A couple of smartphones aside, 4K video has until recently been the preserve of pro-level equipment, and the memory cards found in most devices just can't keep up. But the next generation of SD cards will change that.
The SD Association—for such a thing does indeed exist—has announced that an Ultra High Speed Class 3 format, otherwise known as U3, will soon be available. If the name left you in any doubt, this thing should be extremely capable indeed, guaranteeing write performance of at least 30 MB/s, which is plenty to record 4K video with no glitches.
Image by StephenVelasco under Creative Commons license