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PostPosted: Thu Jan 27, 2011 1:59 am 

Joined: Mon Jan 24, 2011 10:22 pm
Posts: 13
I finally got my 4 Sony eye camera setup capturing video with iPi Recorder. My system (maybe the USB 2.0) doesn't seem to have the bandwith to capture all four cameras at 640x480 60 fps. I can lower it to 320x240 60 fps or 640x480 40 fps and it captures fine.

My question is, what is more important, frame rate or resolution?

One more question... When I record at 640x480 RAW mode, it appears to still be capturing at 320x240 when I view the playback in windows media player. Each video is split into 4 grayscale images that are stacked up, but each image is 320x240 instead of the expected 640x480. Is that expected? Is it actually only 320x240 even when setting it to 640x480?


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PostPosted: Thu Jan 27, 2011 9:56 am 

Joined: Mon Aug 03, 2009 1:34 pm
Posts: 2336
Location: Los Angeles
Gillissie wrote:
My question is, what is more important, frame rate or resolution?

It depends. In general, I'd say go for higher framerate, especially for faster motions. Higher framerate reduces motion blur which allows for more precise tracking. Higher resolution, on the other hand, gives you more detail, so it's probably better for slow, subtle movements.

As for RAW Bayer format movies, in a standard video player I typically see what appears to be a matrix of 16 'half-size' images, which I think is normal. iPi DMC's player assembles this data into 640 x 480 res whole frame. Are you seeing something else?

Greenlaw

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PostPosted: Thu Jan 27, 2011 1:23 pm 

Joined: Mon Jan 24, 2011 10:22 pm
Posts: 13
I see the same thing, but question how a half-sized image can be assembled into an image twice its size without interpolation. But if that's the way it works best, I'll give it a shot.

I have a shopping cart with a USB 3.0 card, hub, and active extension cables in the hopes that I can capture 4 camera's at 640x480 60 fps. I am capturing to a SATA drive with 80 MB/s write speed, so I know the bottleneck isn't the drive. The bottleneck happens when the original data throughput reaches 50 MB/s, which makes sense since USB 2.0 has a bandwidth of 40-50 MB/s. Any last minute advice on this before I click to buy?


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PostPosted: Thu Jan 27, 2011 1:44 pm 
iPi Soft

Joined: Wed Apr 07, 2010 4:33 am
Posts: 370
Gillissie wrote:
I see the same thing, but question how a half-sized image can be assembled into an image twice its size without interpolation. But if that's the way it works best, I'll give it a shot.


Most of modern digital cams uses bayer patter for color recording. For more information you can take a look at http://en.wikipedia.org/wiki/Bayer_filter.

Gillissie wrote:
I have a shopping cart with a USB 3.0 card, hub, and active extension cables in the hopes that I can capture 4 camera's at 640x480 60 fps. I am capturing to a SATA drive with 80 MB/s write speed, so I know the bottleneck isn't the drive. The bottleneck happens when the original data throughput reaches 50 MB/s, which makes sense since USB 2.0 has a bandwidth of 40-50 MB/s. Any last minute advice on this before I click to buy?


Have you read this article http://ipisoft.com/en/wiki/index.php?title=USB_controllers? It can help.


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PostPosted: Thu Jan 27, 2011 2:19 pm 

Joined: Fri Sep 24, 2010 12:37 pm
Posts: 104
You don't say much about the rest of the system but don't be so sure that the drive isn't an issue despite what it says on paper.

This is my recipe for 6 cameras at 640 x 480 @ 60fps

viewtopic.php?f=2&t=4830


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PostPosted: Thu Jan 27, 2011 8:17 pm 

Joined: Mon Aug 03, 2009 1:34 pm
Posts: 2336
Location: Los Angeles
Yes, the speed of the drive can make a big difference in video capture bandwidth but be wary of listed drive specs. In real world usage, the actual performance is rarely what the manufacturer claims it is.

Some tips: don't record to your system drive; you will want to record to a second drive. I was able to capture video at full res and speed for four cameras using a 7200 rpm SATA2 drive. I also made sure there was no more than 2 camera per USB controller. (Make sure you read the iPi Wiki article referenced by Andrew.)

As djtaylor discovered, moving up to a decent SSD may allow you to do the same with six cameras.

BTW, what type of computer do you have? You'll want at least a quad-core system to capture from four cameras at full res and speed.

G.

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PostPosted: Thu Jan 27, 2011 9:11 pm 

Joined: Mon Jan 24, 2011 10:22 pm
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djtaylor wrote:
You don't say much about the rest of the system but don't be so sure that the drive isn't an issue despite what it says on paper.

This is my recipe for 6 cameras at 640 x 480 @ 60fps

viewtopic.php?f=2&t=4830


The performance I mentioned is not based on paper, it's based on actual performance testing using "Bart's Stuff Test". I just ran it again to verify, and it's actually writing at 100 MB/s.

I'll check out your recipe...

[edit] The SSD sounds like a good idea, but I'll see how my SATA drive fares first. It is this drive: http://us.toshiba.com/accessory/PH3100U-1EXB


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PostPosted: Fri Jan 28, 2011 5:30 pm 

Joined: Fri Sep 24, 2010 12:37 pm
Posts: 104
Just for consistency, i've just tried the same test as you and my SATA drive writes at 86MB/s and choked almost instantly with 6 cameras with IO errors. What sort of problem are you seeing, packets dropped in the recording software or IO errors?

Amusingly, Bart's Stuff Test reports 68MB/s on my SSD that eats 6 camera's data streams for breakfast, lunch and dinner. :)


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PostPosted: Fri Jan 28, 2011 6:02 pm 

Joined: Mon Aug 03, 2009 1:34 pm
Posts: 2336
Location: Los Angeles
I got similar results. Techically, my SATA should be able to handle it but it can't. The SSD on the other hand, has no problem. I'm guessing that even though they both can handle high transfer rates, the SSD's ability to sustain the highest rate for the duration of an iPi Recorder recording (in my case, it can sometimes be several minutes long,) is just better.

Greenlaw

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PostPosted: Thu Feb 03, 2011 10:51 pm 

Joined: Mon Jan 24, 2011 10:22 pm
Posts: 13
Definitely good to know. After I get my USB 3.0 stuff in the mail and test it with my SATA drive, I might have to make a trip to Best Buy for a SSD.


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