Thank you for noting that program. It is very useful. It looks like it is likely due to it being h265 and my using a Firefox-based browser: https://bugzilla.mozilla.org/show_bug.cgi?id=1332136 >"*Mozilla currently has no plans to support H.265. Our focus will be on AV1.*" >"*We will not support h265 video while its patent encumbered.*" I had re-encoded it to h264 as I selected my standard conversion profile and did not notice that it was originally h265. That is why the one I uploaded played fine in-browser and locally for me on Windows and why yours played fine locally for me but not in-browser. Apparently I've somehow managed to have never encountered an h265 video online while using this browser.