If you didn't know already, you should know that the LG G3 sports a 4K display. Although the "4K" categorization comes with an asterik, it is still one of the sharpest, most vivid displays that you will find on a mobile device. The problem is that there is not a whole lot of 4K content available for the G3 or other 4K devices in general, so it's a bit of a challenge to REALLY see the 4K imagery.
YOUTUBE: Your easiest (and least costly) option should be YouTube. You can search for 4K videos, and it should generate a list of a few thousand (or million) results of 4K videos. The one that almost always shows up at the top of that search for me is the video entitled Road to Machu Picchu - Peru in 4K - YouTube.
Here is the issue with the 4K as seen on the LG G3 - it is limited to 30 fps. If you are accustomed to video gaming on any handheld device, or you have a large format 4K screen already, then you will see this video and other native 4K videos as choppy because of the 30 fps. Even though the image clarity will be exquisite, you may be distracted by the choppiness of the video.
So what are other alternatives?
Netflix, or similar streaming options (Hulu plus, HBO Go, Comcast Streampix, Vudu, etc.) are the second option, only because they have a nominal cost associated with their subscription ($5-$15 per month?). Netflix offers some UltraHD and 4K content (as I imagine the others do as well), but I can't recall which videos are available as UltraHD for mobile devices. I know that 4K/UHD titles on Netflix are few and far between, BUT this should not assuage you from subscribing to or using Netflix. Even full HD video on the G3 looks amazing. Check out ANY of the Transformers series, or even the new Star Trek flick to see how it looks on the G3.
Finally, you can go to the dark side and sideload something like Popcorn Time. My understanding with this app has been that the quality of the video is generally either 720p or 1080p, but looks phenomenal on the G3. I have not yet heard about any 4K videos on Popcorn Time, but I have not done much searching. The PROBLEM with Popcorn time is that it streams crowd-sourced torrents, which may not be the most legal thing to do. If you want to avoid any legal ramifications, you may want to stay away from this one, albeit it may well provide you with the best viewing (and selection) option.
Most importantly, I MUST stress the limitations of the frames per second (fps) on the G3. When viewing 4K, it is limited to 30 fps, so you may actually have a smoother viewing experience with video that is 1080p, even though the level of definition may only be 1/4 of a 4K dispaly. However... it's still going to look amazing, especially on a screen this size.
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