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Playing a Video with a Alpha Channel

Hi, just a quick post to see if this is possible.

I'm trying to play a video with a alpha channel (much like a decal but moving) and I've had no such luck. I've tried multiple formats (avi, mov, mp4 etc) with no real result. I always end up with the video playing with a background, where as I need it to have no background and just the coloured objects in the video. The flipbook technique is the closest I've come to it but theres no control over FPS and with the style I assume it wont hold a video file for longer than a few seconds. Any help of advice would be great, thanks!

Product Version: UE 4.17
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asked Oct 11 '17 at 01:24 PM in Using UE4

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domridley_affari
23 4 8 11

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2 answers: sort voted first

We've had success with an Over/Under Alpha approach for video where the top half of the video acts as the alpha mask and the bottom provides the RGB values. Then it's just a matter of some UV material math. This way your mask and RGB values are always in sync.

This has also been more desirable for mobile development since playing more than one video at a time can be taxing.

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answered Oct 16 '17 at 01:38 PM

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HidingGlass
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avatar image gmpreussner STAFF Oct 23 '17 at 02:12 PM

This is a good approach, thanks!

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Most video containers do not support alpha channels. There are only a few formats that do, and those are currently not supported by any of our player plug-ins. The only player plug-ins currently available with alpha support are ImgMedia for EXR/BMP/PNG image sequences, and NdiMedia (https://github.com/ue4plugins/NdiMedia) for real-time video over IP. This is in 4.18.

You may be able to use two separate videos, one that contains the fill (RGB) and one that contains the alpha channel. You can then blend the two together in a material. Please note that synchronizing two players is still somewhat limited, and your results may vary. It will help to use the exact same encoder settings on both videos.

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answered Oct 16 '17 at 12:44 PM

avatar image Artsell Sep 14 '18 at 09:14 PM

We just released a media player plug-in that support alpha channel:

https://www.unrealengine.com/marketplace/blvd-media

Enjoy!

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