Display size and source detail are separate
A 720p source can be displayed fullscreen on a 4K panel, but the larger display area does not create original 4K detail. Likewise, a small inline player can receive a high-resolution representation. Report the source or rendition separately from the dimensions of the presentation box.
Imagine a player that works normally but returns an error when its fullscreen control is used. The source already passed some delivery and decoding checks. Preserve that success while investigating the display request; resetting the account or replacing the playlist would discard useful evidence about the actual failing stage.
User activation and frame policy matter
MDN documents transient user activation for entry and a fullscreen Permissions Policy. Embedded contexts require appropriate permission through their containing environment. A button inside a frame can therefore face a different policy from a player opened directly in its own page.
A developer should compare the actual top-level and embedded contexts, including the applicable policy and frame attributes. Adding an allow attribute is not a universal override for a more restrictive parent policy. A technical report needs the specific rejection and context rather than a claim that every iframe prevents fullscreen.
Check the transition in both directions
Observe entry, the element actually presented and exit through the normal browser mechanism. Check whether controls remain usable and whether the playback position continues. A custom interface should follow fullscreen state changes so it does not display an Exit label after the browser has already left the mode.
For a viewer report, note whether the browser's own fullscreen command and the player's fullscreen control produce different results. They may act on different targets. Keep source quality, caption position and control visibility as separate observations, because one successful display transition does not verify the entire playback experience or every accessibility requirement.
Questions about this guide
Does fullscreen prove the stream is 4 K?
No. Presentation size and source detail are separate.
Can inline video work while fullscreen is denied?
Yes. Fullscreen has additional context and permission requirements.