dropped frames while shooting at 50fps - why?

[memostothefuture]

hello,


I use the sandisk extreme III 8GB compact flash card (30mb/s) on a 7D. I thought this setup should be able to record the 1280x720 50fps video without dropped frames but I still have this issue when the action in frame gets too busy.





any thoughts on what my error might be?

[neuroanatomist]

Welcome to the TDP Forums!

I use the sandisk extreme III 8GB compact flash card (30mb/s) on a 7D

I think that instead of the Extreme III, you'll want to get a faster card with UDMA, such as the Extreme 60 MB/s UDMA (I use those in my 7D).


If you check out Sandisk's recommended cards for the 7D, you'll see only the Extreme 60 MB/s UDMA and Extreme Pro 90 MB/s UDMA cards on the list. UDMA cards provide faster burst capabilities for still shooting, and Canon recommends a UDMA card if you are taking still photos while capturing movies.
<div>Hope that helps...</div>


--John

[memostothefuture]

hi john,


yeah, that was a typo on my part. already corrected it: I used a sandisk extreme III 30mb/s card (8GB). I don't see any UDMA label printed onto it. I wonder if this card should be technically able to capture the 50 fps footage, in which case I would look at the file again on a different computer using different software, or if this can be chalked off to the 50 fps mode just not being feasible with this card.


(I thought I had purchased the second fastest card sandisk makes, which is why I am so confused.)





thanks for your help!

[neuroanatomist]

I thought I had purchased the second fastest card sandisk makes, which is why I am so confused

The Extreme III is a 30 MB/s non-UDMA, the Extreme IV is 45 MB/s UDMA, Extreme (with no Roman numerals) is 60 MB/s UDMA, and the Extreme Pro is 90 MB/s UDMA.


In general, the faster the card, the less likely to drop frames.


Whether you purchased the second fastest card Sandisk makes depends on when you bought the card. For example, the Extreme Pro was released right around the time that the 7D came out (Sept, 2009). The Extreme IV came out one year earlier, so the Extreme III was the second fastest card prior to Sept, 2008. But it seems that after releasing the Extreme IV, Sandisk changed their naming scheme, dropping the Roman numerals and simply going with Extreme (60 MB/s) and Extreme Pro (90 MB/s).

[memostothefuture]

hm. I searched a bit around and read this:


"The<span class="hl0"]7Dtransfer video (both) 1080 and 720p at approx. 330 MBytes/minute. This corresponds to around 5.5<span class="hl3"]MB/sec. You will be fine with either 30 or 60 MB/s cards"


so even if this card reads at 'just' 30 mb/s I should still be fine, right? or is the assumption above (5.5mb/sec of data being written in this mode) incorrect?


I'm confused, sorry.

[Daniel Browning]

Well, the 'read' speed of the card doesn't really matter -- just write. And even then, the method that manufacturers use to rate their card write speed is not very realistic. It's like car manufacturers rating an MPG like this: "50 MPG (when going downhill, with no passengers, nitroglycerin fuel, and gale-force winds at your back. Your mileage may vary.)" The speed in real life situations is usually less.


That said, 5.5 MB/s is not a very high write speed, and even low end cards should be able to keep up. Furthermore, it should only happen when the card buffer warning icon starts to fill up on the LCD -- if you didn't see that then it probably wasn't the card's fault. If there really are dropped frames in the video file, I think the most likely cause is a software bug.

[neuroanatomist]

You should be fine. Canon recommends using at least 8 MB/s cards. But, as Daniel stated, what a manufacturer states as a speed and what the speed is in practice depend on the card and your camera. Rob Galbraith has tested many card types in several cameras. Unfortunately, the 7D is not one of the cameras he tested. But, to apply some of his numbers, your Sandisk Extreme III 30 MB/s card tests out with an actual write speed of 18.4 MB/s on a 50D, but only 7.5 MB/s on a 1DIII.


So, it could still be the card, or the camera itself, or the software you're using. Perhaps try a different viewer ( Canon's ZoomBrowser, for example, or some other free software). If the problem persists, perhaps getting a new card is the answer. Also, make sure you're running the latest firmware (1.2.2).

[memostothefuture]

thanks for your help everyone.


in the meantime I've checked one video on a different machine (a mac pro with massive loads of RAM) and there weren't any dropped frames, so that seems to have been a playback issue with my quicktime player. my firmware btw is up to date. the other video I tested did have dropped frames at the very beginning (about two to three seconds in). I'm beginning to suspect I caused that by touching dials on the camera. I will do another test tonight and if I can't identify the problem myself I'll upload the file to my server. perhaps you'll spot my mistake.