Check the element renders before you blame the codec

There was a stutter on a hero video loop. I spent an embarrassingly long time on PTS frames, codec negotiation, and Chrome's hardware decoder. None of it helped — because the element wasn't rendering at certain breakpoints. A `display: none` rule from a stale media query was hiding it, and the browser was serving a fallback.

First-principles debugging means starting at the bottom of the stack: is the element on the page, is the file loading, are the bytes arriving. Theories about exotic browser internals are the *last* place to look, not the first.