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Jeff Greenberg
Re: Is a capture and playback device a passthrough or a pitstop?
on Dec 27, 2011 at 1:51:39 pm

Frank or Val,

Sure, I'll take a crack at this!

1) I think the answer has nothing to do with hardware or pipelines for the most part.
There are two types of compression: Lossless and Lossy.

Lossless compression your familiar with - you've zipped a spreadsheet, right? When you send it to someone else, it's crucial that it arrives with all the data - otherwise we're in real trouble with our financial data!

Lossy compression is like the JPEG we have on our still cameras. It's possible to average some of the information and throw out some of the data that your ey just can't see. For example, at a distance, somebody is holding up a square of 4 lights–3 of them bright green one of them a darker green. We could, average all that to be just one group of 4 dots all just a little darker than the bright green. Less information, but your eye and brain can't really tell the difference. We've lost information, but we have a picture that your eye and brain pretty much interpret as what happened.

Where I think you're getting confused is this–most professional compression schemes used by editorial software are lossy in nature. To display an actual picture though, the last step decompresses this lossy nature back to the full picture (uncompressed).

2) In a DV world (for example), Data on your HD (compressed), goes down the FireWire cable (Compressed), hits the cameras chip during playback for display and the chip uncompresses the lossy information back to full raster.

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.

4) I don't understand this question.

Best,

Jeff G


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