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Requirements for DPX capture

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Gary Askham
Requirements for DPX capture
on Sep 4, 2012 at 12:20:20 pm

Does anyone know the system requirements to capture a 1920x1080 24fps DPX sequence within Resolve (or Media Express)

I currently run a 2.93GHz Quad Core Nehalem Mac Pro with a couple of Nvidia Quadro 4000 gfx cards and the Blackmagic Decklink HD Extreme 3D+.

The storage is 4 drive Serial Attached SCSI Sonnet RAID Drive capable of an average 140MB/s.

At the moment I can capture ProRes 4444 happily and even uncompressed HD 10 bit YUV. But when I try to capture a DPX stream it drops frames after about 10 seconds.

Is the bottleneck the storage, the processor... or something else?

------------------------
FCP and Avid Technical Support
Air Post Production
Shoreditch - London


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Sascha Haber
Re: Requirements for DPX capture
on Sep 4, 2012 at 1:24:57 pm

Sure, you need 250 mb/s for DPX
I am running 4 internal WD FASS and I have 550 mb/S available.

A slice of color...

DaVinci 9b3 OSX 10.8
MacPro 5.1 2x2,4 24GB
RAID0 8TB
GTX 470 / Quadro 4000
Extreme 3D+

Colorist / Aerial footage nerd
http://vimeo.com/saschahaber


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Arno Beekman
Re: Requirements for DPX capture
on Sep 4, 2012 at 1:30:04 pm

not knowing what kind of DPX you're trying to create here's a little math:

1920 x 1080 pixels, each have 3 colour values stored in 10 bit at 24 fps:

1920 * 1080 * 3 * 10 * 24 = 1492992000 bit/sec
1492992000 / 8*1024^2 = 177,978515625 MegaByte/sec ≈ 178 MB/s
that more than your RAID can handle isn't it?

that doesn't mean that that is the problem though. the bottleneck might be earlier in the chain...


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Joseph Owens
Re: Requirements for DPX capture
on Sep 4, 2012 at 2:40:31 pm

[Arno Beekman] "
that doesn't mean that that is the problem though. the bottleneck might be earlier in the chain..."


Yes, that bitrate is simply for file transfer, and doesn't take sampling and encoding into account. Hardware capture in ProRes is fairly straightforward since the bitrate is only about 10% of Uncompressed, and you are only creating one file. DPX capture, depending on the bit depth, requires more processing and disk access becomes even more critical since you are writing one file per frame, which can quickly overflow any caching, so then the capture chokes.

The usual minimum number I work with in 1080P is 185 MB/sec, but with an external 20-drive quad-lane fiber channel RAID that is capable of 1.2GB/sec sustained. Seems like overkill, but that's still cutting it close to the minimum for 4K.... uncompressed flows.

Its just the math.

jPo

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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