SD Cards - Where is the speed bottleneck? - AVS Forum
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post #1 of 21 Old 04-11-2012, 12:16 PM - Thread Starter
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Despite discussions indicating the critical nature of the card speed I find that for my high speed video applications so far all cards from class 2(or 4?) to 10 have worked. I'd like to better understand why and which video operations - recording or playback - might require the highest speed performance from the card. (I'm not primarily interested in which card to buy but what is going on.)

I use a Casio Ex FH100 camera. It records high speed video with much reduced resolution. The user's manual indicates that the Approximate Data Rate required for most high speed recording modes is 50 Megabits/second, the max rate listed in the table. HD video requires 30 Megabits/second. The manual indicates that an "Ultra High Speed Type SD memory card is recommended" and mentions that one reason is to avoid dropping frames when recording. I interpret "Ultra High Speed" to mean about a class 10. The camera will indicate when dropping frames during recording and I have never seen that in my high speed video applications. Playback would require less data rate since low resolution frames taken at 240 fps are played back at 30 fps. As one way to communicate videos I bought some cheap 2 Gb cards to loan. These cards seem to work.

Video compression might be important for data rate. ? My understanding of video compression is basically that the camera records one frame and then records the difference between that frame and each of the next X frames, for example, the next 30 frames (frame count varies for compression method and perhaps scene motion). Then the camera records another reference frame and repeats the process. If a camera were on a tripod it might produce more compressible video than if it were panning. I don't understand video compression that well.............but it seems that the required data rate could vary considerably based on the action in the video. ? Most of my videos are taken on a tripod or steady hand held without panning.

HD video with panning might be the most demanding for card speed? I have not played back HD on a TV from the camera.

Also, perhaps fragmentation of some sort slows the card after erasing data. I have not yet encountered problems as I erase data from the cards but I have not thoroughly tested the slower cards.

Anyway, the basic question is why do all cards seem to work for my application and what operation mode or situation requires the highest performance from the card?
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post #2 of 21 Old 04-11-2012, 05:34 PM
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Quote:
Originally Posted by Chas Tennis View Post

.......Anyway, the basic question is why do all cards seem to work for my application and what operation mode or situation requires the highest performance from the card?

It's about bits vs bytes. The math is a little weird because the important number is 1024! It's 5 PM here. I'm going to get a drink before I attempt this.

OK, I'm back. So, here goes.

There is a utility from Germany that operates in both German and English. It is called "H2testw". You will find it if you google it. It tests SD cards for errors and computes a writing and reading speed. I used it to test a Transcend 32 GB Class 10 SDHC card because I was confused about this speed stuff months ago. Besides, somebody posted that Transcend made inferior cards. I needed to know.

I learned (from Ungerman I think) that I was confusing Mbps and MBps. The highest my camcorder goes is about 28 Mbps when it is joyfully capturing the world in 1080pee60. That converts to about 3.5 MBps. The cards are rated in MBps.

So when I tested my card, the utility said it writes at 15.4 MBps. That means my cheap Transcend Class 10 card can record about about 4 times faster than the camcorder can put out. (They are currently selling for about $30.)

According to Wikipedia, a Class 10 does 10 MBps minimum. So my card, according to the utility, has a 50% bonus.

Since my camera at 28 Mbps only needs about 3.5 MBps (watch the "m"s and "M"s), a Class 4 card rated at 4 MBps would work. And, that's what the manual says I need, even though some of the experts here said anything less than the highest priced Class 10 would cause frames to drop.

If yours is doing 50, that's about twice what mine does. So, a Class 10 would be twice as fast as you need.

As near as I can tell, I've not dropped a single frame yet. You probably won't either.

Best....
Bill
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post #3 of 21 Old 04-12-2012, 08:24 AM - Thread Starter
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bsprague, thanks for the crystal clear explanation. It makes sense and seems to explain my experience with the SD cards. I wish I had seem this explanation in one of the many SD card discussions that I have read.

My cheap 2Gb cards work. They are not marked as to class and I have assumed that they are either Class 2 or 4. But many electronic products can be over spec. ? Class 2 should not work for 50 megabits/sec. A Class 4 should be slow for 50 megabits/sec. .......

Hold the presses...........

