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Noobie question. What could cause a ripple in the video?

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Eric RuffNoobie question. What could cause a ripple in the video?
by on Nov 11, 2009 at 3:51:26 am

I am just getting my setup together. Got an HPX 170 today and did a little test shot, interior of our house at night. Using my wife's old G4, successfully got the P2 footage onto and internal 200 2T 7200 rpm drive on the new Mac Pro which has the AJA KONA LHi card installed. Opened a new M100 Suite program and imported the P2 footage (oddly, I thought I shot in 720p/60 but Media 100 insisted the timeline be a 720p/59.nn timeline rather than a 720p/60 timeline...hmmm).

Here's the rub. Reviewing the footage in the M100 source (screen) monitor shows an occasional (2 or 3 times over a 10-15 second clip) horizontal "ripple" moving up the video playback. I don't believe the ripple is in the footage itself, and it manifests itself not always at the same exact point in the clip. I tried to use Snapz Pro to screen capture the problem so I could show it to someone, but the .mov file from Snapz Pro doesn't show the problem. It's like you can't photograph a ghost or something.

The ripple itself is sort of a horizontal shift, where the upper part of the video is offset to the right (or left, I can't remember) a little from the lower part of the frame, but the horizontal demarcation line of the upper and lower part of the frame gradually moves up the frame (from the bottom) and eventually the ripple disappears off the top so everything is fine again. I say gradually, but the ripple really only takes a second or two, bottom to top. It seems to take place during pans rather than when the camera is still or zooming.

I am wondering if my graphics chip is too weak for the job. It's a GeForce NVIDIA GT 120 which is the standard, bottom-of-the line card that was recommended to me for use with M100. The Mac Pro has a ton of ram from OWC and is a new quad core Nehalem running at 2.9GZ. The display is a 30" Apple.

I am hoping one of you guys will snap your fingers and tell me exactly what is going on. I am a little concerned that my description of the ripple is not very clear and you folks will have no idea what I am talking about.

Here's one more hint. If I stop the playback using the Edit window controls, so that I can freeze the playback and stare at a ripple in progress... it's gone. That is, I cannot get a still shot of the ripple; stopping the playback makes it go away.

Hmm.

-Eric


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Floh PetersRe: Noobie question. What could cause a ripple in the video?
by on Nov 11, 2009 at 8:02:38 am

[Eric Ruff] " (oddly, I thought I shot in 720p/60 but Media 100 insisted the timeline be a 720p/59.nn timeline rather than a 720p/60 timeline...hmmm). "
Maybe you don´t know it, but you wanted to shoot 720p59,94, and you did ;-)
"720p60" is in most cases 720p59,94; as far as I understand this is somehow related to this NTSC drop frame thing. Luckily we in Europe do not have to care about this.

Regarding your ripple: this sounds like you are monitoring your video on a computer screen? If yes, then this is most likely the reason for this ripple. Most LCDs work at a fixed refresh rate. Now if your screen e.g. works at a refresh rate of 65Hz, and your video runs at 60fps or 60 Hz, you will get into a situation where the display refreshes "between" video images. Like, the top of the viewer window already displays the "new" frame, where the bottom displays the old frame. Since you stepped through your clips and the problem is not present there, this has to be related to the display refresh.
Since you cannot change the refresh rate of a TFT, you either have to live with the problem during playback, or you need an external video display to monitor your footage.There you most likely don´t see that problem.




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Wickham StrubRe: Noobie question. What could cause a ripple in the video?
by on Nov 11, 2009 at 4:29:03 pm

I think Floh's right on with the ripple problem.

I can offer a bit more on the "what frame rate am I really shooting?" question.

With P2 especially, it pays to follow the media all the way down the chain to see how the camera menu relates to the frame rate of the media created and how both those details relate to the name that QuickTime uses for the codec.

I've got a Panasonic AG-HVX200P here on my desk. When I go through the process here's what I find.

- The camera menu calls it "720P/60P"

- The CLIP xml for the shot on the P2 volume lists the codec as "DV100_720/59.94p" and the framerate as "59.94p".

- After importing, Media 100 shows the codec as "DVCPRO HD 720p60" (the same name that QuickTime Pro uses. Try exporting from QTPro to see the codec names).



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Eric RuffRe: Noobie question. What could cause a ripple in the video?
by on Nov 12, 2009 at 3:22:55 am

Wickham,

Does that mean that these Panasonics always shoot at 59.94 even though you think specify 60? If so, why does Media 100 even offer a 60 time line; why not just offer 59.94?

-Eric


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Wickham StrubRe: Noobie question. What could cause a ripple in the video?
by on Nov 12, 2009 at 4:56:01 am

We try to offer any format that the hardware supports.



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Eric RuffRe: Noobie question. What could cause a ripple in the video?
by on Nov 12, 2009 at 3:15:10 am

Floh,

You were correct. I hooked up an external monitor and the ripple does not appear.

Thanks for your help; I would never have figured this out.

-Eric


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