Why can I use a 95mb/s SD card to record 200mb/s video?

S

SolidBrowser

New member
I am trying to understand why and how the camera allows me to record 200mb/s video onto a 95mb/s card?
Is this an error internally in the camera or is there something I am missing.
I have recently bought a SDXC USHII 300Mb/s card so I can record 4k video - all intra, v-long - internally.
But how can a card that says the write speed is 95mb/s write 200mb/s?
Does it actually write 200mb/s or does it just use that "option" and compress the files?
 
If there is 8Megabits per 1Megabyte, then why do SD cards offer 95megabytes per second?
It seems excessive especially since the majority of cameras that have SD card slots film under 400 megabites per second?
In this case, what would a SDXC USHII 300megabytes be useful for? Why do they make them?
 
It's marketing based on current branding competition.

It's been like this for a while and at some point 10 or so years ago, companies decided to display their specs (or not) to compete with each other. The companies that made better/faster cards proudly provided you the READ and WRITE speed while some just displayed the read speed with an asterisk to indicate that the write speed was actually lower (hence slower and not as good, but still usable for many applications). This is still practiced today.

As far as I know, only Blackmagic products seem to be able to get close (but not that close) to 300 MB/s...and that is a very high speed (most cards don't provide that).

4K/60p (DCI) ProRes 422 HQ on the Pocket or UMP is 1886 Mbps. I haven't followed the cameras closely enough to tell you if it's possible to record that on SDXC cards (instead of CFast) without dropping frames, but that would get you pretty close with about 236 MB/s. You do also want some headroom as well.

As mentioned, my assumption is that they make these fast cards because they have to if someone else already did, and the technology and knowledge is readily available so why not.
 
There's also a difference in read/write speed between burst and continuous read/write. For example, a card might have a burst write speed of 95 megabytes per second, but a continuous write speed of only 30 megabytes per second.
 
At first I didn't like the V30, V60 and V90 ratings and then on top of that, we had to figure out what VPG-130 was all about with CFast 2.0 for the C200, Arris, etc. But now, after living with it for a year or two, it's fine, although inconsistent. The manual for the Fuji X-T3 recommends a V60 card, minimum to record the 400Mbps 4K 60p with Intraframe recording, but I've read other sources say you need a V90 card to do so. I bought the ProGrade V60s and so far, no issues recording 4K 60p so it becomes a bit muddled these days. Like most thing computer though, faster is usually (not not always) better.
 
SolidBrowser said:
If there is 8Megabits per 1Megabyte, then why do SD cards offer 95megabytes per second?
It seems excessive especially since the majority of cameras that have SD card slots film under 400 megabites per second?
In this case, what would a SDXC USHII 300megabytes be useful for? Why do they make them?
Click to expand...

And still, 95 MB/s is barely enough if you want to shoot 4k RAW with the p4k, even at 4:1 and sticking to 24fps.
They sell those cards because some people need them.
 
The manufacturers have been putting out confusing data for years and years and years. All that stuff about "95mb/sec" and "300x" and whatever, that's all hogwash, it's meaningless, and it causes the exact type of confusion that spawned this thread. So forget it all. Never even look at it.

The only thing you need to know at all is the "V" speed rating. That is the rating for the minimum continuous write speed that the card can sustain. There are three speed classes in use for modern camcorders: V30, V60, and V90. It doesn't matter what the numbers stand for, all you need to know is that your particular camera requires a particular "V" rating. For example, on the new CX350, you can record all its modes except the 400mbps mode, on a V30 card. Done. Get a V30 card, and everything will work, unless you need to use 400 mbps. If you do, then it requires a V60 card for that. And a V60 card will do everything that a V30 card will, so -- a V60 card is all you could ever possibly need for a CX350.

The "V" rating is everything. Nothing else matters. UHS-I, UHS-II, U(3), 300x, 95mb/sec, Class 10, all that is meaningless now. The ONLY thing that matters is that you have a "V" rating high enough for what your camera requires.
 
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