overlay of hdmi sources - AVS Forum
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post #1 of 4 Old 01-23-2011, 04:57 PM - Thread Starter
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I've been searching how to overlay one hdmi source (ppt text) on top of another hdmi source (video) but haven't found such a device. I've also looked at Kramer, Gefen, and Atlona websites.

I'd like to work with up to 8 hdmi inputs, overlay 2 of them, and then provide an hdmi signal out (either the overlayed combination of 2 sources or one of the other 6 hdmi sources).

Anybody know if there is a device that will overlay and switch hdmi sources to one hdmi output?

Thanks,

Jeff
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post #2 of 4 Old 01-23-2011, 11:16 PM
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Overlaying a video image on top of another, which in the production world is called "keying", is actually rather complex. The three main techniques are chromakey, which determines which image wins based on color (thus green-screen techniques, etc.), lumakey, which determines the winner based on pixel brightness, and alphakey or linear keying which has a separate signal giving the opacity of each pixel in the key.

There are quite a few keyers out there, but they are all aimed at the production market and are thus very expensive (e.g. multiple thousands of $$) and for HD signals they all pretty much use HD-SDI and not HDMI. I found a few video mixers that take DVI inputs, but the most I could find was 2 DVI in on a mixer that was a few thousand $.

If you're doing stuff in standard def and want to switch to composite or S-Video, then you can do it cheap. You might be able to make it work with component, but I didn't see any HD-ready analog video mixers. If you want to stick to HDMI, you're out of luck. Even if you wanted to try going the HD-SDI route, HD-SDI does not do HDCP, so most likely you'd still be stuck.

Lyle Corbin
www.crystalclearhometheater.com
THX Video, ISF, and HAA Level II calibrator
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post #3 of 4 Old 01-24-2011, 06:44 AM - Thread Starter
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Quote:
Originally Posted by XrstalLens View Post

Overlaying a video image on top of another, which in the production world is called "keying", is actually rather complex. The three main techniques are chromakey, which determines which image wins based on color (thus green-screen techniques, etc.), lumakey, which determines the winner based on pixel brightness, and alphakey or linear keying which has a separate signal giving the opacity of each pixel in the key.

There are quite a few keyers out there, but they are all aimed at the production market and are thus very expensive (e.g. multiple thousands of $$) and for HD signals they all pretty much use HD-SDI and not HDMI. I found a few video mixers that take DVI inputs, but the most I could find was 2 DVI in on a mixer that was a few thousand $.

If you're doing stuff in standard def and want to switch to composite or S-Video, then you can do it cheap. You might be able to make it work with component, but I didn't see any HD-ready analog video mixers. If you want to stick to HDMI, you're out of luck. Even if you wanted to try going the HD-SDI route, HD-SDI does not do HDCP, so most likely you'd still be stuck.

Thanks. I was hoping to overlay ppt text from a pc over a video source for church service. We've extended hdmi (dvi only right now from the pcs) about 100 ft. with the Kramer coax-to-hdmi devices and we're trying to eliminate our s-video sources.

Based on your input, which supports what I've discovered, I'll march on with a basic 8x1 hdmi switch, either from Kramer, Gefen, or Atlona.

Thanks again,

Jeff
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post #4 of 4 Old 01-24-2011, 08:30 AM
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For church services you have more options because you can use your computer as the keyer. For example, SongShow Plus allows you to use a DV video feed as the background of its presentations, and they support some special hardware to mix video feeds as well (http://www.songshowplus.com/Features...4/Default.aspx). - I think you want Example 3 on that page. MediaShout and others may also support features like this. Look around and see what you can find.

Lyle Corbin
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THX Video, ISF, and HAA Level II calibrator
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