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Alpha Channel Output


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Did anybody sent an output from Display PC with Alpha Channel ? Is that possible ? If possible is there any settings needs to be done at Watchout or the settings need to be done on the graphics card ?


What I try to achieve is to send a video with a circle with alpha channel in the center to my Analog Way Ascender and use it as top layer. And place the camera layer under that so the output of Watchout will be masking the live feed.


Thanks in advance.


Sedat Gündüz

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Uhmmm, this has nothing to do with alpha channel though, does it? A signal on dvi or whatever can't contain an alpha channel as it will just output black (or white). In your ascender (or encore, spII, spyder) you will have to adjust the signal to be used as a key signal for the camera to show. No sense in using an Animation codec, a simple h264 will do of course. Used this soooo many times.

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You could fill the circle with say pure green or similar, and key that out in the Ascender.

 I don't know how the Ascender interprets aplha channels. It may just ignore them. In which case the above method would be a workaround. Experimentation will dictate the most suitable colour for keying. Obviously if it was a football match then green would not be the best choice...

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You might consider treating this the same way an external keyer is implemented.

i.e. you send two channels / outputs, one with the video information and a second with the keying information.

The key signal is then used by the device receiving the signals to mask the video content signal.

This provides complete control of the keying and avoids any issues with colors in the video signal.

I do not know anything about the Analog Way Ascender's capabilities,

but external keyers are commonly used in news or weather broadcasts,

this is a commonly supported method in the broadcast industry.

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AnalogWay Ascender (and also NexTage and brothers) do NOT have any external keying function.

I think this is the only deficiency of this equipment that I consider the top of the class in any other aspect.

Asked AnalogWay to work on it.


The Barco Encore and ScreenPro II names the external keying feature as "cut & fill".

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  • 7 months later...
  • 2 weeks later...

Hello everyone, two days ago we did a show with 4 videos running at the same time with RGB + alpha channel. These videos were on a top layer of another 3 videos. We used the hap codec to do this. You need to install the codec both in the display and production computers.



-1 production computer

-1 mac pro (cylinder) with bootcamp with 2 VGA (2 projectors) and 1 HDMI (LED screen) outputs. All 1600x1200px.




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You need to install the codec both in the display and production computers.



Presumably you're talking about WATCHOUT 5, since WATCHOUT 6 includes an optimized HAP playback codec, and doesn't need the QuickTime version (which really isn't designed to act as a high-performance playback codec).
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