4K video playback is slow

[wookiee2cu]

Hello, new to Androids and have a quick question. So I have messed around a little bit with setting the video recording to 4K and just shot a short clip just to see it in action. When I play the video back it seems to play back in slow motion and the radio that was playing in the background seems to cut out for about half a second every few seconds. Is this because the file size is so large and the phone is struggling to play it back? It was only like a 8 second video so I wouldn't think that would be the case, if it was a 4 minute video then I could possibly see that happening. Anyone else seeing this on their device?

Also I saw a video clip (I think it was the M8) and they were showing a demo of shooting in 4K and then they could edit it and you could adjust portions of the time line to go to slow motion and then back to standard motion, is this possible with the S5 4K video? Thanks for any tips/suggestions you may have!