Allow calling `track.restart()` on local tracks created using constructors

[jpodwys]

Twilio employee Donal Toomey requested that I create this issue.

Today, calling const videoTrack = new LocalVideoTrack(mediaStreamTrack) results in being unable to call videoTrack.restart(). Today, we're bypassing this by passing the following into the constructor's options object.

// @ts-ignore
isCreatedByCreateLocalTracks: true,

We'd like to request one of the following two solutions

1. Allow calling track.restart() on local tracks created via constructors (this is our preferred solution)
2. Make isCreatedByCreateLocalTracks public (this is a reasonable fallback solution)

[jpodwys]

@donaltoomey is there any update here?

[luisrivas]

Hi @jpodwys, could you please elaborate on your use cases? We only support restarting local media tracks because we know how to reacquire them using getUserMedia(). For other tracks, we cannot determine how they were created.

[jpodwys]

Hi, thank you for the response!

We only call track.restart(constraints) when switching devices. With that in mind, we always provide constraints. Perhaps a reasonable update would be to allow local tracks created via constructors to call restart so long as constraints are provided. If, however, constraints is absent, throw an error.

[luisrivas]

Thank you for the feedback. We will review your comments and get back to you.

Out of curiosity, why do you prefer acquiring the track and calling the new LocalVideoTrack instead of using the createLocalTracks method?

[jpodwys]

Great question!
We support local and remote control of PTZ cameras and we use the track.name field to inform remote participants that a track is of type PTZ. However, even when we provide PTZ in our constraints object, we can't know for certain whether a MediaStreamTrack supports PTZ until after we've acquired it.

Manually acquiring the track allows us to determine whether it's a PTZ-capable track prior to creating a LocalVideoTrack. This is important because the LocalVideoTrack constructor requires a name property.

If we used createLocalTracks, we would have to provide the track's name before acquiring the underlying MediaStreamTrack and therefore before knowing whether the track supports PTZ.