Make Track an interface

[at-wat]

To deal with a MediaStreamTrack coming from an another package like pion/mediadevices, Track would be better to be an interface something like:

type Track interface {
  ID() string
}
type LocalTrack interface {
  Track
  ReadRTP() (*rtp.Packet, error)
  ...
}
type RemoteTrack interface {
  Track
  WriteRTP(*rtp.Packet) error
  ...
}
type RTPSender interface {
  ReplaceTrack(LocalTrack) error
}
type RTPReceiver interface {
  ReplaceTrack(RemoteTrack) error
}

ref: pion/mediadevices#39 (comment)

It might require a lot of breaking changes, so it would be a v3 matter.

[Sean-Der]

@at-wat 👍, my goal is to publish a new release this weekend. Then feel free to break anything/everything you want in master :)

If you wouldn't mind adding stuff to https://github.com/pion/webrtc/wiki/PlanningV3 that would be really helpful. I want to make sure our new changes interact well with.

• Better Stats
• NACK
• Congestion Control
• SVC/Simulcast

All of these are hurt by the current API. So would be awesome if we get it right the first time :)

[Sean-Der]

I am covering here https://github.com/pion/webrtc/projects/17

/v3 has been complicated because of all the use cases I am trying to cover. I am sure we will come to a good solution, but need to get it all into one place.