Re: [mediacapture-record] MediaRecorder needs to define effect of adding / removing tracks in its input MediaStream

Why cannot `MediaRecorder` record the `MediaStream` as long as the stream is `active`? If `MediaRecorder` cannot record an array of multiple `MediaStreamTrack`s, `MediaRecorder` should at least be able to record the only existing video and audio tracks within an `active` `MediaStream`.

Currently the behaviour is that `MediaRecorder` only records the first video or audio track, not the tracks added subsequently with `.addTrack()`.

For example 

```
video.addEventListener("playing", e => {

                let stream = captureStream(video);

                let tracks = stream.getTracks();

                for (let track of tracks) {
                  mediaStream.addTrack(track)
                }

                for (let track of mediaStream.getTracks()) {
                  if (tracks.find(({
                      id
                    }) => track.id === id) === undefined) {
                    mediaStream.removeTrack(track);
                  }
                }
                ..
})
```

the `MediaStream` is `active` throughout the procedure, though only the first video and audio track are recorded; tried enough times `MediaRecorder` might record only portions of one of the added tracks.

-- 
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Received on Saturday, 17 March 2018 16:10:12 UTC