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AFAICT the <video>.width/height DOM attributes don't have default values defines as far as reflecting attributes go, and so getting .width or .height will return 0 when the content attributes aren't there (or won't parse). This seems unhelpful. We think the width/height DOM attributes should return the rendered width/height of the element, if it's being rendered, or else the intristic width/height of the video element's playback area.
For example, width should be 100% of parent width (see CSS) and height 100%*3/4 of parent width.
If you want the video dimensions, use videoWidth and videoHeight. If you want the dimensions of the rendering, use the CSS object model (clientHeight, etc). As a general rule, the DOM attributes don't return values other than what the content attributes have. There are some exceptions, like Image.height, but I think we want to keep the platform as consistent as possible.