When it comes to shooting 4K video, there are four things that really matter: card capacity, write speed, data transfer speed, and video speed. And three of them revolve around the same metric. For this discussion, we will be referring to standard-size SD cards and microSD cards.
1. Card capacity: You already know that shooting 4K video leads to excessively large files. We just mentioned that an hour of 4K video uses about 45GB of storage space. Start with 63GB unless you are shooting way less than an hour or are not concerned about running out of space. Card capacities can range up to 256GB and are ideal for 4K video.
2. Write speed: This is probably the most critical factor in selecting 4K storage. Your card choice must have a fast enough write speed to keep up with incoming data. But the choice is easy. SD cards have six different speed classes. Only the U3 class is capable of writing at the speed required for 4K video which is 30MB/s. Choose only cards that have the U3 marking (The number 3 inside a capital U).
3. Data transfer speed: Pairing your U3-rated SD card with compatible devices that support the UHS bus interface will possibly boost the transfer speeds of your card. Most cameras support the UHS bus interface that the UHS memory cards can take advantage of. Bus interfaces are available in two speeds which are UHS-I and UHS-II. UHS-I have theoretical transfer speeds of up to 104MB/s while the UHS-II interface can have theoretical transfer speeds of up to 312MB/s. For U1 and U3 rated SD cards, only the UHS-I bus interface is compatible while the UHS-II is used by the Video Speed Class memory cards.
4. Video speed: SD memory cards for 4K video storage should at least have a V30 rating/marking meaning it has the minimum continuous write speed of 30MBs required for 4K. SD cards with Video Speed Class ratings are specifically meant to capture and store video resolutions in 4K or 8K. As the UHS-I bus interface can only support V6 to V30 , the UHS-II bus interface supports V6 to V90 speed class memory cards. The V90 is used in UHS-II mode or faster.
If you’re looking for the best SD card performance you can get for your 4K video, look for UHS-II cards with a V90 rating.
These are all great solutions to the UHS speed class SD cards if your camera requires higher write speeds when recording in 4K or 8K resolution. Having fast enough SD cards with the right write speeds is important so check with your device owner’s manual to see the required specs for your memory card storage.
Helpful Tip: Your capacity choice should be twice as large as what you normally use in 1080p recordings, and the three-speed categories (write, data transfer, and video speed) are each based on the 30MBs required for 4K recording.
If you need further help in choosing the correct memory card for 4K video, check out our helpful guide explaining the speed classes and write speeds of all our memory cards here.
From: https://www.kingston.com/en/blog/personal-storage/choose-storage-4k
