There is one technical challenge that some people experience when shooting video at 4K. Cameras that shoot Ultra HD 4K video require memory cards with faster write speeds than when shooting normal 1080p Full HD video.

When memory cards can’t write the video data fast enough it causes the camera to just stop recording. The problem can also also be caused by a combination of the camera‚Äôs buffer being too small and the memory card not being able to record the data it receives from the camera buffer fast enough in order to keep the camera capturing more video data smoothly. And when a camera that shoots 4K has buffer issues, it becomes even more important to be using memory cards with very fast write speeds.

Many people are using standard CF memory cards like these SanDisk Extreme 64GB Compact Flash Cards or standard SD memory cards that are rated with an average of 60MB to 90MB per second data speeds like these SanDisk Extreme 64GB SDXC UHS-I cards. Cards like these are fast enough for most 1080p video shooting, bursts of still photos shot in RAW up to around 36MP, and for some 4K video recording at 24 frames per second. But often they aren’t fast enough if you want to shoot 4K video at 30-60 frames per second.

With some Sony mirrorless cameras, memory card speed issues can be less of a problem at times since Sony uses a codec when recording 4K video that compresses video files more than some of the other camera brands. 4K video shot with the newest Canon 5D Mark IV DSLR camera however is a good example of where you can easily run into buffer and memory card problems. The 5D Mark IV shooting 4K video at 30 frames per second captures around 60 megabytes per second of video data. Although it sounds like SD cards that are rated at 90MB per second should be enough for a camera shooting 60MB of video per second, they aren’t.

The problem is that the actual write speeds of most memory cards are usually only half, or at most, two thirds of the rated speeds that are printed on the face of the memory cards. This is because the stated card speeds are normally read speeds and not write speeds. So card manufacturers can be tricky when disclosing their card speeds.

As proof of this, I recently experienced camera shut downs after just 5 seconds when using the SanDisk Extreme 64GB SD cards (rated at 90MB per second) to record 4K video with my Canon 5D Mark IV. I also experienced camera shut downs with the SanDisk Extreme 64GB CF Cards on 4K video with my Canon 5D Mark IV, even though these CF cards are rated with write speeds of 85MB per second. This can all be disruptive on a shoot to say the least.

The simple solution to avoid any card speed write problems is to get yourself an SD memory card that states the speeds are up to 300 megabytes per second. Even if they only write at half that, data writing issues while shooting 4K video will be fully resolved. The best option would be the SanDisk 64GB SDXC UHS-2 300MB/s Extreme PRO cards because of their super fast write speeds, high level of reliability, and Sandisk’s great warranty coverage.

But before buying one of these memory cards make sure that your camera model is compatible with the newer UHS-2 SD card format. If your camera doesn’t support UHS-2 cards then the next best thing are the SanDisk Extreme PRO 64GB SDXC UHS-I 95MB/s memory cards here.

The Canon 5D Mark IV will run UHS-2 cards, but not at the card’s full speed capability. So the camera really only supports up to UHS-1 speeds. Once I switched from the SanDisk 90MB/s Extreme cards to using the SanDisk 95MB/s Extreme PRO cards, thankfully I have had no more 4K video recording problems on my Canon 5D Mark IV.

If your camera requires a Compact Flash card for recording 4K video (the Canon 5D Mark IV also uses CF cards) then I would recommend the Sandisk 64GB Extreme PRO UDMA 7 CF Cards, which SanDisk says records data at up 150MB per second. I have tested this model of CF card on my Canon 5D Mark IV shooting 4K video and no problems.

There are also other brands like Delkin, Sony, Transcend, Lexar, Kingston, and others which make memory cards that can also write at high speed. But warranty coverage with SanDisk is worldwide and they will send replacement cards to you no matter what country you are located in.

I once had an experience with Lexar and a CF card that failed. Lexar told me they would only send a replacement card to me at an address in the USA, which is a problem since I reside outside the USA.

So now I only buy SanDisk. Plus I often travel to shoot video in other countries, and we all know that card failures can happen anywhere. If you are like me then you may also be best to stick with SanDisk cards. SanDisk is now a subsidiary of Western Digital (as of May 2016), which is the same company that makes a lot of the internal and external hard drives used with many of today’s computers.

If you have any questions, comments, or experiences of your own that you would like to share about memory cards and write speeds when shooting 4K video then please feel free to post them below.