Video/audio out of sync using iXpand drive with iPhone X using 4K @ 60FPS

I have been succesfully using my iXpand drive to copy 720P/1080P videos (all at 60FPS) from my iPhone X to my PC. Those videos run great right off the iXpand drive and also when I transfer them to my PC. However, last weekend I recorded a bunch of 4K @ 60FPS video. I successfully copied the video to my 128GB drive (USB 3.0) but when I play the video on my PC off the iXpand drive it plays in slow motion while the audio appears to be playing nornally. 

I deleted all my 4K video from the iXpand drive and recopied it again from my phone. Same result. I deleted it all again and then copied a single 13 minute video (also in 4K @ 60FPS) and it also plays the video in slow motion when I watched it on my PC from the iXpand drive. 

The videos all play smooth on my iPhone X, no lag, no slow motion video. They also play smooth when I transferd some to YouTube directly from my phone. 

Please help! 

My PC specs: 

Intel i7 4790K @ 4.0GHz


Windows 10


Ok, I read the other thread that was talking about issues with 4K60 FPS and I realized I wasn’t using Quicktime or Windows Media Player (WMP) to view the video on my 4K monitor. When I opened the files on WMP, the vidoes all seem to be running normally, with the out of sync issue resolved. Woot! 

I’ll leave this thread open for others who come across the same issue.  

It would be helpful to know what media player was having an issue playing the 4K files so others can avoid using it. 

It was the generic Movies and TV viewer in Windows 10 that wouldnt play 4K smoothly.