What class memory card do I need for HD video?

With the introduction of the new Class system for memory cards, it has become a little bit confusling (yeah that's one of my words, use it if you like but please place a gold coin in the tin) as to just how fast a card really is.

With the normal (old) method of 80x 133x 266x etc, it is easy to see that one card is faster than the other, but what does Class 6 or Class 10 mean? Is the bigger number faster or is the bigger number slower?

When we think of the term "class", we have become accustomed to thinking that 1st Class (ie; "1") is best. 1st Class on an aircraft or a Canon EOS 1 just to name a couple. Well the Class system for SD cards is the other way around and the higher the class number, the faster the card.

Why have they gone against convention then? I hear you ask.

Well there is a very simple answer.... The class actually refers the minimum write speed of the card in MB/sec & not a general quality grading that we are use to with the term.

Cards are getting faster all the time. Technology is moving at an incredible rate and the manufacturers just keep finding new ways to get more and more speed out of a bit of silicon.

With this in mind, there can be no "locked in" general grading. If we called today's best cards Class 1, what do we call tomorrow's? To call them Class 1 also, would mean the that an older card is now incorrectly labeled and would no longer give the user an accurate representation of it's true speed.

So we simply have to go with the card's minimum write speed and forget about any of our previous interpretations of the term "class". This allows a card's rating to faithfully represent it's minimum write speed and allows the user to make an informed choice, given the intended use.

OK, so cut to the chase.... What card do we need for video?

Looking at the various brands, one could arrive at the conclusion that Class 6 is a video rated card. Many manufactures will have the HDVid logo on Class 6 cards and some, will even display the time length of HD video that the card can record.

Herein lies a problem. What is HD video?

"High-definition video or HD video refers to any video system of higher resolution than standard-definition (SD) video, and most commonly involves display resolutions of 1,280×720 pixels (720p) or 1,920×1,080 pixels (1080i/1080p)" - Wikipedia

So from this we see that HD video is in fact a sliding scale. Are the manufacturers labeling their cards as suitable for recording HD at 1,280×720 or 1,920×1,080 pixels? From my personal experience, I think they may be using 1,280×720 as their standard for HD. This means that while a Class 6 card may be perfectly suitable for recording HD at 1,280×720, it may struggle with 1,920×1,080.

Why do I say this? Well my camera is capable of shooting at both HD (1,280×720) and FullHD (1,920×1,080) and when shooting a constantly moving subject, you can see the difference. Let's use a waterfall as an example.... Using a Class 6 card and shooting HD the water flows smoothly over the screen for the entire length of a 5 minute grab.

Switch to FullHD and every so often the smooth flow of the water has a momentary stutter. It's just freezes for a fraction of a second, as if the card has reached it's load capacity and takes a quick break to grab some air.

Repeat the very same experiment as above with a faster Class 10 card and FullHD remains smooth just the same as the lower res HD.

So the answer to our original question is in fact another question.....

Qu: What Class card do I need for HD video?
Ans: What resolution HD video are you shooting? Because 720HD will be fine with a Class 6 card, while 1080HD would be better with a Class 10, especially when moving subjects are involved.

Cheers

Rusty
AustralianLight - Landscape Photography

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