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Re: Is a capture and playback device a passthrough or a pitstop?

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Jeff Greenberg
Re: Is a capture and playback device a passthrough or a pitstop?
on Dec 30, 2011 at 3:43:13 am

Frank,

I used a simple 'averaging' formula with the four dots, it's a valid method, but very destructive.

DCT (Discrete Cosine Transform) compression (used in MPEG, JPEG and DV formats) uses a mathematical formula to remove information without you visually knowing it's gone; it's lossy (once gone, in this case, it can never come back.)

The problem with this new data, is that any further operations (such as color correction) will expose how much lossage there is.

[Frank Black] "hat do you mean by this:

3) If hardware can't keep up - say BM is requesting to playback uncompressed video @ 1080 and the drives aren't delivering data fast enough, your system 'drops' frames.

Which drives are you talking about? In the camera? And what happens when the frames drop? How do they drop? How is the drop represented -- in layman's terms and in precise terms"


A camera that can't record the information is useless! So it's not a problem in the camera.

It's in the capture to the drives or the playback from the drives.

Let's say you're playing footage that is stored on the drives uncompressed. Arbitrarily, let's say the demand for uncompressed is 30 units per frame, or 900 units per second (30 frames x 1 frame of 30 units=900)

What if the drives can't push 900 units per second...but only 300. We'll get 1/3 of the information (remember, we're using chunks that we've called frames, and each is 30 units) So let's display every third frame and just skip the ones that we can't get in time.

Other factors: The drives may deliver 900 units, but we chose firewire which only delivers 400? Again, not enough data shows up and some data is ignored; since we're slicing them into 30 unit frames, we'll skip some to display an actual picture.

Factors that can 'fail' - drives, drive attachments (esata, firewire, USB), computer failure (CPU capability, Graphic card capability or Ram capability.)

-----

Oh, you asked for specific too? Go back and change units to megabits per second and then it's specific. (P.S. Yeah, I did some fudging, but it's forgivable.)


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