SD card speed class
Also known as: V30, V60, U3, UHS-I, video speed class
Ratings such as V30, U3 or V60 on memory cards that promise a minimum sustained write speed, which high-bitrate video recording needs to avoid dropped frames.
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What it means
Video recording writes data continuously, and the card must keep up without pausing. Speed class markings promise a minimum sustained write speed. U3 and V30 guarantee at least 30 MB per second, V60 at least 60 MB per second, and V90 at least 90 MB per second.
Those numbers relate directly to Bitrate. A camera recording at 100 Mbps writes about 12.5 MB per second, which V30 handles comfortably. Higher bitrate modes, All-Intra codecs and some high frame rate settings need faster cards.
The big read speeds printed on packaging are a different number. They describe how fast the card copies to a computer, not how reliably it records.
How it works in practice
Check the camera manual for the recommended card class and use a reputable brand. Action cameras typically recommend V30 or faster. Drones and cameras with very high bitrate modes may need V60 or V90.
Use several medium cards instead of one huge card. If a card fails or gets lost, you lose less, and you can rotate cards during a trip while backing up the full ones each evening to a laptop or cloud backup.
Format cards in the camera regularly, and retire cards that start throwing errors, however much space is left on them.
What to watch out for
Counterfeit cards are common, especially from marketplace sellers. They may report a large capacity or fast class but fail under sustained writes, causing dropped frames or corrupted files. Buy from trusted retailers and test new cards with a long recording.
A slow card often shows up as recording that stops on its own, a camera warning, or files with glitches. Before blaming the camera, try a known fast card.
Cards also wear out over time and are sensitive to heat and moisture. Replace old cards before an important trip, and store them in a case rather than loose in a pocket with keys, which can lead to corrupted frames from damaged contacts.
How RawClip handles it
A reliable card gives you complete, glitch-free files to upload. Copy the clips off the card, upload them to RawClip in one order, and the AI picks the best moments for your highlight.