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DV capture (Read 3271 times)
Citizen_Kang
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DV capture
Sep 20th, 2001 at 11:33pm
 
Hey Rad,

In a couple of spots in the guides (ex. Behemoth) you have   "DV only requires 3.6MB/s" - Now I have very little practical experience with DV (capturing or editing) but:

1) shouldn't it be 36MBps:

  Resolution of 1024 x 768, YUV (16bpp), 24fps ->

  [1024x768x16x24] / [8x1024x1024 -> to convert to MBps]
  = 36MBps

( if it were 3.6MBps, using 1394 would be a bit of overkill, USBv1.0 would be all one would ever need, and for that matter, the PCI bus would probably suffice too instead of isolating to SCSI ) 

2)  Rather than a set figure, isn't it instead the case that the minimum data transfer rate that DV requires is foremost dependent upon the resolution that your capturing at!  ie. if a camcorder had a max res. of 800x600 then (assuming the same image format and frame rate as above) one would only require a bus that can sustain a ~22MBps (which, agian, would be best served by a firewire connection to the PC)

Cheers, CK
 
 
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Rad
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Re: DV capture
Reply #1 - Sep 21st, 2001 at 3:31am
 
Kang,

If you look here:

http://www.videoguys.com/storage.htm

.. storage rule #4, you'll see they say:

"DV is a fixed 3.5 megs per second."

Actullay, I've heard the number 3.6 used more (than 3.5), but it doesn't really matter. The 3.5/3.6 number is used many times all over the Net.

My own calcs also come to the same conclusion.

You use 1024x768. Our DV = 720x480 .. maybe that's where your calcs go awry.

Firewire is used not only for data x-fer, but also for device control. I think things would be more responsive is they used separate busses for each.

Firewire actually just *transfers* the (already captured) video to the hard drive. In the case of DV, the word "capture" is actually a misnomer. It's really just *transferred*.

Diff resolutions like you talk about deals with analog video, which is (truely) 'captured'.
 
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Citizen_Kang
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Re: DV capture
Reply #2 - Sep 21st, 2001 at 9:01pm
 
Hey Rad,

That sheds light upon a few things (and helps to reinforce Mark Twain's wisdom that "It ain't what you don't know that gets you in trouble; it's what you know for sure that ain't so").

I would never have thought that the 1394 handles device control too.  I would have expected a RF remote, with the 1394 just handling the transfer of  - key words - already "captured" DV.  But when I give some thought to it, I can see that that would definetly not be an ideal situation for editing.  Do high end DV equipment employ a seperate transfer and control bus? [it is apparent that you guys use good DV equipment, but my lack of experience and research in this field limits my ability to appreciate how far up the evolutionary spectrum they lie, and more precisely, how much further up the ladder one could climb (without placing two mortgages upon one's house to finance such purchases)].

I also noted my error in regards to USBv1, which uses a theoretical max of 12Mbps (or 1.5MBps), which self-explanatorily (I think I'm making up words now) explains why USBv1 is not suffucient to handle the - key words - transfer rate of DV.  When I wrote that last night I just confused (momentary lapse of reason caused by fatigue) the b with a B....which is pretty easy to do considering all the techno-babble specs I got dancing in my head (along with sugar plums, lucky charms and everything else...) 

I did not perceive that there was a difference between analog "capture" and DV's.  But clearly there is some sort of bandwidth/capturing capability issue that I am ignorant about.  Perhaps it lies in the nature of the "capturing", I don't know, but it is definitely an area that I will need to get around to reserching/understanding.  [For me, once I comprehend how the specs/numbers for a technology are derived, I  usually have a good understanding of that technology and its limitations.  It is with math & physics that I wade through most corporate marketing babble]. 

 
 
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Re: DV capture
Reply #3 - Sep 22nd, 2001 at 5:51pm
 
Yes, the more expensive (professional) systems, like Matox DigiSuite ($3k-7K) offer separate device control.

Typically better drivers = better (more responsive/precise) device control. Pinnacle excels at this.

Consider transferring the music from a (vinyl) LP to your hard drive. Vinyl = analog. It has to be converted to digital format first, before it can go on your HD. Whereas a CD is already in digital format. When you rip a CD, you're basically just transferring bits to your hard drive. Same concepts apply to video. DV = the CD of video.
 
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