Videos from sports cameras, drones, and 4K DSLR camcorders are a mish-mash of unusual video types, high resolutions, bit rate and frame rates, which causes problems playing videos on iPhone and iPad. For example, GoPro and DJI videos are often recorded in 4K/2.7K with 60pfs or slow-mo 2.7K/1080P with 120fps, 240fps, etc. On the one hand, these videos result in extremely large file size that iPhone (especially the space-constrained models) needs more space and harder time to cope with, while on the other hand, the videos with higher resolution consume much more resources such as processor, graphic memory and RAM than those shot in lower resolution. Consequently, some iPhone will end up with lagging and stuttering when playing these video files.
Currently, neither Android nor iPhone supports the playback of 4K 4:3 videos taken with GoPro. If you want to play them, you need to use the QuikStories to downscale it or manually do that. While recordings from 4K DSLR cameras are always saved in formats like R3D, MXF, ProRes, AW1, XAVC, AVCHD, AVI, MP4, and others iPhone won't accept. No matter how complicated the video settings are, you can convert unsupported videos to iPhone with VideoProc, which is designed for 4K UHD videos with flawless support for 370+ input codecs.
Step 1: Free download VideoProc and launch it. Then click Video from the main interface.
Step 2: Now click the +Video button and import any videos that can't be imported/loaded to iPhone. For example, transfer GoPro videos to iPhone.
Step 3: Check if the videos are in any of the iPhone supported formats listed above. If not, select H.264 or H.265 from the bottom Target Format toolbar.

Step 4: Adjust the resolution and frame rate. For example, the GoPro 1080P 120fps will not play smoothly on iPhone the highest playback frame rate is 60fps. Click the Option button to enter the video settings page. Find the Frame Rate dropdown menu and select an iPhone acceptable frame rate.
Step 5: Click Run to convert videos to iPhone now. The built-in Level-3 Hardware Acceleration tech allows the 4K iPhone video converter to process DSLR/DJI/GoPro 4K or uncompressed videos with super fast speed.