec:           message.CodecMPEG4Audio,
 		Rate:            message.Rate44100,
 		Depth:           message.Depth16,
-		Channels:        message.ChannelsStereo,
+		IsStereo:        true,
 		AACType:         message.AudioAACTypeConfig,
 		Payload:         []byte{0x12, 0x10},
 	}, msg)