External textures cannot be directly assigned as a brush texture; you need to assign a material that samples from an external texture instead since it generates special shader code to access it.

Steps to Reproduce
  1. Create UI Widget
  2. Create Movie Player / media texture
  3. Open UI Widget and assign media texture to a widget

This should not work; you need to create a slate material that uses a media texture and assign the material instead.

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ComponentUE - Editor - UI Systems - Slate
Affects Versions4.20
Target Fix4.21
Fix Commit4356067
Main Commit4676940
Release Commit4432953
CreatedSep 7, 2018
ResolvedSep 11, 2018
UpdatedJan 4, 2019
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