I just received another reply to my thread on dpreview. In addition it says that cameras use a buffer so that when I records short videos - which I always do for high speed videos of tennis strokes - there is a camera buffer that will record for a considerable time at high speed (higher than the card rating). Very interesting additional information and would explain why slow 2Gb cards are working fine in my high speed video application when producing short videos.

http://forums.dpreview.com/forums/re...ssage=41196068 Reply #3

If true this might explain fully my high speed video experience with the slow SD cards. It is too bad that there are so few people pursuing high speed video as this could be very useful information.
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post #4 of 21 Old 04-12-2012, 10:28 AM
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Quote:
Originally Posted by Chas Tennis View Post

....It is too bad that there are so few people pursuing high speed video as this could be very useful information.

Not true! Everyone with one of the many current video cameras that shoots in 1080p60 can do it. I looked up your camera and it does 40 frames per second.

I discovered this by accident. By brother built a working replica of 1776 British rifle. I took a clip of him shooting it. About the same time I learned that the software that came with the camera will turn each frame into reasonable .jpg photo.

My brother asked if I could tell how long it took between trigger pull and the bullet coming out the barrel from the video. I used the free camera software and found out it took 7 frames by saving each frame to a .jpg. My brother was happy to learn it took 7/60ths of a second!

Also at the same time I was learning how to use an Adobe video editor and was experimenting with mixing .jpg photos with video clips.

My light bulb lit when I cut the video clip a couple of frames before trigger pull and inserted the 7 .jpg photos. I set each to display for about 1/2 second. The result is that I turned about a 1/10th second into 3 seconds.

You can see my results at https://vimeo.com/36973087 Look for it at 2:05 into the 3:20 video.

Since then I've learned I can do it automatically. The editing software has a "time stretch" tool! I cut the clip down to the frames including the gun fire, grabbed the end of the clip and stretched it a bunch. You can look at it here: https://vimeo.com/40244658 (when Vimeo is done processing it which is estimated to be in 30 minutes of this posting!)

So everyone with a 1080p60 capable camera can pursue high speed video!

Bill
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post #5 of 21 Old 04-13-2012, 02:35 PM - Thread Starter
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Quote:
Originally Posted by bsprague View Post

Not true! Everyone with one of the many current video cameras that shoots in 1080p60 can do it. I looked up your camera and it does 40 frames per second.
............................................................ ................................
My brother asked if I could tell how long it took between trigger pull and the bullet coming out the barrel from the video. I used the free camera software and found out it took 7 frames by saving each frame to a .jpg. My brother was happy to learn it took 7/60ths of a second!
............................................................ .............................
My light bulb lit when I cut the video clip a couple of frames before trigger pull and inserted the 7 .jpg photos. I set each to display for about 1/2 second. The result is that I turned about a 1/10th second into 3 seconds.
............................................................ ...................................
So everyone with a 1080p60 capable camera can pursue high speed video!

Bill

Not so fast!

Cameras that do 60p are pretty fast especially for slower athletic movements. However, no matter how you process the video afterward and change the display time you only have the real information sampled at 60 fr/sec. It all works well if things progress in an orderly way from A to B - somebody swinging a baseball bat might work - but if there are very fast motions or events 60p can miss or distort what has happened.

The Casio FH100 does 120, 240, 420 and 1,000 fr/sec with lower spatial resolution the higher the frame rate. It does 40 frames per second burst mode recording 30 high resolution still images, 9 MB. However, the Jello Effect distortions are much larger than in the low resolution HSV images. Also, the FH100 has full MANUAL control of the shutter speed and can easily produce bright video in direct sunlight using its fastest shutter speed of 1/40,000sec.

The event that you shot was surprisingly slow for gun shots because the delay between the trigger and muzzle flash was over one tenth of a second.
Therefore the 60p framing captured 7 frames.

Your videos are excellent for displaying what is going on in a very brief time so that people can view it and understand it. Likewise, the applications that add frames between the ones that were originally taken can display fast things slowly for proper viewing. However, the added frames for those applications are fabrications. If you analyze high speed events such a a tennis serve with such videos you cannot see what is really happening. You will draw false conclusions.

"So everyone with a 1080p60 capable camera can pursue high speed video!" Not possible.

