It is unclear whether a track that has received zero frames so far ( and it does not know the size of video frames to come) should expose width, height and aspectRatio.

According my testing:

• receiver tracks start with no width, height and aspectRatio.
• canvas capture tracks may start with width:0 in Firefox but not in Chrome.

If height is zero, either aspectRatio is NaN or it should be undefined.

It would be good to make things consistent across browsers.