width and height are a video's size in pixels, so the page keeps its room before the video loads. They only give the room together, so one without the other, or one that isn't a whole number of pixels, is dropped. Supply both sides. media({ size: true }) can read remote dimensions for trusted documents. A player is never wider than the page, whatever its width.
Incorrect
{width="640"}Correct
{width=1280 height=720}