Sustained Write Is The Video Specification
Video recording writes continuously, and a card that cannot sustain the required rate causes a recording to stop, which no amount of peak speed prevents.
Video speed class ratings state a guaranteed minimum sustained write rate, which is the only figure that matters for recording.
The large numbers printed on the front describe peak read speed, which affects how quickly footage copies off and nothing about whether recording works.
The Class Symbols Explained
Speed class, UHS speed class and video speed class are three overlapping systems printed as different symbols on the same card.
Video speed class, written as V followed by a number, states the guaranteed minimum sustained write in megabytes per second, which is the clearest of the three.
Device manuals state a required class, and using a card below it produces recording failures that appear intermittent and are entirely predictable.
Counterfeits Are A Real Problem
Counterfeit cards reporting a false capacity and speed are widespread on marketplace listings, and they fail catastrophically once real capacity is exceeded.
Buying from a manufacturer or a reputable retailer rather than a marketplace seller avoids most of it, and a price well below the market rate is the clearest signal.
Verification software writes and reads the full capacity to confirm a card is genuine, which is worth running on anything bought cheaply.
Bus Interface Limits
UHS-I, UHS-II and UHS-III are different bus interfaces with different maximum speeds and different physical contact arrangements.
A faster card in a slower device runs at the slower speed, which means a UHS-II card in a UHS-I camera delivers UHS-I performance.
That is not a fault and it does make the additional cost pointless unless a reader or a future device supports it.
Cards Wear Out And Fail
Memory cards have a finite write endurance and fail, frequently without warning and frequently at the worst moment.
Cards rated for continuous recording in dashcams and security cameras use higher endurance flash specifically for that reason.
Formatting in the device rather than on a computer, and replacing cards periodically rather than using them until they fail, are both standard practice.
Card readers are worth buying properly, since a cheap reader caps transfer speed regardless of how fast the card is and is a common reason for slow copying. A reader matching the card bus interface delivers the speed the card is capable of. Built-in laptop readers are frequently slower than the cards people use in them, which surprises people comparing transfer times.
Capacity is worth buying generously for recording, since a card that fills mid-session ends the recording and swapping cards is exactly what nobody wants to do while filming. Prices per gigabyte fall as capacity rises, and a larger card also spreads writes across more cells, which extends its life.
Physical card formats differ between devices, and microSD with an adapter behaves identically to full size while being far easier to lose.
The Verdict
A category where the video speed class is the only figure that matters and counterfeits are a genuine risk.
Peak speeds mislead, faster cards are wasted in slower devices, and counterfeit cards fail catastrophically.
Look for the V rating, not the headline speed. That number is what determines whether recording stops.
Auf einen Blick
Vorteile
- Video speed class guarantees sustained write
- High endurance cards suit continuous recording
- Cheap relative to the devices they serve
- Verification software confirms authenticity
Nachteile
- Headline speeds describe read, not write
- Three overlapping class systems confuse
- Counterfeits are widespread on marketplaces
- Faster cards are wasted in slower devices
Häufig gestellte Fragen
Which speed number matters?
The video speed class, written as V followed by a number, which states the guaranteed minimum sustained write. The large headline number is peak read speed, which affects copying footage off and nothing about whether recording works.
How do I avoid counterfeits?
Buy from a manufacturer or reputable retailer rather than a marketplace seller, and treat a price well below market rate as the clearest warning. Verification software that writes and reads full capacity confirms a card is genuine.
Is a faster card worth it?
Only if the device supports the bus interface. A UHS-II card in a UHS-I camera delivers UHS-I performance, which makes the extra cost pointless unless a card reader or a future device can use it.
Spezifikationen
| Type | High speed SD memory card |
| Critical figure | Video speed class, V rating |
| Headline speed | Peak read; irrelevant for recording |
| Class systems | Speed, UHS and video class |
| Check | The required class in the device manual |
| Risk | Counterfeit capacity and speed |
| Verify | Full capacity write and read software |
| Practice | Format in the device; replace periodically |
Fazit
The V rating is the number that matters. And buy from somewhere reputable — counterfeits are everywhere.
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