Required vs optional track fields

[kixelated]

Because of the intermingling of track types, every track field is optional. This is pretty annoying from a type safety point of view, because it means that your code needs to account for a potential null at every field. ex. it would be valid for a track to have a height but not width, or mix video fields with audio fields.

It would be nice to specify the base functionality for a track type. Like an audio track MUST have a codec and sample rate, instead of leaving everything optional.