Understanding CF cards for HD video?

[Art Varga]

Question - I know the speed of the card impacts the time it takes to upload but does it matter for recording video as long as your not experiencing buffer issues? I've been using SanDisk Ultra ll 15MB/S with no issues. They're relatively inexpensive so I'm wondering if there is any reason to buy faster cards. I think the minimum requirement for the 5D is 9MB/S.

[Jon Fairhurst]

I would personally stick with UDMA cards. As Barry Green wrote, Tim Smith of Canon stated that there have been problems with non-UDMA cards.

I've read that with slow cards, video still records, but the encoder's bitrate might adjust downward for slower cards. Sure, you'll still have video, and it might look fine, but you never know if the compression would be better on a faster card.

UDMA is cheap insurance.

[Shaun Walker]

I hope I find out that UDMA cards are pricey excess in real life 7D video usage, 'cause the next level down is so much more affordable if you have to load up with big fast cards for a big, long field trip ... but you might be right, we'll see.

As a frequent still shooter, I will make sure my main/primary cards are tough and UDMA, regardless, though.

[Kin Lau]

Originally Posted by Jon Fairhurst

I've read that with slow cards, video still records, but the encoder's bitrate might adjust downward for slower cards. Sure, you'll still have video, and it might look fine, but you never know if the compression would be better on a faster card.

UDMA is cheap insurance.

I can confirm that this is not true. I've been testing this with my 7D.

With a slower non-UDMA card, the buffer fills - you see a status bar on-screen, and then it simply _stops_ recording when the buffer is full.

Bitrates are running btwn 45-47mbit/s, or 5.75MB/s.

[Jon Fairhurst]

Originally Posted by Kin Lau

...With a slower non-UDMA card, the buffer fills - you see a status bar on-screen, and then it simply _stops_ recording when the buffer is full...

Well, at least you know when your card isn't fast enough.

I wonder if they changed their approach in the 7D. I've never heard of this behavior in the 5D2.

[Brian Boyko]

I can tell you for sure that 4GB 150x cards don't cut it. (got my 7D today) Cuts out after 5 seconds or so of recording.

Going to return the cards I bought and wait until someone comes out with a good, cheap card recommendation that's KNOWN to work with the 7D.

[Jon Fairhurst]

I'm not 100% sure, but I believe that UDMA is the key requirement.

Canon recommends UDMA cards for the 5D2, but non-UDMA cards don't fail hard. (They apparently show artifacts like streaking and might drop frames.)

It seems that the 7D doesn't fail gracefully with non-UDMA cards. A better solution would be to fail gracefully, but to notify users that the card is too slow for optimum use.

[Chris Hurd]

Originally Posted by Shaun Walker

... someone was saying that his Extreme III or equivalent was great except for when taking a still during HD video recording -- that it would cause a bit more of a delay and a few occasional lost frames ...

That's not a function of the card at all. When taking a still photo during video recording, there will be a 1-sec. freeze frame recorded to video. That's just the way the camera works. Card choice does not affect this.

Originally Posted by Chris Barcellos

...I am not so sure we can trust his technical pronouncements.

I have known him personally for ten years, so believe me, *I* am sure we can trust his technical pronouncements.

Originally Posted by Jon Fairhurst

I'm not 100% sure, but I believe that UDMA is the key requirement.

Canon USA made this clear to me in November of last year when I was originally briefed on the 5D Mk. II. Perhaps it is my own fault for not clearly emphasizing this enough in our 5D Mk. II forum, but UDMA has *always* been the key requirement in selecting Compact Flash cards for the EOS 5D Mk. II (and now the EOS 7D). Hope this helps,

[Chris Hurd]

Picked up this SanDisk 8GB UDMA 400x 60MB/s Compact Flash card yesterday ($120)... I'll let y'all know how it goes.

[Kin Lau]

Just to add that I've use my 7D with several non-UDMA A-Data 16gig and 32gig CF's (A-Data has a UDMA and a regular line, these are the regular type), and they work fine in video mode. They're about 1/2 the speed of my Extreme III's 30MB/s CFs when shooting stills. I also have a 4gig A-Data CF, and that one stops recording in about 5 seconds.

In using non-UDMA cards, I've not notice _any_ streaking or artifacts or drop-frames. 5.75MB/s or 47mbit/s (same bitrate for 720/60p, 1080/24p and 1080/30p) is not very much at all.

[Don Miller]

Originally Posted by Jon Fairhurst

Well, at least you know when your card isn't fast enough.

Actually Canon suggests that the processor may cut the data rate on cards sensed as slower. The speaker even suggested that slow cards may cause higher noise.

I'm in the "it's not worth the risk" camp.

I'm not understanding about UDMA cards as being "pricey". What are you guys doing, using cards only once?

[Jon Fairhurst]

Originally Posted by Don Miller

Actually Canon suggests that the processor may cut the data rate on cards sensed as slower. The speaker even suggested that slow cards may cause higher noise.

That was for the 5D2, wasn't it? The 7D could be different.

[Don Miller]

Originally Posted by Jon Fairhurst

That was for the 5D2, wasn't it? The 7D could be different.

Unless Canon is definite the logical approach is conservative. It's an odd area to go cheap. I'm not even suggesting the best cards are necessary. Just the UDMA cards from the brands that have consistently produced trouble-free memory.
Now if a card has worked well for several hours of shooting and the footage has been edited, that's a pretty good test. But early on I had some 300X cards that showed some buffer filling but didn't quit for a few tapings. But finally I did get a buffer overflow that stopped the recording. There are infrequent but not unexpected conditions in the data flow that are difficult for non-UDMA cards to handle

[Kin Lau]

You have to remember that UDMA CF's are designed more for DSLR's with their "bursty" style of files writes rather than the constant but much lower speed writes of video.

The UDMA spec is old, that's the old ATA/ATAPI standard. Most of us have moved on to SATA drives now. The UDMA spec is only for the _max_ transfer speed of the _interface_, not the actual thru-put of the card. So it's not surprising that Don is running into this problem with his 300x cards. Do you mind letting us know which brand/model they are?

The manual for my Edirol R09 actually recommends not using the fastest SDHC cards available, but sticking with Class 4 instead, citing the "bursty" nature of the faster cards as a reason.

It would be nice if DVInfo could keep a database similar to the Rob Galbraith SD/CF page of which SDHC and CF cards have worked well for video, and which cameras they were tested on.

[Stephen Mick]

Just an FYI…

I set my 7D up in the backyard, wide lens, lots of detail, and let it record an 11 minute clip to one of my SanDisk Extreme III 32GB cards. No problems at all, no buffer issues, it just works.

--SM