SD card write speeds for movies

Hi folks, apologies if the following is well known, but I'd been hunting around for a while for some official recommendations re. SDHC write speeds / class for the 60D, esp. for recording movies, found this:

http://cpn.canon-europe.com/content/education/tipsandtricks/2324.do?filter=eos60d

"SD card write speeds for EOS Movie files

If you plan on shooting EOS Movies with Canon’s EOS-1D Mark IV, EOS 550D or EOS 60D DSLRs using SD cards as your main storage medium, you’ll need to make sure the cards you use are fast enough. All of these cameras need a minimum write speed of 8Mbits per second (MB/s). While this seems quite low, with many cards boasting speeds much higher than this, the camera needs a sustained write speed rather than a burst rate. SD cards are often labelled with both a ‘Class’ rating and an ‘MB/s’ rating. The MB/s rating is a burst transfer rate, while the Class rating refers to minimum sustained writing speed. For example, a Class 6 SD card has a burst transfer rate of 48MB/s, but a minimum sustained write speed of just 6MB/s. Because of the need for a sustained writing speed, you’ll need to find cards that are Class 8 or faster to ensure that you don’t run out of camera buffer while shooting EOS Movies. "

Hope this helps.

That advice is sound, except for the confusion between megabits (Mbits) and megabytes (MB). If you divide 4GB into 12 minutes, you'll find that the average data rate of the video is around 5.7 MB/s. A sustained write of 8 megabits per second (1MB/s) is not going to work for HD video, whereas 8 Megabytes per second would cover it.

That said, the class ratings are minimum requirements, so it's entirely possible that one brand of Class 6 card will work, whereas another brand will not. In theory, any Class 10 card should work, if the manufacturers are honest with their ratings. In practice I bought the Class 10 sandisk card because it's reported to work fine by many users.

You're mixing up the abbreviations. Mbps is the proper shortening of megabits per second, and MB/s (capital B) is megabytes per second.

Secondly, in the 60D manual, it says class 6 or higher, which is sufficient. 6 megabytes per second (6 MB/s) is greater than the 5.5 MB/s output of the camera (330 megabytes per minute divided by 60 minutes per second). I have no trouble with my class 6 card in my 60D when recording video. However, I wonder if the camera would be able to clear its buffer faster if I had a class 10 card.

Thanks, you are both entirely correct of course re. the Mbps versus MBps. The text in the OP was pasted directly from the Canon website I noted the same and should have corrected this before pasting. Appreciate the advice re. brand and rating, believe I've seen some reports that the Transcend cards often do not live up to the class rating, whereas Sandisk appear a safer bet.

I have a Class 4 PNY Optima 8GB SDHC card, and I am able to record 1080p without the camera stopping it, unlike my Class 6 Adata 16GB SDHC, which stops recording after a few seconds. Thus, I have little trust in classifications. I'd stick to anecdotal evidence in this case, what works for other people will work for you. Buy trusted brands.

hahncholo said:

I have a Class 4 PNY Optima 8GB SDHC card, and I am able to record 1080p without the camera stopping it, unlike my Class 6 Adata 16GB SDHC, which stops recording after a few seconds. Thus, I have little trust in classifications. I'd stick to anecdotal evidence in this case, what works for other people will work for you. Buy trusted brands.

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In that case it makes a mockery of the so-called "class" rating system for SD cards.

Don't forget that the image size of an HD movie frame is only a fraction of a still image (about 2GB), so it's bound to write to the card faster.
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hahncholo said:

Photographers feel guilty that all they do for a living is press a button. - Andy Warhol

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Class ratings are not as important as the manufacturer stating the R/W speed. SanDisk warranties for life and publishes there R/W speed on the packaging.

A SanDisk Extreme III at 30mb/sec is a very desirable SD card. Write speeds is all that matters, other brandings like HD Movie is marketing. It doesn't matter what your are writing to the card, movies, stills, PDF's.... how fast it can transfer data is all you have to be concerned about.