Casio came out with high performance high speed video cameras first in 2008 with the F1. Next came the FH20, FH25 and last the FH100 in 2010 - the last because people did not buy enough. These cameras had MANUAL shutter control in high speed video and could reduce motion blur. At the same time Casio and others made cheaper high speed video cameras with the same high frame rates to 1,000fps but the cheaper cameras all had AUTO shutter control. With AUTO control they could not minimize motion blur.

My Casio FH100 camera costs $239 in 2010 while the cheaper HSV cameras would sell for around $100. Buyers just did not understand and appreciate high speed video features such as full manual shutter speed control. Check the price for a used Casio FH100 now, about twice the original new cost. Nobody now makes a high performance affordable high speed video camera with MANUAL shutter speed control.

High Speed Video
http://www.kinovea.org/en/forum/viewtopic.php?id=435

Jello Effect Tests Casio FH100
http://forums.dpreview.com/forums/re...ssage=39168709
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post #6 of 21 Old 04-13-2012, 05:21 PM
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Quote:
Originally Posted by Chas Tennis View Post

Not so fast!

Thank you for the clear explanation. Can I call it "moderate speed"?

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post #7 of 21 Old 04-14-2012, 07:32 AM - Thread Starter
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Quote:
Originally Posted by bsprague View Post

Thank you for the clear explanation. Can I call it "moderate speed"?

Bill

You are recording at 60 fr/sec and processing to stretch the time period of interest to make it longer for great viewing, probably at 30 f/sec. In the second video I believe that you stretched the trigger-to-muzzle-flash time from 0.12 sec to 3.5 sec, 29X. I would think over the wording and explain the overall process to minimize misunderstandings by the viewers. You'll come up with additional creative ideas as you think about it.

The great majority of people just want to view a video and don't care about analysis and accuracy.

Frequently people will comment in high speed video threads that there are applications that can stretch the display time by creating frames, but these as mentioned are fabricated frames, false frames. The difference between producing an attractive and viewable video with 30 f/sec display and having something that accurately represents what happened, usually seen by stop action frame-by-frame analysis, becomes confused to most readers. Unfortunately, the more serious efforts to produce high performance HSV equipment - a few of Casio's camera as mentioned - aren't appreciated and disappear as with the wizard gadget Casio cameras.

Someday I would like to upgrade my low resolution high speed video to HD HSV. That's a difficult engineering problem in an affordable camera.

You have an interest and would enjoy high speed video.

Your videos look very sharp with low motion blur. I guess that the shutter speed was fast. You might also post on YT to broaden the audience.
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post #8 of 21 Old 04-14-2012, 03:28 PM
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...... "In the second video I believe that you stretched the trigger-to-muzzle-flash time from 0.12 sec to 3.5 sec, 29X. "
-I didn't calculate it. I have been trying to learn video editing. One lesson included a demonstration of stretching or shrinking a clip in the time line. I thought the gun shot would be a fun experiment. I stretched it far beyond what seemed resonable. To my surprise, the software made something watchable.

......."You'll come up with additional creative ideas as you think about it. "
-It's nice you have that much confidence in me! (grin)

......."The difference between producing an attractive and viewable video with 30 f/sec display and having something that accurately represents what happened, usually seen by stop action frame-by-frame analysis, becomes confused to most readers.
- In trying to learn video I read a book that said the first rule is that it better be fun to watch, or your viewer will quickly find something else.

........"Unfortunately, the more serious efforts to produce high performance HSV equipment .......aren't appreciated and disappear as with the wizard gadget Casio cameras."
-It has not been long that cameras could be good at both video and photos. Single purpose consumer cameras are gone. Instead manufacturers stuff a lot of features in various models. Perhaps a camera will come along that includes better HSV as one of those features. One can hope.

...."Your videos look very sharp with low motion blur. I guess that the shutter speed was fast."
-I can't tell you what the shutter speed was. I tend to use "intelligent auto" a lot so I can concentrate on content.

.....You might also post on YT to broaden the audience.
-I do have some stuff on YT. I'm not looking for a broad audience. Instead, I'm looking for an delivery channel that does not distract. YT screens are busy. Videos often end with encouragement to watch similar subjects from other photographers. Maybe I should have my own website with links to rented storage space "in the cloud" somewhere.

