Hey guys, I fixed the issue. It wasn't a video codec issue or anything. I think it had something to do with me switching up the directories after gameex downloaded the artwork. I ended up doing a clean install and kept all the default directories ans it's working now,
Thanks for all the help!
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I thought the fresh install is what fixed my issue with the themes and preview videos but that's not the case. After I got everything up and running I turned filters off in setup wizard to try to gain access to 2p versions of 4 player games like tmnt. When I did that all the themes stopped working. I turned the filter back on and all my themes showed up again.