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MPeg2 GOP problem


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#1 Invivo

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Posted 02 April 2006 - 01:32 AM

Just got a new Sony HVR-A1U tried it for the first time on a project that was critical, (first mistake) for footage that cannot be reshot. Now I am trying to work on it from home (Spring Break) using my home PC, (wish I had the school lab right now!). Using Premire 2.0 to capture HDV.

Footage was recorded in i1080 NTSC and MPEG2 GOP. Connected with FIREWIRE to Premire 2.0. Viewing on CRT with 1280 x 1024 resolution. Computer is AMD 64 3000 with 1GB memory. Comparable to a Pentium 4 at 3.0 GHz.

Resulting video file has horrible motion artifact. I have checked all settings from Camera to software. Hardware, Codecs, and firmware. I cannot find the problem. To describe the type of artifact picture is fine when there is no motion, but when a person would walk into frame their body outline becomes sawtoothed and is distorted as if the lines of resolution is offset from the first. Similar to the body looking like it is built out of Lego's.

Please if anyone is familiar with this could you reply and save me so I might make my deadline?

Thanks for any help you can give.

tt
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#2 Phil Rhodes

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Posted 02 April 2006 - 06:45 AM

Hi,

I think you are probably just seeing interlacing (look it up). This will appear on a computer monitor but, assuming you have everything set up right, an interlaced display such as an HD monitor or TV should display it correctly.

Post a still.

Phil
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#3 Invivo

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Posted 02 April 2006 - 04:59 PM

Thanks for the reply.

Frame by frame everything looks good on my computer. When posted on web it looks like this. Posted still at...

https://home.comcast...mages/still.bmp



Also here is a few seconds of the captured footage using Nero (same effect)....

https://home.comcast.../NVECapture.mpg



I did wonder if Interlacing was my problem, but all HD is "top first", right? And other footage shot by professionals appear normal on this same computer. Am I way off here? Or is it there Post Processing that makes the difference?
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#4 Invivo

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Posted 03 April 2006 - 07:39 PM

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#5 Phil Rhodes

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Posted 03 April 2006 - 09:32 PM

Hi,

Yeah, it's interlacing. If you want it to look good on a computer, you'll have to deinterlace it, otherwise, ignore the artifact until you get around to playing it back on an HDTV, whereupon all should appear normal. "Footage shot by professionals" has at least some chance of having been shot progressively, which obviates all these concerns.

Notice that if you rescale that image in your web browser it looks even worse, because of the rough scaling applied by the browser - depending how your edit app downsamples the video for display in a small window, it can do all kinds of odd things.

Go and google for general background info on interlaced video so you better understand what you're seeing, and I'm sure it'll all make sense.

By the way, did you notice there's actually a dropout in that frame, across the shirt of the right-hand guy at about tie-knot level? That's a different issue.

Phil
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