Bill
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post #9 of 21 Old 10-13-2012, 03:38 PM - Thread Starter
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1st failure of 2GB SD card to record high speed video -

The original Post #1 was for better understanding of the speed requirements of SD cards. One point was that my slow SD cards had all so far worked for high speed video recording requiring 50 Mb/sec. I had used 4-6 slower SD cards with no failures.

I just had my first recording failure using a 2 GB SD card. My application was to record tennis serves for a few minutes using a Casio FH100 at 240 fps (reduced resolution). The manual says that 240 fps requires 50Mb/sec data rate.

The recording worked OK for a few minutes and then skipped some frames near the end. I believe that it also skipped frames recording at 120 fps that also requires 50Mb/sec data rate.

See also Post #3 discussing the possible effects of the camera's buffer.

I believe that the degree of video compression that affects video file size may also affect SD card performance, but have no information on the effect of video compression.
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post #10 of 21 Old 10-13-2012, 07:21 PM
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Chas,

Go back to post #2, Maybe the utility "H2testw" will find a flaw in the SD card you are using.

Bill
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post #11 of 21 Old 10-14-2012, 06:08 AM
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I don't understand why people use antique 2GB SD cards today when a SanDisk 32GB SDHC Ultra Class 10 30MB/s UHS-I card sells for under $20.
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post #12 of 21 Old 10-14-2012, 08:46 AM - Thread Starter
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Originally Posted by jogiba View Post

I don't understand why people use antique 2GB SD cards today when a SanDisk 32GB SDHC Ultra Class 10 30MB/s UHS-I card sells for under $20.

The typical forum discussion basically says to buy a high class card and don't waste your time worrying about it. For the average use, I agree.

Communicating Videos. I see a use for cheap cards to send or hand videos to other people. In my case, suppose that I want to give a high speed video to someone of their tennis strokes. The free internet options are very limited for file sizes of 2GB. With one of the $5 or under cards they could take home a copy of their tennis strokes and view it stop action, frame-by-frame. They could also return the cards - loaner cards. I could see that instructors of golf, tennis, dance, etc might be interested but then the cards really would have to be reliable.

Three brands of 2GB or 4GB cards that I have used have not shown any skipped frames or otherwise failed - with my limited testing. One card failed. Since I am using the cards out of spec in a limited application, I'll leave out the brand names. My application is limited to short, low resolution, high speed video taken from a tripod. Complicating the matter is the influence of compression which I do not understand. I shoot on a tripod and that makes video compression work better.

The OP was to better understand the card speed limitations and perhaps have some replies that identified the bottlenecks, such as, 'long HD video playback (not computer limited) is very demanding for card speed'.
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post #13 of 21 Old 10-14-2012, 09:08 AM - Thread Starter
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Quote:
Originally Posted by bsprague View Post

Chas,
Go back to post #2, Maybe the utility "H2testw" will find a flaw in the SD card you are using.
Bill

That is an excellent suggestion.

I find inconsistency between what I have read on forums about SD cards and my limited testing. Mostly, I'd like to understand it. I had hoped for some specific bottlenecks or modes of camera operation that the cards can't handle.

Based on my camera tests of specific operation modes, I'd feel comfortable buying some brands of 2GB & 4 GB SD cards.
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post #14 of 21 Old 10-14-2012, 09:10 AM - Thread Starter
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Bill, BTW, does that FZ150 of yours in high speed video mode have a Shutter Priority semi-auto mode?
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post #15 of 21 Old 10-14-2012, 08:06 PM
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Quote:
Originally Posted by Chas Tennis View Post

Bill, BTW, does that FZ150 of yours in high speed video mode have a Shutter Priority semi-auto mode?
Actually, it is not mine. I bought if for my wife. She doesn't let me touch it. So, I don't know!

The book says:
"[HIGH SPEED VIDEO]
This will record 220 frames/second, recording very fast movement that cannot be seen
with the naked eye as a motion picture.
1 Press the motion picture button to start the recording.
• Release the motion picture button right after you press it.
2 Press the motion picture button again to stop the recording.
Note
• It cannot be recorded into the built-in memory.
• Motion pictures will be recorded in the Motion JPEG format. Use the “QuickTime” or
“PHOTOfunSTUDIO” software on the CD-ROM (supplied) to play back motion pictures on a
computer.
• Audio is not recorded.
• Motion picture can be recorded continuously for up to 2 GB.
• The focus, zoom, exposure and White Balance is fixed to the value at the beginning of the
recording motion picture.
• Under fluorescent lighting, flicker or horizontal bars may be seen."

