rtmp: fix reading metadata from onMetadata

when there's no audio and Conn is a client, onMetadata was skipped and
tracks were read by using the fallback method. Fix this.

internal/rtmp/conn.go

@@ -802,7 +802,28 @@ outer:
 
 // ReadTracks reads track informations.
 func (c *Conn) ReadTracks() (*gortsplib.TrackH264, *gortsplib.TrackMPEG4Audio, error) {
-	msg, err := c.ReadMessage()
+	msg, err := func() (message.Message, error) {
+		for {
+			msg, err := c.ReadMessage()
+			if err != nil {
+				return nil, err
+			}
+
+			// skip play start and data start
+			if cmd, ok := msg.(*message.MsgCommandAMF0); ok && cmd.Name == "onStatus" {
+				continue
+			}
+
+			// skip RtmpSampleAccess
+			if data, ok := msg.(*message.MsgDataAMF0); ok && len(data.Payload) >= 1 {
+				if s, ok := data.Payload[0].(string); ok && s == "|RtmpSampleAccess" {
+					continue
+				}
+			}
+
+			return msg, nil
+		}
+	}()
 	if err != nil {
 		return nil, nil, err
 	}
@@ -810,11 +831,6 @@ func (c *Conn) ReadTracks() (*gortsplib.TrackH264, *gortsplib.TrackMPEG4Audio, e
 	if data, ok := msg.(*message.MsgDataAMF0); ok && len(data.Payload) >= 1 {
 		payload := data.Payload
 
-		// skip packet
-		if s, ok := payload[0].(string); ok && s == "|RtmpSampleAccess" {
-			return c.ReadTracks()
-		}
-
 		if s, ok := payload[0].(string); ok && s == "@setDataFrame" {
 			payload = payload[1:]
 		}

internal/rtmp/conn_test.go

@@ -495,7 +495,8 @@ func TestReadTracks(t *testing.T) {
 	}
 
 	for _, ca := range []string{
-		"standard",
+		"video+audio",
+		"video",
 		"metadata without codec id",
 		"missing metadata",
 	} {
@@ -519,7 +520,7 @@ func TestReadTracks(t *testing.T) {
 				require.NoError(t, err)
 
 				switch ca {
-				case "standard":
+				case "video+audio":
 					require.Equal(t, &gortsplib.TrackH264{
 						PayloadType: 96,
 						SPS:         sps,
@@ -538,6 +539,15 @@ func TestReadTracks(t *testing.T) {
 						IndexDeltaLength: 3,
 					}, audioTrack)
 
+				case "video":
+					require.Equal(t, &gortsplib.TrackH264{
+						PayloadType: 96,
+						SPS:         sps,
+						PPS:         pps,
+					}, videoTrack)
+
+					require.Nil(t, audioTrack)
+
 				case "metadata without codec id":
 					require.Equal(t, &gortsplib.TrackH264{
 						PayloadType: 96,
@@ -740,7 +750,7 @@ func TestReadTracks(t *testing.T) {
 			}, msg)
 
 			switch ca {
-			case "standard":
+			case "video+audio":
 				// C->S metadata
 				err = mrw.Write(&message.MsgDataAMF0{
 					ChunkStreamID:   4,
@@ -802,6 +812,50 @@ func TestReadTracks(t *testing.T) {
 				})
 				require.NoError(t, err)
 
+			case "video":
+				// C->S metadata
+				err = mrw.Write(&message.MsgDataAMF0{
+					ChunkStreamID:   4,
+					MessageStreamID: 1,
+					Payload: []interface{}{
+						"@setDataFrame",
+						"onMetaData",
+						flvio.AMFMap{
+							{
+								K: "videodatarate",
+								V: float64(0),
+							},
+							{
+								K: "videocodecid",
+								V: float64(codecH264),
+							},
+							{
+								K: "audiodatarate",
+								V: float64(0),
+							},
+							{
+								K: "audiocodecid",
+								V: float64(0),
+							},
+						},
+					},
+				})
+				require.NoError(t, err)
+
+				// C->S H264 decoder config
+				buf, _ := h264conf.Conf{
+					SPS: sps,
+					PPS: pps,
+				}.Marshal()
+				err = mrw.Write(&message.MsgVideo{
+					ChunkStreamID:   6,
+					MessageStreamID: 1,
+					IsKeyFrame:      true,
+					H264Type:        flvio.AVC_SEQHDR,
+					Payload:         buf,
+				})
+				require.NoError(t, err)
+
 			case "metadata without codec id":
 				// C->S metadata
 				err = mrw.Write(&message.MsgDataAMF0{