My video project is HD-vertical (1080x1920). After exporting it as an mp4 by using the settings Computer and H.264 Better Quality at the export prompt, I see that the resolution of the exported video has downgraded without warning to 608x1080 - although the Resolution in the export prompt itself was listed as 1080x1920! I'm having to use a third-party mov-to-mp4 converter (like the online Adobe Premier converter) as a workaround to maintain 1080x1920. How do I get FCP to export mp4s in the set resolution?

Hi - A few quick searches turned up just that suggestion that it might be an export bug and the recommendation to re-select the desired resolution when exporting as a workaround. I didn't see any more definitive answers regarding exporting at the wrong resolution, though apparently there are plenty of questions on FCP export issues/limitations, and a number of responses suggested using a separate converter to get the desired resolution as you did.. I'm an audio guy myself [I don't have FCP here to test] so I can't advise, but I've attached a link to a FCP course on finishing/exporting from FCP to this thread [More Info, above] -- it seems to have a lot of discussion on export options and customizing export settings, so maybe there'll be something helpful there, or perhaps a regular FCP user/guru will weigh in with a suggestion..

Wow, thanks, this worked! Since on the prompt dropdown it was already set as 1080x1920, I changed the dropdown value to 720x1280, then back to 1080x1920, before exporting. Immediately I saw that the estimated size was significantly greater than before the switch. And it worked - exported resolution was vertical-HD. Reported the bug to Apple. Thanks again.