Bill
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post #16 of 21 Old 10-25-2012, 02:27 PM
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Originally Posted by bsprague View Post


It's about bits vs bytes. The math is a little weird because the important number is 1024! It's 5 PM here. I'm going to get a drink before I attempt this.


OK, I'm back. So, here goes.


Best....

Bill

Wow, great info Bill. I've been researching this since I will be buying a Sony HDR CX760 soon and I need extra storage for a trip. I am pretty detail oriented and I never noticed the Mbps vs. MBps designations. I had been researching whether I needed to buy the SanDisk Ultra 32GB at $24 or go for the Extreme at $42 (Costco sale price). From what you are saying, the Ultra will be more than enough. Is there any advantage for me to get the Extreme? The added cost isn't a factor, but I don't want to pay extra for nothing!
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post #17 of 21 Old 10-25-2012, 08:05 PM
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Originally Posted by knowspinzone View Post

Wow, great info Bill. I've been researching this since I will be buying a Sony HDR CX760 soon and I need extra storage for a trip. I am pretty detail oriented and I never noticed the Mbps vs. MBps designations. I had been researching whether I needed to buy the SanDisk Ultra 32GB at $24 or go for the Extreme at $42 (Costco sale price). From what you are saying, the Ultra will be more than enough. Is there any advantage for me to get the Extreme? The added cost isn't a factor, but I don't want to pay extra for nothing!
As near as I can tell, there is no advantage in the camera. It may be, depending on your computer, that file transfer could be faster when you put the SD card in it. The appropriate guide is the camera manual. The cheaper card should be fine.

BTW, it was a guy who posts here named Ungerman that taught it to me.

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post #18 of 21 Old 10-26-2012, 05:06 AM
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Thanks Bill. Now one more question for anyone. I will be taking the camcorder from the USA to Europe. If I need more memory can I buy SDHC memory cards in Europe? I am not sure if there is any difference be between memory cards due to the two different systems - NTSC and PAL.
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Originally Posted by knowspinzone View Post

Thanks Bill. Now one more question for anyone. I will be taking the camcorder from the USA to Europe. If I need more memory can I buy SDHC memory cards in Europe? I am not sure if there is any difference be between memory cards due to the two different systems - NTSC and PAL.
You can buy SD cards everywhere and there is no difference. They all need to be formated and be sure you do it in your camcorder to create the right file structure.

Class 10 32GB cards have become pretty cheap. They take up no luggage space. If you can afford to go to Europe and one of these camcorders, you can afford to take a few with you in a nice protective case.

As a tourist I typically shoot lots of 10 to 20 second clips for later editing. I don't even fill one 32GB clip in week's travel if I delete the crappy clips as I go. But, I think you can find three or four SD cards in my luggage.

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post #20 of 21 Old 10-26-2012, 04:57 PM
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I suspected there was no difference, but I appreciate your confirming that for me.

I had toyed with the idea of bringing a pocket hard drive like a Western Digital 500GB, but I think like you say, I can just delete the crappy clips. I have lots of those!
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post #21 of 21 Old 10-26-2012, 08:23 PM
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Quote:
Originally Posted by knowspinzone View Post

I suspected there was no difference, but I appreciate your confirming that for me.
I had toyed with the idea of bringing a pocket hard drive like a Western Digital 500GB, but I think like you say, I can just delete the crappy clips. I have lots of those!

There are various strategies for ensuring photo and video data loss can be minimized.

One is to use a lot of smaller cards. For example, you put in a fresh card each morning and afternoon for a weeks trip. You go home with 14 cards. If one is bad, you loss is minimal.

Another is to use SD card readers that have storage in them, like this: http://www.amazon.com/PicPac-Memory-Reader-Storage-7625/dp/B003QP49N0/ref=sr_1_1?ie=UTF8&qid=1351307817&sr=8-1&keywords=sd+card+backup+device

A third is to take the smallest computer you can find that will read cards and copy each day's new shots to the HDD.
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