As you can see here, everything is working well in another site; same video, poster image, logo and player setup (responsive).
That means that there is something responsible of that, your theme or a plugin.
Usually the best way to find out the guilty, is to deactivate all the plugins and activate them one by one. Also, if this was not resolutive, move to another theme could be a useful test, something like Twenty Fifteen or another default theme will be fine.
Hope this helps; please keep me informed, ok?