Design of Track interface

[at-wat]

In v2, Track internally handled RTP packets.
However, according to the WebRTC API spec, codec specific processing is done in RTPSender/RTPReceiver. (ref: #9) It means Track handles only raw media data?

[at-wat]

On pion/webrtc, we don't want to put media encoder/decoder into RTPSender/RTPReceiver unlike JavaScript WebAPI seems doing.
I think we need to define

type LocalRTPTrack interface {
  rtpengine.Reader // #11 
  SetParameters(RTPParameters) // RTPSender.SetParameters() will call this.
}
type RemoteRTPTrack interface {
  rtpengine.Writer // #11 
  Parameters() RTPParameters // It will call RTPReceiver.Parameters().
}
type RTPTrack interface {
  LocalRTPTrack
  RemoteRTPTrack
}

instead of Track to passthrough the RTPSender/RTPReceiver.
Then, mediadevices.Track can receive encoding parameters and also can receive RTCP packet like PLI (and force adding a keyframe).

For SFU usage, we just have to pipe RemoteRTPTrack to LocalRTPTrack.

[at-wat]

Sample based interface would be like:

package media

import (
	"time"

	"github.com/pion/webrtc-v3-design/rtpengine"
)

// Sample represents raw media data with media duration.
type Sample struct {
	Data     []byte
	Duration time.Duration
}

// ReadSample reads Sample from rtpengine.Reader.
func ReadSample(r rtpengine.Reader) (Sample, error) {
}

// WriteSample writes Sample to rtpengine.Writer.
func WriteSample(r rtpengine.Writer, s Sample) error {
}

[at-wat]

As reported in pion/rtp#69, roundtrip transformation rtp.Packet -> Sample -> rtp.Packet loose some RTP header flags.