pion中的TrackRemote
Howard Yin 2021-09-21 03:13:04 WebRTC设计思路编程框架pion实操
上接《pion中的TrackLocal》，有TrackLocal表示表示本地发往远端的track，对应的自然也会有TrackRemote表示远端发到本地的track：
// TrackRemote represents a single inbound source of media
type TrackRemote struct {
mu sync.RWMutex
id string
streamID string
payloadType PayloadType
kind RTPCodecType
ssrc SSRC
codec RTPCodecParameters
params RTPParameters
rid string
receiver *RTPReceiver
peeked []byte
peekedAttributes interceptor.Attributes
}
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TrackRemote就没有像TrackLocal做成接口了，大概是因为参数和数据都是对面给的，用户只需要读取，不需要什么其他侵入pion内部的操作。
那么最核心的就是这个Read和ReadRTP了，就是读取数据，不必多讲。
// Read reads data from the track.
func (t *TrackRemote) Read(b []byte) (n int, attributes interceptor.Attributes, err error) {
...
}
// ReadRTP is a convenience method that wraps Read and unmarshals for you.
func (t *TrackRemote) ReadRTP() (*rtp.Packet, interceptor.Attributes, error) {
b := make([]byte, t.receiver.api.settingEngine.getReceiveMTU())
i, attributes, err := t.Read(b)
if err != nil {
return nil, nil, err
}
r := &rtp.Packet{}
if err := r.Unmarshal(b[:i]); err != nil {
return nil, nil, err
}
return r, attributes, nil
}
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因为不需要用户自定义什么操作，所以也没有什么继承之类的操作，TrackRemote本身也不需要用户自己去构造，都是在框架里构造好的。
用户要做的最主要的操作就是在OnTrack里面，当有track连接进来时处理之，比如在《用实例学习pion - gocv-receive》里面就是：
// Set a handler for when a new remote track starts, this handler copies inbound RTP packets,
// replaces the SSRC and sends them back
peerConnection.OnTrack(func(track *webrtc.TrackRemote, receiver *webrtc.RTPReceiver) {
// Send a PLI on an interval so that the publisher is pushing a keyframe every rtcpPLIInterval
go func() {
ticker := time.NewTicker(time.Second * 3)
for range ticker.C {
errSend := peerConnection.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{MediaSSRC: uint32(track.SSRC())}})
if errSend != nil {
fmt.Println(errSend)
}
}
}()
fmt.Printf("Track has started, of type %d: %s \n", track.PayloadType(), track.Codec().RTPCodecCapability.MimeType)
for {
// Read RTP packets being sent to Pion
rtp, _, readErr := track.ReadRTP()
if readErr != nil {
panic(readErr)
}
if ivfWriterErr := ivfWriter.WriteRTP(rtp); ivfWriterErr != nil {
panic(ivfWriterErr)
}
}
})
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OnTrack里面直接一个死循环不断用track.ReadRTP读数据拿去ivfWriter.WriteRTP处理。