CF for HD video with 7D

[eduardo_barrento]

<p>Hi!<br>

I just get my 7D and I am completly new to HD video. My question is: what kind of CF card do you use? in terms of memmory (32gb?) and speed?<br>

Thanks<br>

Eduardo</p>

[frank_skomial]

<p>AVCHD modes require 24 MB/sec and 17 MB/sec, so appropriately fast memory is needed.<br>

16 GB is plenty for average, non long term shooting on any consumer grade HD camcorder.</p>

[borek_lupomesky]

<p>All I can say that my SanDisk Ultra II (nominally 15 MB/sec) has no problem recording video on my 5D Mark II (some ~34 Mbps bitrate). BTW, AVCHD is not 24 MB/sec but 24 Mbit/sec -- factor of 8.</p>

[PuppyDigs]

<blockquote>

<p>All I can say that my SanDisk Ultra II (nominally 15 MB/sec) has no problem recording video on my 5D Mark II (some ~34 Mbps bitrate). BTW, AVCHD is not 24 MB/sec but 24 Mbit/sec -- factor of 8.</p>

</blockquote>

<p>The 2010 SanDisk Ultra II is rated at 30 MB/sec, the same speed as last year's Extreme. I've used both the old and newer SanDisk Ultra II in my 7D and video was fine. My cards are only 8GB and they filled up really fast. I don't shoot much video but, if I did, I'd want a bag of 16 or 32GB cards.</p>

[KenPapai]

<p>I rarely shoot video with my 7D but when I do it's always with the <strong>SanDisk Extreme III CF </strong>card (30 MB/sec.) -- I use 8GB CF's. Never a lag issue (as far as I can tell). <br /> Thumbs up.</p>

<p>(I still find it hard to imagine, and wonder, at 8GB RAM in such a small package)</p>

[eduardo_barrento]

<p>Thank you all.</p>

[mark_james]

<p>Fast speeds are not needed for recording (the manual has the speed requirement, but I don't have it handy). I'm thinking that is is less than quoted above.<br>

However, getting 16 or 32 GB of data off of the card can be time consuming. A fast card may be helpful for that...</p>

 

[frank_skomial]

<p>Bit stream off the camera sensor scan speed is clearly defined for each video mode. Video speed is defined differently than memory write speed, where byte pieces are written from a camera. Some cameras, e.g. Nikon, allow parallel multiport writing of data to the memory. There is additional speed needed to accomodate serial bit stream to byte packing, addressing and writing bytes to the memory chip.</p>

<p>Therefore plain conclusion that bit rate divided by 8 to obtain byte rate, would not be apropriate.</p>

<p>E.g. for 24 Mbits per second, that one would think 24 /8 = 3 Mbytes per second of writing is needed, would end up with far too slow memory and choppy video. All depends on processing speed of a camera, but far greater speed is needed.</p>

<p>Using simple rule that bit rate of camera video mode would require memory of the same byte rate, is a safe bet.</p>

[steve_dunn2]

<p>The manual does indeed specify the minimum speed required for recording video, and it is indeed much less than suggested above: it's 8 MB/s. For vendors who use CD-style speed ratings, that's about 55x. The manual doesn't state what rate is required for different resolutions and frame rates, and I suspect this requirement is probably for 1080p30 and 720p60 (which would have roughly similar data rates). Logically, PAL and 24 frame rates should have slightly lower requirements, and SD should be lower still. But it's not as if 55x is high by today's standards; there are tons of inexpensive cards that are way faster than that, and as someone else pointed out, if you plan on shooting a lot of video, even though a faster-than-necessary card won't gain you anything in the camera, it will waste less of your time when you're downloading the resulting video files to your computer.</p>

 

<p>FWIW, I did a quick test when my 7D was new, using what were then my two fastest cards (80x and 50x). 1080p30 worked just fine with the 80x card; as suggested by the manual, the 50x card was not fast enough. I did not test any lower resolutions and/or frame rates.</p>

 

<p>As for card size, that's for you to determine based on what and how much you'll be shooting. The manual suggests approximate data rates of 330 MB/min for HD and 165 MB/min for SD. Each individual clip is limited to 29 minutes and 59 seconds or 4 GB, whichever comes first. You can do the arithmetic based on those numbers and your expectation of how much you'll be shooting between opportunities to download the videos to your computer or storage device.</p>