SD Association Reveals New UHS Speed Class 3 for 4K Video Capture

SDXC UHS-II Speed Class 3

The SD Association has a new speed class standard designed for 4K video capture. The new cards will be labeled as UHS-I or UHS-II Speed Class 3 cards, which will define them as capable of a minimum 30MB/s constant write speed.

Speed class ratings are crucial for video capture.  Because video capture data rates are critical for camera manufacturers, they will typically recommend a particular SD speed class for use when capturing video with a camera or camcorder.

UHS-I and UHS-II symbols indicate bus interface for data transfer. UHS Speed Class symbols, such as U1 and U3, indicate minimum write speeds for real-time video recording. For UHS rated cards, you will find the numeric class rating within the letter “U” on the card’s label.  (See the U3 labeling in the top image.)

Compressed 4K video capture data transfer rates will vary among cameras depending on what codec the camera uses. The new U3 Speed Class should be plenty fast enough to handle Sony’s XAVC-S 4K codec (used in the new Sony FDR-AX1), which captures 4K video at a 150Mb/s data rate. The U3 Speed Class at 30MB/s minimum write speed translates to a 240Mb/s data rate.

Of course, the particular camera will need to support the particular bus interface (e.g., UHS-I or UHS-II) of the card for the minimum data rate to be effective. Be sure to check your camera’s specs or manual for more info on supported card types.

The new Speed Class cards will be available in SDHC (4GB to 32GB) and SDXC (64GB to 2TB) card types.

Photographers need to keep in mind that the U1 and U3 ratings are practically meaningless for still photography. The max data transfer rates can vary widely among cards with the same U1 and U3 ratings.

For more about SD card types and ratings, see the resource article Demystifying SD Cards.