4k and SD Card Speed

N

neweditor

Well-known member
So I'm getting into 4k shooting and I was wondering about the necessity of read/write speed for the various SDXC cards out there. I know that for RAW photography a high read/write is helpful, but I'm really not sure how they apply to the video world.

For instance, right now on BH there are the following cards:

SanDisk Extreme Pro 256gb Class 10 UHS 3 - 95 read/90 write for $199 http://www.bhphotovideo.com/c/produ..._sdsdxp_256g_a46_256gb_extreme_pro_uhs_i.html
Lexar 256gb Class 10 UHS 3 - 95 read/45 write for $109 http://www.bhphotovideo.com/c/product/1131706-REG/lexar_lsd256cbnl633_lexar.html
PNY Technlogies 256gb Class 10 UHS 1 - 90 read/60 write for $90 http://www.bhphotovideo.com/c/produ...sdx256u1h_ge_256gb_elite_sdxc_uhs_1_card.html

Keep in mind this is for 4k video generally shot XAVCS @ 100 mbps

Other than the last card being UHS 1 rather than 3 (still fuzzy on the main difference there as well), is the write speed of 45 on the Lexar vs. 90 on the SanDisk such a big deal when it comes to video? Is the extra maximum write speed worthy of $90 extra per card? What makes the first SanDisk card so much more valuable? (nearly double the price)

Thanks in advance!
 
The read and write speeds are usually something bordering on lies. Read it carefully and you'll see that it usually says something on the order of "write speeds UP TO 95mbps" or something. Well, yeah, sure, it might go up to 95, but it also might run at 30mbps too, right? A prudent shopper would ignore such claims. The "Class 10" or "UHS 3" designations are far more reliable indicators of actual card performance. The "Class" and "UHS" standards specify a MINIMUM SUSTAINED speed, not some pie-in-the-sky potential top speed. When it comes to video, you need a card that can sustain the minimum data rate your camera requires.

Your camera manual should make recommendations as to what to use. In the Panasonic 4K camera, they specify that for 100mbps-200mbps footage, it requires a UHS 3 card. You may or may not be able to get away with recording on a slower card, but it's a fool's choice, because sooner or later some hiccup is going to happen and bite you in the butt when you can least afford it to. I can't imagine the XAVCS would require more than a UHS 3 card.

In SDHC cards, they are rated by "Class"; the higher the number, the faster the card, up to Class 10. In SDXC cards, they use "Class", but that's an older term; the newer cards are UHS (Ultra High Speed) and they are designated by number, with UHS 1 being the slowest of the UHS speeds, and UHS 3 being notably faster.

And yes, there's a world of difference between the still photographer (who's perhaps dumping a burst of 12 or 15 gigantic 20-megapixel raw images all at once) and the video shooter, who's recording a maximum of maybe 200 megabits per second. If your Sony camera's manual says that it works with UHS 3, then either that SanDisk or Lexar should work fine. For the still photographer, the extra write speed may indeed be worth more, but I doubt sincerely that the video shooter will see a difference in performance.
 
Barry_Green said:
The "Class 10" or "UHS 3" designations are far more reliable indicators of actual card performance.
Click to expand...

When Class 10 SD cards first came out ( a long time ago ) I found that some brands had trouble managing the 24 Mbps video stream from my camera, so I quickly learned which brands were reliable for me. ( over the course of a year I tried at least 8 different brands of SD cards that showed a wide range of results )

If you're running a Windows PC I recommend using the free ATTO Disk bench to see what the real read and write speeds are for your SD cards, though you will need to use a USB3 card reader and USB3 PC port as many of today's cards will exceed the typical 35+ MB/sec speed of a USB2 reader and port. My three year old SanDisk Class 10 SDXC UHS-1 95MB/sec cards show a maximum write speed of 80+ MB/sec, but I've had older SD Class 10 cards that had trouble reaching 10 MB/sec. ( I promptly threw these cards in the trash )
 
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