MAC OS X: Forum

Snowy video

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Brad WilliamsSnowy video
by on Apr 21, 2011 at 2:17:05 am

I have a major problem. Let me see if I can explain this. For one of our campus churches, they play a one week delayed message that is a QuickTime file codec is HDV 720P, of course 1280x720. It is played from an 2 month old IMac.Video out is the display to dvi adapter which hits a dvi to HDMI cable. This inputs into a Kramer 729 scaler/switcher. Output out of the scaler dvi-d to an Extron box which then is cat-5 to a digital production HD projector which then has another cat-5 to dvi. Here is the problem. On playback, the video file will sometimes play fine and then like tonight it will flash to a white or gray screen for a second and then be ok. The audio never changes. Tonight it went to snowy screen z6 times and yesterday played with no issues. Any ideas what this could be ? We are pulling our hair out.


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Jeff GreenbergRe: Snowy video
by on Apr 21, 2011 at 3:48:11 am

No idea what the problem is. And if it's fine on the mac - it's somewhere AFTER the mac that the problem exists.

But I can tell you how to troubleshoot:

Find a way to monitor the output after each step along the chain. Barring that, you'll need a way to replace each unit/cable to see if it's the problem.

Best,

Jeff G

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Mark SuszkoRe: Snowy video
by on Apr 21, 2011 at 9:02:50 pm

First, that signal chain sounsd overly complicated.

Second, have you cleaned out the computer really well, purged old unneeded files from the scratch drive, that sort of thing? Could be you've got enough fragmentation built up in the hard drive that it is getting in the way of clean playback. AMcs are supposed to defrag themselves continuously inthe background. Still, when video starts getting messed up, I begin to suspect video RAM overheating or going bad, or virtual RAM space or the disk itself having read issues.


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Craig Thomas QuinlanRe: Snowy video
by on Apr 22, 2011 at 6:31:39 pm

Sounds like it may be an HDCP handshake issue. Take a look at this doc explaining the issues with hdmi/dvi hdcp handshaking.

http://www.quantumdata.com/resources/White%20Paper/HDCP_WP.pdf

Is everything in the chain here HDCP compliant? Intermittent blinking or snowy video is characteristic of a handshake issue.


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