Blocky interlace problems from capture

Skratch wrote on 7/1/2010, 3:54 PM
I've captured some miniDV's vis firewire using Vegas 8c.When I play back the captured AVI... with camera pans, or motion within the frame, I'm getting a horizontal mismatch accross the frame. I can see interlace lines in the the Vegas preview window, but not in the camera viewfinder. There don't seem to be any setting adjustments in the camera preview options. I need some ideas on what settings to use and rid this artifact.

Comments

rmack350 wrote on 7/1/2010, 4:56 PM
If this is *just* interlace lines then it's nothing new. Your computer screen is progressive, not interlaced. However, if it's "blocky" then that's a bit weird.

The test is to play this interlaced DV back out to an interlaced screen and see how it looks. Usually you can do this by passing the signal from Vegas back out over firewire, through your camera and then to a TV or SD monitor. Search Vegas' help file for something like External Preview.

Rob
John_Cline wrote on 7/1/2010, 5:04 PM
Set it to "Preview - Auto" and just for good measure, under the project settings, set the deinterlace method to "Interpolate."
Marc S wrote on 7/1/2010, 7:34 PM
I've been noticing some really wierd interlace artifacts on some Mini DV as well and I'm wondering if it has something to do with Windows 7. I don't edit much with mini DV anymore but I never saw this while using Win. XP and Vegas. Are you using Win 7?
Skratch wrote on 7/1/2010, 7:41 PM
I'm actually using Vista Ultamate. It's a thin horizontal bar of frame (just above the midline of the whole frame) that doesn't keep up with the rest of the pan, or rapid movement in the frame.
rmack350 wrote on 7/1/2010, 10:30 PM
Just one bar? not a comb-like artifact on everything moving?

Rob
Skratch wrote on 7/1/2010, 10:36 PM
Just one bar. I did a couple of recaptures with properties set on interpolate, and preview good. Enlarged my capture screen and all looks good during the capture, Still getting the artifact in some spots Starting to wonder if it's windows media player, or even the heads on the cassette player? This is a new PC desktop i plan to use for capture. We'll see how they play on my laptop.
rmack350 wrote on 7/1/2010, 10:47 PM
If you get a chance to post a frame here that might be helpful. There's a sticky at the top of this forum that explains how to do it (you could post the image on Picassa or Flickr and then link to it)

Rob
willqen wrote on 7/1/2010, 10:49 PM
Don't think it's your computer. Sounds like a hardware problem. Are you using a deck to transfer your files to the computer, or using your camera to play the tapes ? Maybe your playback head in the camera may be dirty, or some such problem.
Skratch wrote on 7/2/2010, 12:20 AM
Using the DV camera deck... however, I just transfered the files to my laptop and they play without the artifact. That leaves something wrong with Windows media player, or my video card in the desktop? Radeon HD 4870. doesn't make sense.
farss wrote on 7/2/2010, 3:08 AM
Sounds like its a common artifact caused by the difference between the video's frame rate and the video card's refresh rate.

Bob.
Skratch wrote on 7/2/2010, 11:15 AM
Hm, didn't happen with my old PC. Same moniter, but generic video card.
rmack350 wrote on 7/2/2010, 8:47 PM
Hmm... Would the position of the artifact change if you moved the preview window around the screen?

Yeah, different PCs could drive the same monitor at different frequencies. This is usually configurable in the graphics card's control panel.

I'm kind of not buying this, but if this were the answer then it wouldn't show in a frame grab.

rob
farss wrote on 7/2/2010, 11:16 PM
"I'm kind of not buying this, but if this were the answer then it wouldn't show in a frame grab"

Me either but in the lack of anything concrete to look at one theory is as good as the next. So far it would seem it's not on the tape and it's not the fault of the capture and it only happens during pans.
My immediate reaction when I see something nasty during preview is to step through the offending section frame by frame. Very easy to waste a lot of time chasing ghosts.

Bob.
rmack350 wrote on 7/2/2010, 11:48 PM
Very easy to waste a lot of time chasing ghosts.

:-)

Yep. It's easy to put a lot of effort chasing down something that's not a real problem, or not the real problem. Like troubleshooting someone's network problem. Sometimes things aren't really broken until you've tried to fix them.

If it's a video framerate competing with a screen frequency then the problem would disappear when you stop playback or when you export a still image. If this were happening then I'd imagine you'd see a kind of offset between some portion of the top and bottom part of the frame. A bisection rather than a bar, and I'd think it'd appear higher or lower as you play the video. Not in the same spot in the frame.

This could very well just be an annoyance. If the output to an SD monitor looked okay then that's what I'd rely on.

Skratch wrote on 7/3/2010, 10:28 AM
Yes, you could call it a bisection? One strand of the frame is mismatched, or lagging during pans or motion moving accross the frame. It only occurs on playback of a captured AVI, so I can't catch a freeze, or don't know how I would from Windows media player. The artifact doesn't show up in the Sony preview window during capture or when bringing the file into the timeline.